THE UNIVERSITY OF ILLINOIS LIBRARY G307 CHECK FOR UNBOUND CIRCULATING COPY Response of Illinois Soils to Limestone BY F. C. BAUER UNIVERSITY OF ILLINOIS AGRICULTURAL EXPERIMENT STATION BULLETIN 405 (June, 1934) CONTENTS INTRODUCTION 303 Forty Fields Furnish Data for Study 303 Widely Varying Soil Conditions Represented 305 Amounts and Kinds of Lime Materials Applied 305 Crop Rotations Followed 307 DIFFERENCES AMONG SOILS IN RESPONSE TO LIMESTONE. ... 307 Response as Related to Natural Productivity 307 Response as Related to Chemical Factors 310 Data From Fields Discontinued Before 1931 314 RESPONSE OF INDIVIDUAL CROPS TO LIMESTONE 316 Corn 316 Wheat 320 Oats 323 Hay Crops 324 Comparative Responses of Above Crops 326 Responses of Legume Crops 327 EFFECT OF LIMESTONE ON SOIL PRODUCTIVITY LEVELS 331 RAPIDITY AND TREND OF RESPONSE TO LIMESTONE 334 Dark Soils With Heavy, Noncalcareous Subsoils 335 Dark Soils With Open, Noncalcareous Subsoils 335 Dark Soils With Impervious, Noncalcareous Subsoils 335-337 Yellow Soils With Noncalcareous Subsoils 338 Gray Soils With Impervious, Noncalcareous Subsoils 339-341 Other Soils Represented by Single Fields 341 General Discussion of Response Trends 341 Lasting Effects of Single Applications of Limestone 343 Response Trends as Related to Total Yields 344 ECONOMIC RESPONSES TO LIMESTONE 346 Acre- Values of Crop Increases 346 Ton- Values of Limestone as Measured by Value of Crop Increases.... 349 Problems of Economic Worth 351 RELATION OF LIMESTONE TO VARIOUS SOIL PRODUCTIVITY FACTORS 352 Soil Acidity 353 Phosphorus Availability 354 Potash Availability 357 INCREASING USE OF AGRICULTURAL LIMESTONE 359 SUMMARY AND CONCLUSIONS.. . 360 Urbana, Illinois June, 1934 Publications in the Bulletin series report the results of investigations made by or sponsored by the Experiment Station. Response of Illinois Soils to Limestone By F. C. BAUER, Chief, Soil Experiment Fields ,OILS derived from limestone are usually productive and dur- able. This fact is widely recognized in such time-honored phrases as "a limestone country is a rich country." Not all soils, however, are derived from limestone and hence they may be naturally lime-deficient. Then, too, soils in humid climates tend to lose the lime materials naturally contained in them more or less rapidly thru the drainage waters and hence may become lime-deficient thru the operation of natural forces. With increasing deficiency of lime, soil productivity becomes lower and crop yields are reduced. The pre- vention and correction of lime deficiencies has become an important problem in soil management. The effect on soil productivity of treatments to prevent and cor- rect lime deficiencies has been studied for many years by the Illinois Agricultural Experiment Station. Field experiments have been con- ducted under widely varying soil conditions. The facts revealed have been widely disseminated thru publications and otherwise and profit- ably utilized by many farmers in Illinois and elsewhere, but because of the interest in and importance of such studies it seems desirable to bring all the facts together in summarized form. In this publica- tion data have been assembled showing how various kinds of soil re- spond to applications of lime materials. Analysis of the relative ef- fectiveness of different methods of applying limestone, including rates and frequency of liming, and of different finenesses of limestone and different forms, is reserved for future publications. Forty Fields Furnish Data for Study The first field experiments dealing with the influence of lime materials on Illinois soils were established in the fall of 1901. During the next seventeen years more than forty such fields were established over the state, and lime in some form, usually limestone, was given a prominent place in the treatment scheme. In these experiments lime materials proved of different value on different soils. On many soils they were indispensable for successful crop production. On some soils they proved highly desirable for ef- ficient production. On other soils they were without any physical effect, or the effect was so minor as to have no economic value. As the facts about these experiments became known among Illinois 303 304 BULLETIN No. 405 [June, farmers, widespread interest developed in the use of limestone for soil improvement, in which Illinois took the lead. Many of the Illinois soil experiment fields are still in operation. With the passage of time they not only continue to demonstrate the O FIELDS DISCONTINUED BEFORE 1931 JOLIET9 SPRINGVALLEY ALEDO KEWANEE OOUAWKA / MINONK FIELDS IN OPERATION THRU 1931 FIG. 1. LOCATION OF SOIL EXPERIMENT FIELDS FURNISHING DATA FOR THIS PUBLICATION Twenty-five of the soil experiment fields whose responses to limestone are analyzed in this publication had been in operation for periods varying from fourteen to thirty years up to and including the 1931 crop season. Fifteen other fields, operated for varying periods, were discontinued before 1931. value of lime materials for soil-improvement purposes, but they also are bringing to light new management problems. The more recent results indicate, in addition to the facts stated above: (1) that non- responsive soils may, with continued cultivation, become responsive; and (2) that the chemical, physical, and biological changes produced by the application of lime materials to the soil may in time create new conditions that must be taken into account in planning management practices. Forty of the fields established between 1901 and 1918 supply the 1934] RESPONSE OF ILLINOIS SOILS TO LIMESTONE 305 data for the present study. Twenty-five of these fields were still in operation in 1931, thus furnishing data for periods of fourteen to thirty years. Four of these fields were discontinued at the end of the 1931 season. Widely Varying Soil Conditions Represented A wide diversity of soil conditions and soil types is represented by the Illinois soil experiment fields, tho the types can be classified into ten general groups. The general characteristics of those soils, together with some information about their natural productiveness, certain of their chemical qualities, and the limestone applications made to them are outlined in Tables 1 and 3. The groups are arranged in descending order according to their natural productivity, a sequence which is maintained thruout this publication. During the early years of these experiments no attempt was made to obtain detailed information about the character of the soils on which the fields were located. Only the general nature of the fields that were discontinued is therefore known. Amounts and Kinds of Lime Materials Applied No uniform plan for the application of lime materials was in effect during the early years of these experiments. Slaked lime was the chief material used in the earliest experiments. It was applied at rates ranging from 285 pounds to 10,000 pounds an acre. The usual appli- cation was 400 to 500 pounds an acre and was made at irregular in- tervals. Ground limestone in amounts ranging from 600 pounds to 20,000 pounds an acre was sometimes used. On some fields regular applications were made every year for several years. On other fields large amounts were applied, and usually no further applications were made for considerable time thereafter. In 1909 and 1910 a more uniform practice was adopted. Crushed limestone became the standard material. Initial applications were made at the rate of 4 tons an acre, the plan being to follow with ap- plications once during each rotation period at the annual acre-rate of 1,000 pounds, all to be made to the plowed soil just ahead of wheat seeding. This plan was followed on most fields until 1922 and 1923, when it became clear that on most plots more limestone was being applied than was necessary. All applications were then stopped, the plan being to apply no more limestone until the need for it should appear. In these experiments the lime materials were usually applied in addition either to farm manure or to crop residues in order to repre- 306 BULLETIN No. 405 [June, TABLE 1. SOIL GROUPS, NATURAL PRODUCTIVITY LEVELS, AND AMOUNTS OF LIME- STONE APPLIED TO ILLINOIS SOIL EXPERIMENT FIELDS IN OPERATION THRU 1931 (Soil groups and fields are listed in order of natural productivity) Soil groups and fields Stage of development Natural productivity as average acre-yields First crop year after limestone applica- tion Total amount limestone applied All crops Corn I. Dark soils with heavy, noncal- careous subsoils Hartsburg, Logan county .... LaMoille, Bureau county .... Aledo, Mercer county .... Young Young Young Young Ibs. 2 600 2 524 2 396 2 388 2 477 2 408 2 372 2 210 2 068 2 139 1 690 1 748 1 723 1 661 1 476 1 652 799 684 494 589 731 611 608 558 527 500 482 574 325 bu. 49.0 46.8 54.8 48.2 49.7 54.6 36.1 44.0 40.1 42.0 30.1 34.4 35.2 26.5 29.0 31.3 19.6 14.2 15.4 14.8 19.8 18.8 18.0 14.1 12.7 10.1 10.7 14.9 11.5 1912 1913 1912 1912 1915 1915 1913 1912 1914 1913 1913 1911 1910 1914 1911 1913 1912 1913 1902 1910 1916 1913 1910 1918 tons 8.50 7.75 8.25 8.25 6.75 6.75 7.75 8.25 7.40 7.75 7.75 8.75 9.25 7.90 8.75 7.75 8.25 7.25 8.95 9.25 6.75 5.50 9.25 5.25 Minonk, Woodford county. . . II. Dark soils with noncalcareous subsoils Young Semi mature Semi mature Semi mature III. Brownish-yellow soils with open, noncalcareous subsoils Springvalley, Bureau county. . IV. Dark soils with open, noncalcare- ous subsoils Mt. Morris, Ogle county V. Dark soils with impervious, cal- careous subsoils Young (erosion) Semi mature Semi mature Semimature Mature VI. Dark soils with impervious, non- calcareous subsoils Carthage, Hancock county. . . Clayton, Adams county Lebanon, St. Clair county.. . . Carlinville, Macoupin county VII. Sandy loams and sands Oquawka, Henderson county. . VIII. Yellow soils with noncalcareous subsoils Unionville, Massac county. . . Enfield, White county Semimature Mature Mature Average IX. Gray soils with impervious, non- calcareous subsoils Oblong, Crawford county .... Toledo, Cumberland county. . Odin, Marion county Old (moderately drained) Old (poorly drained) Old (poorly drained) Old (poorly drained) Old (very poorly drained) Old (poorly drained) Old (moderately drained) Sparta, Randolph county. . . . .Newton, Jasper county Ewing, Franklin county Average X. Hilly land Elizabethtown, Hardin county Mature sent both the livestock and the grain systems of farming. In the grain system a legume, usually sweet clover, has been seeded in a small- grain crop and plowed down as a green manure for the following corn crop. 1934\ RESPONSE OF ILLINOIS SOILS TO LIMESTONE 307 Crop Rotations Followed Definite crop rotations have been practiced on all fields. Usually each crop in the rotation has been grown each year. These rotations have varied somewhat, but on many fields wheat, corn, oats, and clover have been the standard rotation. In the grain system of farm- ing such a rotation is ideal for the use of sweet clover as a green manure for the corn crop. On a few fields a larger proportion of legumes was grown by adding alfalfa as a fifth crop in the rotation scheme. DIFFERENCES AMONG SOILS IN RESPONSE TO LIMESTONE The effectiveness of limestone in increasing crop yields on the different types of soil to be found in Illinois is indicated by the figures in Table 2 reporting the crop yields on twenty- four experiment fields in operation thru 1931. In order to have a common basis for compari- sons, the crops grown and harvested, excluding the stover and the straw, have been converted into pounds. Simple differences between the crop yields on limed and unlimed plots are one measure of the response of a soil to liming. Another useful measure is the ratio between such yields. Attention is called to such ratios in all the yield tables presented in this bulletin. Ratios of unity (1.000) or less indicate that the limestone applications failed to increase yields. Ratios greater than unity indicate that yields were increased and the extent of the increase in relation to yields from untreated plots. Thus a ratio of 1.365 represents a 36.5 percent in- crease in yield. Yields from limed plots, which are not always given, may be ascertained by multiplying the unlimed yield by its accompany- ing ratio. Response as Related to Natural Productivity It is evident from study of Table 2 that the response of soils to limestone tends to vary with their natural productivity and that the lower the natural productivity of a soil, the greater its response to limestone. The dark soils with heavy, noncalcareous subsoils, ranking first in natural productivity, gave practically no response, the increase in crop yields on the four fields in this group averaging only 3 per- cent in the grain system. The hilly land, ranking lowest in natural pro- ductivity, gave the most pronounced response, the crop yields on the one field in this group being increased more than 150 percent by lime- stone applications. The response of the other eight groups of soils ranged between these two extremes. 308 BULLETIN No. 405 TABLE 2. RESPONSE OF ILLINOIS SOILS TO LIMESTONE, AS INDICATED BY CROP YIELDS FROM EXPERIMENT FIELDS OPERATED THRU 1931 (Figures indicate average annual acre-yields of all crops grown, excluding stover and straws) Soil groups and fields in order of natural productivity Manure system Residues system Manure (1) Manure, lime- stone (2) In- crease (3) Ratio ML M (4) Resi- dues (5) Resi- dues, lime- stone (6) In- crease (7) Ratio RL R (8) I. Dark soils with heavy, non- calcareous subsoils Hartsburg Ibs. 3 102 3 175 3 095 2 914 3 071 3 020 2 782 2 956 2 886 2 921 2 144 2 489 2 491 2 386 1 922 2 322 1 386 973 736 854 1 090 890 Ibs. 3 418 3 198 3 401 2 904 3 230 3 158 2 904 3 273 3 101 3 187 2 499 2 858 2 953 2 666 2 616 2 773 2 334 1 437 1 660 1 548 870 682 Ibs. 316 23 306 - 10 159 138 122 317 215 266 355 369 462 280 694 451 948 464 924 694 780 792 1.097 1.007 1.099 .997 1.052 1.046 1.044 1.107 1.074 1.091 1.166 1.148 1.185 1.113 1.361 1.194 1.684 1.477 2.255 1.813 .716 .890 Ibs. 2 931 2 591 2 486 2 377 2 596 2 326 2 443 2 042 2 123 2 082 1 631 1 758 1 805 1 476 1 472 1 628 947 600 537 569 856 598 660 563 446 454 427 572 391 Ibs. 2 879 2 737 2 705 2 371 2 673 2 588 2 555 2 579 2 386 2 482 1 887 2 232 2 361 1 890 2 010 2 123 1 741 1 040 1 174 1 107 1 363 1 215 924 1 246 929 923 1 095 1 099 1 000 Ibs. - 52 146 219 - 6 77 262 112 537 263 400 256 474 556 414 538 495 794 440 637 538 507 617 264 683 483 469 668 527 609 .982 1.056 1.O88 .997 1.030 1.112 1.045 1.263 1.124 1.192 1.157 1.270 1.308 1.280 1.365 1.304 1.838 1.733 2.186 1.946 1.592 2.032 1.400 2.214 2.083 2.033 2.564 1.921 2.558 LaMoille Aledo Average II. Dark soils with noncalcare- ous subsoils III. Brownish-yellow soils -with open, noncalcareous subsoils IV. Dark soils with open, non- calcareous subsoils Mt. Morris V. Dark soils with impervious, calcareous subsoils Joliet VI. Dark soils with impervious, noncalcareous subsoils Carthage Lebanon VII. Sandy loams and sands VIII. Yellow soils with noncal- careous subsoils Unionville Enfield IX. Gray soils with impervious, noncalcareous subsoils Oblong Toledo Odin Raleigh 891 862 836 781 892 618 775 583 515 805 705 1 384 884 721 679 1 024 813 766 .992 .836 .812 2.311 1.911 2.239 Sparta Newton Ewing Average X. Hilly land Elizabethtown. . . The relation between the natural productivity of a soil and its response to limestone is not, however, entirely consistent, as may be seen from Fig. 2. Groups III and V, for example, show a somewhat 1934] RESPONSE OF ILLINOIS SOILS TO LIMESTONE 309 low response in relation to their natural productive levels, while Group VII shows an unusually high response. Each of these three groups of soils, however, is represented by only a single field, a fact that may partially explain the irregularities, especially since these fields repre- sent in some respects the extremes of their groups. The Joliet field, representing Group V, is exceptionally deficient in phosphorus ; the RELATIVE PRODUCTIVE LEVELS ACTUAL CROP INCREASES, POUNDS E3 PERCENTAGE CROP INCREASES 800 400 v 21 yn vnr SOIL GROUPS FIG. 2. COMPARATIVE RESPONSE OF TEN GROUPS OF ILLINOIS SOILS TO LIMESTONE APPLICATIONS The black bars represent pounds of crop increase produced by limestone, the shaded bars the percentage increases resulting from limestone. The natural productivity of the various soil groups compared with Group I is shown by the broken line. It is evident that the response of a soil to limestone varies more or less inversely with its natural productivity. Highly productive soils tend to respond the least and the less productive soils the most. Oquawka field, representing Group VII, is exceptionally sandy; and the Springvalley field, representing Group III, has a highly perme- able soil profile which permits deeper feeding of the crop plants. Quite different relationships between the actual yield increase on a given soil and the percentage yield increase (response ratio) are evident among the various soil groups. For all of the dark-colored groups the actual yield increases are more striking than the response ratios, while for the sandy and the light-colored groups the response ratios are more striking than the actual yield increases. Leaving the sandy group out of consideration and comparing the light-colored groups (VIII, IX, and X) with the least productive dark-colored group (VI), one observes that there is not a great deal of difference in the actual yield increases resulting from the use of limestone on 310 BULLETIN No. 405 [June, these soils. Evidently when natural productivity levels are very low, differences in level make little difference in the actual increases that can be obtained by applications of limestone. With actual increases in yield remaining the same, percentage responses will of course rise as the natural levels of productivity decline. Deficiencies other than limestone, along with other characteristics peculiar to these light- colored soils, such as stage of development, are undoubtedly impor- tant factors in the variations which they have shown in their response to limestone. Response as Related to Chemical Factors A study of limestone responses as related to the natural produc- tivity of the soil has increasing significance when one examines some of the chemical properties of the soil. Such chemical data are pre- sented in Table 3. These data include those obtained by the Comber potassium-thiocyanate test, widely used as a rapid field test ; those obtained from hydrogen-ion determinations, in terms of pH, 1 a meas- ure of active acidity or alkalinity; those obtained by the Bray-DeTurk lime-requirement test, 2 a field test based on the deficiency of exchange- able calcium; and some laboratory data pertaining to replaceable bases. 3 Replaceable-base data are now generally regarded as satisfactorily explaining the lime responses of soils. At this point it is of interest to consider in greater detail the data presented in Table 3. In Columns 2, 3, and 4 are shown the acre-amounts of replaceable calcium and magnesium in the different soil groups. In no group are the totals of these elements (Column 4) and the total base-exchange capacity of the soil (Column 5) equal on the unlimed land. The calcium and magnesium are insufficient to satisfy the total base-exchange capacity of the soil. This means that other replaceable bases are present, or 'A pH value of 7.0 represents neutrality. Decreasing values represent in- creasing acidity, and increasing values represent increasing alkalinity. Soils of good productivity are usually slightly acid, ranging in pH values from 6.0 to 7.0. A soil with a pH value as low as 4.0 is exceedingly unfavorable to the growth of ordinary crops. 'Method described in Soil Science 32, 5:329 (1931). 'When soils are mixed with salt solutions, a rapid exchange of bases takes place between the soil and the salt. The character and the quantity of the bases entering into this exchange depend upon the nature of the soil and the salt solution used. The calcium, magnesium, and other bases shown by such tests to be present in replaceable form are commonly referred to as "exchange- able bases." Chemists have found the results of such tests useful in explaining many behaviors of soils. Such tests are now widely used in soil-acidity and lime-response studies. 19341 RESPONSE OF ILLINOIS SOILS TO LIMESTONE 311 ( j iff! 1 I 00 -o - ,0 no tso o TfO ,0 ,0 o T 3 , Comber acidity KSCN s D u C C O O ZZ "Si X J Medium None E E .5 - .2 3* sg Sin SZ V II Medium None Very high None > c Si I 111 < n ob f! 3 . . 2 subsoils 3 2 c careous sub 1 : : | K ' k. J I : : <3 . . 3 . . oncalcareou and fields it " natural ctivity Q S - I M t 5 soi/5 with o soils a . . o . . c . . c V ' 0. o | : : * ' : * ill j j . : : I : : E 8 : : 2 ; : 2 "3 : : '. '. mpervious, n e c 111 MO 1 I. Dark soils with soils Hartsburg. . Hartsburg. . II. Dark soils with t Kewanee. . . . III. Brownish-yellow careous sub Springvalley. IV. Dark soils with soils Mt. Morris. . Mt. Morris. . V. Dark soils with subsoils Joliet Joliet VI. Dark soils with t subsoils Clayton. . . . Clayton VII. Sandy loams an Oquawka . . . Oquawka . . . VIII. Yellow soils wi Unionville. . Unionville. . IX. Gray soils with i subsoils Ewing Ewing X. Hilly land Elizabethtow Elizabethtow 312 BULLETIN No. 405 [June, else that hydrogen (indicating acidity) has taken their places. The pH values of the soil (Column 8) indicate that hydrogen is present. The amount of replaceable bases in the soil in proportion to the base-exchange capacity of the soil is indicated in Column 6 under the heading "degree of saturation." For unlimed land there is consider- able variation in the degree of saturation among the several soil groups. The Hartsburg field, representing the dark soils with heavy, noncalcareous subsoils, contains enough replaceable calcium and mag- nesium to satisfy 79 percent of the total capacity of the soil to absorb such bases. The Ewing field, however, representing the gray soils with impervious, noncalcareous subsoils, shows a saturation of only 17 percent. The other soils range between these extremes. Jt is now generally believed that when the soil contains sufficient calcium and magnesium in replaceable form to satisfy about 80 per- cent of the base-exchange capacity of the soil, limestone is not likely to be needed for crop production. When this value falls below 80 percent, indicating thereby decreasing availability of calcium and mag- nesium, limestone is needed for crop production. To say that a soil gives an acid reaction, or that it is an "acid soil," is another way of saying that it is deficient in available bases, especially in calcium and magnesium. So far as the growth of crops is concerned, calcium is the more important of these two bases. With these facts in mind it will be of interest to compare the de- gree of saturation of the different soils groups with their natural pro- ductivity levels and limestone responses. Such comparisons reveal striking differences between the dark-colored soils and the sandy and light-colored soils (Fig. 3). In the dark-colored groups of soils, which exhibit relatively high productive levels and rather low responses to limestone, the degree of saturation averages about 70 percent. In the light-colored groups, which are low in productivity and high in lime- stone response, the degree of saturation averages about 25 percent. Some of the individual soil groups within these two major classes of soils (dark colored and light colored) do not, however, conform perfectly to the above relationship. Group II, represented by the Ke- wanee field, for instance, falls to 55 percent saturation, yet natural productivity is high and limestone response is low. Referring to Column 5 of Table 3, one observes that the base-exchange capacity of this soil is high even tho the total replaceable calcium and mag- nesium is somewhat low in comparison. This soil also shows a fair degree of acidity. Apparently the use of the 80-percent saturation level as an indicator for the need of limestone on a soil of this kind 1934] RESPONSE OF ILLINOIS SOILS TO LIMESTONE 313 is too high. Soils with a high base-exchange capacity may be able to liberate more available calcium for crop growth than soils of low exchange capacities, even tho the total amount of replaceable calcium and magnesium is relatively low. On the Clayton field, representing Group VI, with 73 percent saturation, the productivity level is lower and the response to limestone higher than on the Kewanee field. The total base-exchange capacity of the soil of the Clayton field is, however, very much lower than that of the Kewanee field. For the Clayton field, therefore, the 80-percent saturation level may be a good index to the need for limestone. The same conditions prevail to some extent in the light-colored soils. 160 --RELATIVE PRODUCTIVE LEVELS PERCENTAGE BASE SATURATION ^PERCENTAGE CROP INCREASES -10 FIG. 3. DEGREE OF BASE SATURATION AND LIMESTONE RESPONSE IN TEN GROUPS OF ILLINOIS SOILS The base-exchange capacity of the highly productive soils tends to be more completely satisfied than does the base-exchange capacity of the soils of lower productivity, as shown by the percentage base saturation. Since the response that a soil will make to limestone applications is more or less closely related to its percentage base saturation, the value of proper chemical tests in detect- ing soils or fields that are deficient in limestone is evident. When the results of the various tests for lime requirement or acidity (Table 3) are compared with each other it is evident that there is not exact agreement among them. The Kewanee and Mt. Morris fields, for instance, possess about the same percentage satura- tion and pH values, but the amounts of acidity, as indicated by the Comber test, and the lime requirements, as indicated by the Bray- DeTurk tests, differ. This is to be expected since the tests are based on different principles and also because there are marked differences 314 BULLETIN No. 405 [June, in the chemical nature of the various kinds of soil. Because of the complexity of these various relationships, the problem of clarifying the underlying principles of soil acidity will probably always be beset with some difficulties. So far as the farmer is concerned, however, some of the simpler tests, such as the Comber field test for acidity, described in Illinois Circular 346, or the Bray-DeTurk lime-require- ment test, 1 will be of great service in quickly determining the approxi- mate lime needs of the soil or in detecting those fields or areas that will grow various legume crops without the application of lime materials. Data From Fields Discontinued Before 1931 The effects of lime treatments in the crop-residues system of farming on the soil experiment fields discontinued before 1931 are shown in Table 4. During the early years of the experiment fields no attempt was made to obtain detailed information about the character of the soil on which the fields were located. Only the general nature of the soil of most of the fields discontinued before 1931 is known. Neither was any TABLE 4. ILLINOIS SOIL EXPERIMENT FIELDS DISCONTINUED BEFORE 1931, SHOWING RESPONSE TO LIMESTONE IN RESIDUES SYSTEM OF FARMING Fields Duration of experiment (1) Natural produc- tivity, average corn yield (2) Lime applied Average annual acre-yields of all crops Kind (3) Total amount (4) Resi- dues (5) Resi- dues, lime (6) In- crease (7) Ratio RL R (8) Dark-colored soils 1902-23 1906-19 1905-10 1904-18 1906-09 1902-13 1913-27 1902-13 1902-29 1912-23 1913-22 bu. 57.8 49.5 45.7 58.3 43.7 47.5 43.6 34.2 54.6 29.8 26.5 44.7 30.9 11.2 18.2 17.9 47.0 f Slaked \Limestone Limestone Slaked Limestone Limestone Hyd rated Limestone /Slaked \ Limestone /Slaked I Limestone Limestone Limestone ton* .141 7.00J 6.90 .58 4.65 .70 .20 8.00 .581 3.06J .421 7.00/ 7.50 8.00 Ibs. 2 201 2 598 2 437 2 535 2 189 2 006 2 165 1 038 2 332 2 119 1 362 2 603 2 472 591 704 1 256 1 877 Ibs. 2 038 2 511 2 501 2 596 2 331 2 193 2 403 1 156 2 633 2 546 1 834 2 733 2 801 840 1 067 1 569 1 601 /6s. -163 - 87 64 61 142 187 238 118 301 427 472 130 329 249 363 313 -276 .926 .967 1.022 1.024 1.065 1.093 1.110 1.114 1.129 1.202 1.346 1.050 1.130 1 431 1.515 1.249 .853 Rockf ord Galesburg Myrtle Sibley Sidell Mascoutah Urbana Pana Light-colored soils 1903-11 1902-23 1902-17 Limestone Slaked /Slaked \Limestone 10.00 5.00 3.201 4.00J DuBois Cutler Sand soils Greenvalley .... 1902-07 Slaked .16 'Soil Science 32. 5:329 (1931). 1934] RESPONSE OF ILLINOIS SOILS TO LIMESTONE 315 uniform practice followed in the early use of lime materials. Never- theless the results from these fields are of interest, especially since they correspond fairly closely to the results obtained from the twenty- five fields still in operation in 1931. More or less variation in the natural productivity of the fields in- cluded in the group of dark-colored soils is indicated by the corn yields recorded in Column 2 of Table 4. This variation is due mainly to the fact that several different soil types are represented in this group. The interesting fact about the data from these fields, how- ever, is that the response to lime varies more or less inversely with the natural productivity of the soil. This is evident from a study of the figures in the last two columns. Those fields producing the highest average yields of corn without treatment have given little or no re- sponse to lime. As the natural productivity level declines, the re- sponse to lime tends to increase. On the Pana field, for example, which has the lowest average yield of corn, all crop yields have been increased more than a third by the use of limestone. Besides differences in response to limestone that result from dif- ferences in the natural productivity of the soil, we find differences in response because of the type of crop rotation employed. On a lime- deficient soil, rotations that include the liberal use of legume crops appear to make better use of applied limestone than do rotations that consist almost entirely of grain crops. The Urbana field, for example, on which alfalfa was grown regularly as one of the rotation crops, showed a very favorable response to limestone. On fields where the rotations consisted chiefly of grain crops, the response to limestone was somewhat unfavorable. The response of legumes to limestone is especially fortunate, for legumes improve the soil and may gen- erally be regarded as high-profit crops. The light-colored soils are not extensively represented by these fields. What evidence there is agrees with that of the fields reported in Table 2 in showing the productive levels of such soils to be much lower than those of the dark-colored soils and the degree of response to lime treatments to be considerably higher. On the one sandy field represented, the crops showed no response to the lime applied. 316 BULLETIN No. 405 [June. RESPONSE OF INDIVIDUAL CROPS TO LIMESTONE Corn The behavior of individual crops on various kinds of limed soils is also a matter of much interest. Increases in the yields of corn result- ing from the application of limestone are shown graphically in Fig. 4 and are also illustrated in Figs. 5 and 6. The natural productivity of the soil is clearly an important factor in the response of corn to applied limestone. The light-colored, less LIMESTONE AND MANURE W O -I DARK-COLORED SOILS LIGHT-COLORED SOILS LIMESTONE AND CROP RESIDUES FIG. 4. INFLUENCE OF LIMESTONE ON CORN YIELDS The dark-colored soils tend to give the largest increases in yields for lime- stone in the crop-residues system, while on the light-colored soils limestone gives the largest increases when used with manure. 1934] RESPONSE OF ILLINOIS SOILS TO LIMESTONE 317 productive soils have given significantly larger increases than the dark-colored, more productive soils. More or less variation in re- sponse on the different fields within the major soil groups is also evident. In the dark-colored group, for example, the naturally more productive soils tend to give the least response. In the light-colored Fie. 5. ON SOILS OF NATURALLY Low PRODUCTIVITY LIMESTONE Is USUALLY STRIKINGLY EFFECTIVE The acre-yield of corn on the unlimed land was 1 bushel, while more than 50 bushels were harvested from the limed land. Limestone is indispensable on many soils. Ewing field, 1928. group, the relationship between the natural productivity of a soil and the response made by corn to limestone applications is not so pro- nounced. On the dark-colored soils the residues system has caused larger increases in corn yields than the manure system. On the light-colored soils the manure system has given the larger crop increases. Ap- parently the manure takes care of the major soil deficiencies in the dark-colored soil, and hence there is less need for limestone. With the light-colored soils, however, deficiencies other than lime- 318 BULLETIN No. 405 TABLE 5. MANURE SYSTEM: RESPONSE OF WHEAT, CORN, OATS, AND HAY TO LIMESTONE ON ILLINOIS SOIL EXPERIMENT FIELDS (Yields are given as annual acre averages) Soil groups and fields in order of natural productivity Wheat yields' Corn yields 1 Oat yields 1 Hay yields 1 Ma- nure only (1) Ratio ML M (2) Ma- nure only (3) Ratio ML M (4) Ma- nure only (5) Ratio ML M (6) Ma- nure only (7) Ratio ML M (8) I. Dark soils with heavy, noncal- bu. 28.4 38.9 34.5 33.4 33.8 32.5 39.6 27.3 28.9 28.1 24.6 24.2 23.1 24.9 23.2 23.9 12.7 8.4 8.7 8.5 12.3 13.2 7.3 9.2 2.0 5.9 8.3 6.9 1.194 1.018 1.052 .952 1.047 1.083 1.002 1.198 1.104 1.149 1.163 1.161 1.169 1.177 1.293 1.197 1.504 1.786 2.287 2.047 1.683 1.894 2.699 2.065 6.600 3.830 2.410 2.029 bu. 56.6 58.5 68.9 58.8 60.7 66.5 46.4 58.8 57.3 58.0 39.0 44.7 53.6 38.2 37.9 43.6 25.4 20.5 22.9 21.7 29.4 28.2 26.9 18.1 16.4 22.3 23.5 18.9 1.125 1.018 .996 1.019 1.036 1.069 1.093 1.122 1.086 1.105 1.169 1.203 1.138 1.183 1.203 1.179 1.378 1.424 1.620 1.525 1.401 1.415 1.558 1.591 1.634 1.803 1.549 1.799 bu. 52.7 74.3 67.6 62.4 64.2 71.5 48.0 67.9 64.0 66.0 63.2 43.2 47.2 36.9 42.3 42.4 1.104 .981 1.044 .970 1.020 1.021 1.077 1.053 1.053 1.053 1.027 1.130 1.106 1.119 1.158 1.127 Ions 2.21 2.94 2.37 2.47 2.50 2.24 2.67 2.31 2.30 2.30 1.44 2.32 2.13 2.22 1.83 2.12 .11 .86 .29 .58 .68 .41 .48 .00 .79 .26 .44 .27 1.063 .993 1.101 1.008 1.036 1.053 1.026 1.195 1.070 1.135 1.146 1.121 1.263 1.158 1.481 1.245 13.818 1.488 5.034 2.362 2.368 3.366 2.833 (1.85) 1.519 5.038 3.295 5.111 Hartsburg LaMoille Aledo Average II. Dark soils with noncalcareous subsoils Kewanee III. Brownish-yellow soils with open, noncalcareous subsoils Springvalley IV. Dark soils with open, noncal- careous subsoils Average V. Dark soils with impervious, cal- careous subsoils Joliet VI. Dark soils with impervious, non- calcareous subsoils Carthage Clayton Carlinville Average VII. Sandy loams and sands Oquawka VIII. Yellow soils with noncalcareous subsoils Enfield 17.6 17.6 25.0 19.5 17.2 1.682 1.682 1.336 1.615 1.640 Average IX. Gray soils with impervious, non- calcareous subsoils Toledo Raleigh Sparta Newton 24.4 14.9 20.2 1.443 2.094 1.579 Ewing Average X. Hilly land Elizabethtown . . . Yields on the limed land can be determined by multiplying the yields on the unlimed land by their response ratios. 'Actual yield for limestone. stone are important, and before the full effects of limestone can be realized these deficiencies must be corrected. That the application of manure does tend to correct important soil deficiencies on these soils 1934] RESPONSE OF ILLINOIS SOILS TO LIMESTONE 319 TABLE 6. RESIDUES SYSTEM: RESPONSE OF WHEAT, CORN, OATS, AND HAY TO LIMESTONE ON ILLINOIS SOIL EXPERIMENT FIELDS (Yields are given as annual acre averages) Soil groups and fields in order of natural productivity Wheat yields* Corn yields 1 Oat yields' Hay yields' Resi- dues only (1) Ratio RL R (2) Resi- dues only (3) Ratio RL R (4) Resi- dues only (5) Ratio RL R (6) Resi- dues only (7) Ratio RL R (8) I. Dark soils with heavy, noncal- careous subsoils Hartsburg '. bu. 30.8 37.5 31.2 33.1 33.2 31.8 39.3 24.7 26.1 25.4 22.2 21.0 22.1 21.9 18.4 20.8 12.1 7.4 7.7 7.6 11.3 11.3 10.0 7.7 5.4 1.7 3.4 7.2 4.2 .922 1.056 1.099 .909 .997 1.075 1.023 1.279 1.123 1.197 1.081 1.371 1.204 1.311 1.402 1.317 1.471 2.054 2.338 2.184 1.726 2.000 1.870 2.143 3.315 5.582 5.912 2.472 2.405 bu. 69.2 53.3 62.8 57.7 59.2 59.0 47.8 50.8 49.3 50.0 33.8 49.2 47.6 34.2 33.2 41.0 20.8 16.2 19.0 17.6 24.5 18.5 20.6 18.3 15.2 10.3 12.3 17.1 14.7 1.052 1.073 1.123 1.036 1.071 1.139 1.040 1.232 1.156 1.196 1.151 1.201 1.220 1.374 1.223 1.254 1.745 1.969 1.731 1.841 1.269 1.405 1.209 1.891 1.586 1.650 2.049 1.526 2.170 bu. 50.2 69.8 70.8 61.4 63.0 61.1 48.7 58.3 57.9 55.9 55.9 52.2 52.9 41.4 39.8 46.5 .972 1.063 1.047 1.020 1.030 1.083 1.121 1.294 1.173 1.231 1.061 1.130 1.191 1.488 1.314 1.267 tons 2.00 2.00 1.82 1.75 1.89 1.38 2.33 1.57 1.54 1.56 .99 1.53 1.62 1.26 1.96 1.59 .11 .59 .18 .38 .63 .37 .40 .28 .00 .55 .21 .35 .16 .995 1.045 1.000 .966 l.OOO 1.174 1.030 1.293 1.130 1.211 1.162 1.248 1.377 1.294 1.316 1.314 13.364 1.458 6.722 2.710 2.286 3.594 2.650 2.929 (1. 39') 1.727 4.905 3.296 2.938 LaMoille \ledo Average -. II. Dark soils with noncalcareous subsoils III. Brownish-yellow soils with open, noncalcareous subsoils IV. Dark soils with open, noncal- careous subsoils V. Dark soils with impervious, cal- careous subsoils Joliet VI. Dark soils with impervious, non- calcareous subscils Carthage Clayton Carlinville Average VII. Sandy loams and sands VIII. Yellow soils with noncalcareous subsoils. Enfield 16.9 16.9 32.3 17.3 2.308 2.308 1.542 2.058 IX. Gray soils with impervious, non- calcareous subsoils Odin Raleigh 16.8 1.869 Sparta Newton 17.0 15.8 19.8 2.006 2.297 1.889 X. Hilly land 'Yields on the limed land can be determined by multiplying the yields on the unlimed land by their response ratios. 'Actual yield for limestone. and hence to make possible a greater response to limestone is con- firmed by a comparison of the long-time crop yields and the yields of the last rotation. In the manure system every field in the light-colored 320 BULLETIN No. 405 [June, group, with the exception of the Elizabethtown field, has given a greater response to limestone during the last rotation than during the complete period of experimentation, a fact that indicates the increas- ing value of limestone applications. In the residues system only four fields in the light-colored group show such increases and some have FIG. 6. LIMESTONE IMPROVES BOTH YIELD AND QUALITY OF CORN The acre-yield of corn where the land was treated with manure and lime- stone was 49.1 bushels, and 11.3 bushels were reasonably sound ears. The total yield on the land receiving only manure was 35.1 bushels, and only 3.3 bushels were reasonably sound. Toledo- field, 1933. shown rather large decreases. Experiments indicate that the fields in the light-colored group are deficient in potash, a deficiency which manure corrects. Wheat The influence of limestone on wheat yields (Fig. 7) is, in general, similar to its influence on corn yields (Fig. 4), the light-colored, less productive soils giving larger increases than the dark-colored, more productive soils. Within the major soil groups, moreover, there is a variation in response among the different fields, the naturally less productive fields showing the greatest increases in yields. Wheat in- 1934} RESPONSE OF ILLINOIS SOILS TO LIMESTONE 321 creases from limestone application have been smaller, however, than corn increases. On the more productive dark-colored soils the wheat increases have been negligible. Wheat grown on light-colored soils has been especially responsive to limestone in the residues system, a noticeable contrast to the re- S * DARK-COLORED SOILS LIGHT-COLORED SOILS LIMESTONE AND CROP RESIDUES $ 9 DARK-COLORED SOILS LIGHT-COLORED SOILS FIG. 7. INFLUENCE OF LIMESTONE ON WHEAT YIELDS Wheat is not strikingly responsive to limestone on dark-colored soils as a group, but on light-colored soils it tends to be much more responsive than corn. sponse of corn under similar conditions. During the last rotation period all the fields on light-colored soils except four gave an average annual increase that was larger than the increase for the longer period. Apparently other soil deficiencies, such as a low supply of potash, do not check wheat yields so much as they do corn yields. On the 322 BULLETIN No. 405 [June, Raleigh field, however, soil deficiencies other than limestone have re- tarded the yields during the last rotation period. FIG. 8. ON LAND OF Low PRODUCTIVITY WHEAT YIELDS ARE LIKELY TO BE VERY POOR WITHOUT LIMESTONE With manure alone, only 1 bushel of wheat was produced on the above field. Twenty-four bushels were harvested on land that had received both limestone and manure. Neivton field, 1930. FIG. 9. WHEAT YIELDS ON SAND LAND WERE MORE THAN DOUBLED BY LIMESTONE The unlimed field yielded at the rate of 15 bushels of wheat an acre. The limed field produced 35 bushels an acre. Oquawka field, 1930. 1934} RESPONSE OF ILLINOIS SOILS TO LIMESTONE Oats 323 The influence of limestone on oat yields has been most marked on the light-colored soils, especially in the residues system (Fig. 10). In the manure system, however, limestone has tended to be less effective FIG. 10. INFLUENCE OF LIMESTONE ON OAT YIELDS Limestone has produced greater increases in yields of oats on the light- colored soils than on the dark-colored soils. On both groups of soils the residues system has given better results than the manure system. on all fields. On the dark-colored soils as a group it was relatively ineffective. In general the oat rotation yields, compared with long- time yields, reveal increasing responses, especially in the light-colored group. There is no particular evidence that the response of the oat 324 BULLETIN No. 405 [June, crop has been interfered with, especially, by deficiencies of other nutrients. On the whole, oats appear to be less responsive to limestone than either corn or wheat. Hay Crops Study of the influences of limestone on the growth and yield of hay is somewhat complicated by the fact that the same hay crops were not used on all fields. On many of the dark-colored soils red clover LIMESTONE AND MANURE FIG. 11. INFLUENCE OF LIMESTONE ON HAY CROPS Limestone applications have increased hay yields in about the same way as they have the grain yields. In the manure system, increases during the last rotation have tended to be larger than during the longer period. In the residues system this tendency has not been so apparent, the absence of other nutrients making it impossible for limestone to become fully effective. 1934} RESPONSE OF ILLINOIS SOILS TO LIMESTONE 325 was the usual hay crop grown, on some fields alfalfa was grown, and on others a mixture of red clover and alfalfa was used. In recent years a mixture of alsike clover, red clover, alfalfa, and timothy has been used on the light-colored soils. In the earlier years alsike and red clover were used alone. When the hay crops have failed, soybeans have usually been substituted. FIG. 12. LIMESTONE MAKES GOOD HAY YIELDS POSSIBLE ON SOILS OF Low NATURAL PRODUCTIVITY A mixed hay seeding produced no crop where only manure was applied. It yielded over 2 tons of good hay an acre on the land that received limestone and manure. The mixed hay contained considerable alfalfa. Enfield field, 1931. The largest responses of harvested hay crops to limestone have been obtained on the light-colored soils (Figs. 11 and 12). Rather low responses have been obtained on a number of the dark-colored soils. Limestone has thus affected the hay crops in a way somewhat similar to the way in which it has affected the grain crops. In general the average annual increases in weight of crop ma- terials during the last rotation, in both the residues and the manure systems, are as great as those obtained for the longer period, or greater. In the manure system, especially, the response has been favorable during the last rotation ; but in the residues system the re- sponse for the last rotation has been similar to that for the longer period. The slowing up of the response in the residues system prob- ably indicates a deficiency of nutrients not supplied by limestone or crop residues. On the whole the response of the hay crops to limestone has been 326 BULLETIN No. 405 [June, sufficiently favorable to indicate the need of limestone for hay pro- duction on many Illinois soils. Comparative Responses of Above Crops The relative importance of limestone for wheat, corn, oats, and hay is indicated by the data recorded in Tables 5 and 6 and Fig. 13. The crop yields are given for the unlimed land, and the influence of 240 200 160 eo 4C I MANURE SYSTEM %Z& RESIDUES SYSTEM WHEAT CORN OATS HAY DARK-COLORED SOILS WHEAT CORN HAY SAND SOILS WHEAT CORN OATS HAY LIGHT-COLORED SOILS FIG. 13. COMPARATIVE RESPONSE OK WHEAT, CORN, OATS, AND HAY TO LIMESTONE APPLICATIONS On dark-colored soils the responses of the various kinds of crops have been somewhat similar, tho oats have tended to be the least responsive. AH crops have been more responsive on sandy soils than on other soils, the hay crops being very responsive. On the light-colored soils the grain crops are much more responsive than on the other kinds of soil. Wheat is about twice as responsive as corn on these soils. The hay crops are highly responsive but less so than when grown on sandy soils. limestone is recorded as a ratio between the limed and the unlimed yields. If the yield for the limed land is desired, it can be determined by multiplying the unlimed yield by the ratio figure. Thus if the yield of corn was 30 bushels an acre on unlimed land and the response ratio was 1.500, it would mean that the yield on the limed land was 45 bushels (30 X 1.500). 79J-/] RESPONSE OF ILLINOIS SOILS TO LIMESTONE 327 For all crops limestone has demonstrated its importance much more strikingly on the sandy and the light-colored soils than on the dark-colored soils. The hay crops are especially responsive on the sandy and the light-colored soils. The grain crops differ more in their response to limestone on these soils than they do on the dark-colored soils. Wheat, for example, is much more responsive than corn on the light-colored soils, but on the more productive dark-colored soils the difference is negligible. All crops, however, have given a rather small response to limestone on the dark-colored soils. Oats usually have given the smallest response of any of the nonlegume crops on these soils. In general, crop responses to limestone have been greater in the residues system than in the manure system. Responses of Legume Crops The response of soybeans, common clovers, and alfalfa to lime- stone applications, in both the manure and residues systems, is shown in Tables 7 and 8. Since these legume crops were not grown regu- larly on all fields, it is impossible to make comparisons of their in- dividual responses under all soil conditions, but nevertheless some in- teresting differences in these crops are to be observed. Altho all the legumes grown on light-colored soils gave a re- markable response to liming, the common clovers gave a much more pronounced response than soybeans. The increase in the yield of the FIG. 14. LIMESTONE MEANS A BETTER FIRST-YEAR STAND OF RED CLOVER Seeded in the spring with oats, red clover made very sparse growth on land where only manure was applied. The above pictures were taken in the fall of the first year. A year later the hay yield on the limed land was three- quarters of a ton larger than on the unlimed land. Mi. Morris field, 1932. 328 BULLETIN No. 405 [June, clovers varied from 300 to 465 percent, while that of the soybeans varied from 37 to 66 percent. Legumes grown on the most productive fields gave but little re- sponse to limestone and varied little in their degrees of response. On the dark-colored soils of medium and low productivity (Groups IV, V, and VI) the various legumes showed rather striking differences in their response to limestone. Soybean increases varied from 4 to 10 FIG. 15.- -LiMEsxoNE MAKES THE DIFFERENCE BETWEEN- ALFALFA AND No ALFALFA ON SANDY LAND Limestone and alfalfa are an excellent combination for sandy land. Three and a quarter tons of good quality alfalfa hay was harvested where limestone and manure were applied. On land that received only manure, alfalfa failed completely. Oquaicka field, 1931. percent, while increases in the yields of the common clovers varied from 14 to 40 percent. On both the light-colored and the dark-colored soils the greatest increases were obtained in the residues system. The variations in the responses of the various kinds of crops legumes and nonlegumes to limestone, are, no doubt, related to their lime requirements and the ease with which they are able to obtain the needed lime from the supplies naturally in the soil. The lime deficien- cies in the dark-colored soils are not sufficient to cause a great deal of difference in the growth of the different kinds of crops except clover and alfalfa when grown on some of the least productive soils in these groups. In the sandy and the light-colored soils the available calcium or other lime materials and other nutrients are sufficiently low to cause somewhat more striking differences in the responses of the different crops. 1934] RESPONSE OF ILLINOIS SOILS TO LIMESTONE 329 TABLE 7. MANURE SYSTEM: RESPONSE OF SOYBEANS, CLOVER, AND ALFALFA TO LIMESTONE ON ILLINOIS SOIL EXPERIMENT FIELDS (Yields are given as annual acre averages) Soil groups and fields in order of natural productivity Soybean yields 1 Clover yields' l Alfalfa yields' No. of crops (1) Ma- nure only (2) Ratio ML M (3) No. of crops (4) Ma- nure only (5) Ratio ML M (6) No. of crops (7) Ma- nure only (8) Ratio ML M (9) I . Dark soils with heavy, non- calcareous subsoils Hartsburg 2 1 3 4 tons 1.64 2.20 1.92 1.51 1.73 1.110 .991 1.047 1.060 1.056 6 8 6 5 14 13 15 13 12 14 14 8 11 2 tons 2.40 3.03 2.74 2.81 2.76 2.24 2.67 2.40 2.33 2.37 1.45 2.30 2.13 2.95 2.00 2.29 .00 1.042 .993 1.139 .975 1.034 1.053 1.026 1.204 1.069 1.142 1.159 .213 .324 .156 .635 .318 (3.52<) 10 11 tons 3.67 2.55 1.065 1.008 LaMoille Aledo 3.08 1.040 II. Dark soils with noncal- careous subsoils III. Brownish-yellow soils with open, noncal- careous subsoils 1 2 5 2.47 1.80 1.75 1.76 1.51 2.12 1.84 1.59 1.76 1.79 1.03 .95 .59 .88 1.25 .72 .91 .69 .83 .48 .79 .50 1.032 .978 1.069 1.042 1.086 .000 .087 .151 .142 .096 1.146 1.537 2.169 1.626 1.528 1.764 1.516 1.826 1.410 2.500 1.655 1.480 8 12 24 13 3.30 2.33 3.95 3.41 1.35 1.142 1.601 1.109 1.221 1.437 IV. Dark soils with open, non- calcareous subsoils Mt. Morris Average* V. Dark soils with impervi- ous, calcareous sub- soils Joliet 6 5 5 9 4 VI. Dark soils with impervi- ous, noncalcareous subsoils Clayton Carlinville VII. Sandy loams and sands 17 19 5 14 1.68 1.738 VIII. Yellow soils with noncal- careous subsoils Unionville Hnli.-lil 2 4 3 9 1 .27 .27 .46 .24 .25 .00 4.410 4.410 2.696 3.250 5.280 (1.66*) IX. Cray soils with impervi- ous, noncalcareous subsoils Oblong 5 3 8 15 17 8 Toledo Raleigh Sparta Newton Ewing 3 .23 .27 4.565 4.322 Average 1 X. Hilly land Elizabethtown 4 6 .10 11.900 Yields on the limed land can be determined by multiplying the yields on the unlimed land by their response ratios. 'Mostly red clover. 'Weighted averages. 4 Actual yield for limestone. 330 BULLETIN No. 405 [June, TABLE 8. RESIDUES SYSTEM: RESPONSE OF SOYBEANS, CLOVER, AND ALFALFA TO LIMESTONE ON ILLINOIS SOIL EXPERIMENT FIELDS (Yields are given as annual acre averages) Soil groups and fields in order of natural productivity Soybean yields 1 Clover yields 1 Alfalfa yields 1 No. of crops (1) Resi- dues only (2) Ratio RL R (3) No. of crops (4) Resi- dues only (5) Ratio RL R (6) No. of crops (7) Resi- dues only (8) Ratio RL R (9) I . Dark soils with heavy, non- calcareous subsoils Hartsburg 3 2 4 5 bu. 25.4 17.2 16.0 18.6 19.1 1.024 1.035 1.062 .952 1.009 6 8 6 5 14 13 15 13 12 14 14 8 11 2 tons .78 .94 .91 .50 .81 1.38 2.33 1.57 1.48 1.53 .97 1.36 1.48 1.48 1.83 1.53 .00 .955 1.041 .937 1.007 .989 1.174 1.030 1.306 1.176 1.247 1.155 1.360 1.385 1.344 1.497 1.403 (2.13*) 10 tons 3.78 .913 LaMoille Aledo 3.78 .913 11. Dark soils with noncal- careous subsoils III. Brownish-yellow soils with open, noncal- careous subsoils 1 2 6 22.8 16.0 14.0 14.5 13.1 23.7 17.6 14.0 17.6 17.4 8.5 5.9 3.8 5.4 10.5 5.3 8.2 5.7 4.9 5.4 3.4 6.4 2.7 .991 1.181 1.014 1.060 1.092 .932 1.125 1.086 1.290 1.085 1.435 1.441 2.500 1.612 1.495 1.830 1.268 2.123 2.367 1.611 2.823 1.667 1.370 IV. Dark soils with open, non- calcareous subsoils V. Dark soils with impervi- ous, calcareous sub- soils Joliet 11 5 5 10 4 13 1.12 1.393 VI. Dark soils with impervi- ous, noncalcareous subsoils Carthage Clayton Carlinville Average 1 14 1.36 2.147 VII Sandy loams and sands Oquawka 18 20 6 VIII. Yellow soils with noncal- careous subsoils Enfield 2 4 3 .17 .17 .60 .15 4.765 4.765 2.650 7.267 Average 2 IX. Gray soilswith impervious, noncalcareous sub- soils Oblong 6 5 26 8 13 18 8 Toledo . Odin Raleigh 9 1 .08 .00 8.875 (1-50) 3 .00 .18 (.88') 5.647 X. Hilly land 5 6 .02 34.000 >Yields on the limed land can be determined by multiplying the yields on the unlimed land by their response ratios. 'Weighted averages. 'Actual yield for limestone. 1934] RESPONSE OF ILLINOIS SOILS TO LIMESTONE 331 That the various crops have made less pronounced responses to limestone in the manure system than in the residues system is due to the effect of the manure in reducing deficiencies of lime and other plant nutrients. EFFECT OF LIMESTONE ON SOIL PRODUCTIVITY LEVELS The soils upon which the different experiment fields are located vary greatly in natural productiveness (Table 1). The more produc- tive soils yield, on the average, more than a ton and a quarter of grain and hay an acre annually, corn alone averaging about 50 bushels an acre. The poorest soils are only about one-tenth as productive. The Elizabethtown field, for instance, produces on the average only 325 pounds of grain and hay an acre annually and 11.5 bushels of corn. The other soils produce yields distributed more or less uniformly be- tween these extremes. Whether the level of productivity of the poorer soils can be raised to that of the naturally more productive soils by means of good management and treatment practices is a question of very practical interest. The direct influence of limestone on the productive levels of the different soils is shown in Table 9 and also in Tables 1 and 4. The fields in Soil Group I are used as the standard of reference. The annual crop yields of the untreated land in this group have averaged 2,477 pounds an acre. The field representing Group X, the least pro- ductive group, has produced only 325 pounds an acre, or 13.1 percent as much as the average in Group I. The ratio is then .131. The total yields from the limestone plots in both the manure and the residues systems divided by 2,477 provide ratios (Columns 4 and 6) which indicate directly the influence that limestone has had in raising the productivity levels of the various soils toward the levels of the naturally more productive soils. The results for the different soil groups are shown graphically in Fig. 16. Limestone has raised the productivity levels of all soils. It has shown the least influence on the naturally more productive soils and the greatest influence on the naturally less productive soils. The handi- cap on the least productive soils, however, is so great that the present levels are far from approaching the natural levels of the more pro- ductive soils. The light-colored soils have, under treatment, reached production levels that are approximately 50 percent as high as the levels of the naturally more productive soils. Groups II, III, and IV, 332 BULLETIN No. 405 [June, representing the more productive dark-colored soils, are the only groups whose levels have been raised to that of Group I, the standard used. On the dark-colored soils limestone used in the residues system tended to be more effective than in the manure system. This tendency, however, was reversed on the sandy and the light-colored soils. 120 100 UNTREATED LAND RESIDUES SYSTEM MANURE SYSTEM IZ T TZI SOIL GROUPS "VTT VTIT TT FIG. 16. INFLUENCE OF LIMESTONE ON PRODUCTIVITY LEVELS OF VARIOUS ILLINOIS SOILS The productivity levels of Groups II to X, compared with that of Group I, the naturally most productive soils, without soil treatment, are shown by the lower portions of the bars. The influence that limestone has had in raising the productivity levels of these soils, both in the manure and in the residues systems of farming, is shown by the upper parts of these bars. Limestone raised the level of every group, Groups II, III, and IV reaching the 100-percent level. The least productive soils were raised approximately to 50 percent of the level of the most productive soils. Thus limestone has had striking effects in raising the productive levels of some soils, but it has not been able to bring all soils to the same level. 1934] RESPONSE OF ILLINOIS SOILS TO LIMKSTONE 333 TABLE 9. INFLUENCE OF LIMESTONE ON PRODUCTIVE LEVELS OF ILLINOIS SOILS Soil groups and fields in order of natural productivity Untreated land Limed land Aver- age yield (1) Produc- tivity ratio 1 (2) Manure system Residues system Yield (3) Produc- tivity ratio' (4) Yield (5) Produc- tivity ratio' (6) I. Dark soils with heavy, noncalcareous subsoils Ibs. 2 600 2 524 2 396 2 388 2 477 2 408 2 372 2 210 2 068 2 139 1 690 1 748 1 723 1 661 1 476 1 652 799 684 494 589 731 611 608 558 527 500 482 574 325 1.050 1.019 .967 .964 1.000 .972 .958 .892 .835 .863 .682 .706 .696 .670 .596 .667 .322 .276 .199 .238 .295 .247 .246 .225 .213 .202 .194 .232 .131 Ibs. 2 916 2 547 2 702 2 378 2 636 2 546 2 494 2 527 2 283 2 405 2 045 2 117 2 185 1 941 2 170 2 103 1 747 1 148 1 418 1 283 1 511 1 403 1.177 1.028 1.098 .960 1.064 1.028 1.007 1.020 .922 .971 .826 .855 .882 .784 .876 .849 .705 .463 .572 .518 .610 .566 Ibs. 2 548 2 670 2 615 2 382 2 554 2 670 2 484 2 747 2 331 2 539 1 946 2 222 2 279 2 075 2 014 2 147 1 593 1 124 1 131 1 128 1 238 1 228 872 1 241 1 010 969 1 150 1 101 934 1.029 1.078 1.056 .962 1.031 1.078 1.003 1.109 .941 1.025 .786 .897 .920 .838 .813 .867 .643 .454 .457 .455 .500 .455 .352 .501 .408 .391 .464 .444 .377 LaMoille Aledo II. Dark soils with noncalcareous subsoils III. Brownish-yellow soils with open, noncalcare- ous subsoils IV. Dark soils with open, noncalcareous subsoils Average V. Dark soils with impervious, calcareous subsoils Joliet VI. Dark soils with impervious, noncalcareous subsoils Carthage Carlinville VII. Sandy loams and sands VIII. Yellow soils with noncalcareous subsoils Enfield IX. Gray soils with impervious, noncalcareous subsoils Oblong Toledo Odin Raleigh 1 442 1 248 1 179 1 506 1 381 1 091 .582 .504 .476 .608 .558 .440 Sparta Newton Ewing Average X. Hilly land Eliza bethtown. . . 'The ratio representing the productive level of a field is obtained by dividing the average annual e-yield by 2,477, the average yield (in pounds) of the more productive soils (Group I). 334 BULLETIN No. 405 [June, RAPIDITY AND TREND OF RESPONSE TO LIMESTONE In the preceding pages the discussion dealt with the influence of limestone on crop yields as revealed by data massed into rather broad averages averages for all the years since limestone applications were started. Data massed in this way reveal certain outstanding facts, but they do not show how quickly crop increases were obtained on the different fields and soils, nor whether such increases became greater, remained the same, or diminished with the passage of time matters of very great importance to all interested in the use of limestone for soil-improvement purposes. 600 400 200 400 200 -200 400 200 -200 200 -200 200 -200 -HARTSBURG -LAMOILLE CROUP AVERAGE Fic. 17. TREND OF LIMESTONE INFLUENCE ON DARK SOILS WITH HEAVY, NONCALCAREOUS SUBSOILS, GROUP I There is some evidence that limestone has tended to be of a little more value in recent years than in the earlier years of these experiments. In order to ascertain the rapidity and the trend of the response to limestone exhibited by different soils under different systems of farm- ing, the yearly increases in crop yields on the various fields under the manure and residues systems of farming have been converted into movable rotation averages and plotted into the graphs shown in 19341 RESPONSE OF ILLINOIS SOILS TO LIMESTONE 335 Figs. 17 to 22. Since a four-year rotation is practiced on most fields, the figure for any particular year is the average of sixteen crop harvests. The small figures along the zero line in the trend charts for each individual field represent tons of limestone applied for that field and approximate time of application. The total tonnage of limestone for each field can be determined by adding together the figures given for that field. Dark Soils With Heavy, Noncalcareous Subsoils The rapidity and the trend of the response to limestone on the fields in the most productive soil groups the dark soils with heavy, noncalcareous subsoils (Group I) have not been striking (Fig. 17). The best response has been obtained on the Aledo field, especially in the residues system, where the crop increases resulting from lime- stone applications have tended to become gradually larger. The Mi- nonk field has never given much response to limestone. On all fields except the one at Hartsburg better responses have been obtained in the residues system than in the manure system. No reason has been discovered for the peculiar behavior of the Hartsburg field. When the responses for all fields are averaged together for each year, there is a slight tendency for the later years to show the greater response. This increasing response suggests that these soils are be- coming deficient in lime, and that with continued cultivation of this land limestone may come to be of more and more importance. Dark Soils With Open, Noncalcareous Subsoils On the Mt. Morris and the Dixon fields, representing the dark soils with open, noncalcareous subsoils (Group IV), the increases from the use of limestone were rather small during the earlier years these fields were under test (Fig. 18). After the first two rotations, however, there were pronounced increases in yields, which were main- tained for about twelve years. For the last three or four years there has been a falling off in response, indicating either the need for further applications of limestone or an increasing deficiency of some other nutrient. Field tests show no deficiency of lime. As in Group I, the dark soils with heavy, noncalcareous subsoils, the greatest responses to limestone have been obtained in the residues system. Dark Soils With Impervious, Noncalcareous Subsoils Steadily increasing yields from the use of limestone were obtained on the Carthage, Clayton, Lebanon, and Carlinville fields, representing 336 BULLETIN No. 405 [June, the dark soils with impervious, noncalcareous subsoils (Group VI), for the first fifteen or sixteen years these fields were under test (Fig. 19). For the last six or seven years, however, increases in yield have tended to remain stationary on some fields and on others have declined. On three fields Carthage, Clayton, and Lebanon the largest increases have been obtained in the residues system. During recent years, however, the manure and residues systems have tended to be- 600 40O 200 -200 600 600 400 200 00 -200 800 eoo 400 200 -200 -GROUP AVERAGE FIG. 18. TREND OF LIMESTONE INFLUENCE ON DARK SOILS WITH NONCALCAREOUS SUBSOILS, GROUP IV The response to limestone was low in the early years. It became increas- ingly larger in later years, reaching the crest of its influence after about six- teen years, since which time it has been slowly receding. come about equally effective. In fact, on the Clayton field in 1931 the response in the manure system was slightly higher than in the residues system. On the Carlinville field the advantage has always been with the manure system. On this field, the soil of which is in a later stage of development than that of the other three fields (see Table 1), manure is evidently supplying a deficiency that is becoming more and more pronounced and that cannot be cared for in the residues system. Experiments on the Carlinville field indicate that this deficiency may be potassium. 1934] RESPONSE OF ILLINOIS SOILS TO LIMESTONE 337 Fir.. 19. TREND OF LIMESTONE INFLUENCE ON DARK SOILS WITH IMPERVIOUS, NONCALCAREOUS SUBSOILS, GROUP VI More or less regular increases in crop yields have occurred on the fields in this soil group since the beginning of the limestone applications. Limestone reached the crest of its influence about eighteen years after the first application, since which time it has gradually declined. 338 BULLETIN No. 405 [June, Yellow Soils With Noncalcareous Subsoils The Enfield and Unionville fields, representing the yellow soils with noncalcareous subsoils (Group VIII), have shown quite different responses to limestone (Fig. 20). 1910 1913 1916 1919 1922 1925 1928 1931 FIG. 20. TREND OF LIMESTONE INFLUENCE ON YELLOW SOILS WITH NONCALCAREOUS SUBSOILS, GROUP VIII The Enfield field has shown a rapidly increasing response to limestone thruout practically the twenty years of test. The Unionville' field showed a gradually increasing response during the first years, but during the last fifteen years the response has remained practically stationary. The differences between these fields in their responses to lime- stone are doubtless due to differences in certain soil characteristics. The Unionville field is located close to the Ohio river in Massac county on comparatively low land, whereas the Enfield field is away from the river on higher land. On both fields better responses to limestone have appeared in the manure system than in the residues system. 1934} RESPONSE OF ILLINOIS SOILS TO LIMESTONE 339 Gray Soils With Impervious, Noncalcareous Subsoils Fairly rapid and increasing responses to limestone have been shown by the gray soils with impervious, noncalcareous subsoils (Group IX), represented by seven fields the Ewing, Oblong, Newton, Odin, 1910 1913 1916 1919 1922 1925 1926 1931 Fu.. 21. TREND OF LIMESTONE INFLUENCE ON GRAY SOILS (GROUP IX) Raleigh, Toledo, and Sparta fields (Fig. 21). The Ewing field has given the most striking response, the Odin field the least striking. The greatest responses have occurred in the manure system, 340 BULLETIN No. 405 [June, especially on the Ewing field, where the trend has been upward with no indication that the limit of response has been reached. In the residues system on the Ewing field a rapidly increasing response to 1910 1913 1919 1919 1922 1925 1928 1931 FIG. 21. CONCLUDED On the whole the fields representing this soil group have shown a rapid upward trend in their response to limestone applications. In all groups lime- stone has been decidedly more effective when used with manure than when used with crop residues. Some fields are continuing to show increasing response ; some are leveling out ; and some are declining. limestone occurred during the first eight years, since which time there has been but little change in the response level. On the other fields in this group the differences between the ma- nure and the residues systems in their responses to limestone are 1934] RESPONSE OF ILLINOIS SOILS TO LIMESTONE 341 similar to the differences on the Evving field. Other experiments on these fields indicate that there may be a deficiency of potash, a deficiency that manure would help to correct. If the manure system had been used on the Odin field, the results would probably have been similar to those in the manure system on the Ewing field. On the whole, limestone has proved of great importance to the soils in this group. Other Soils Represented by Single Fields The limestone responses for each of the five soil groups repre- sented by only one field are shown in Fig. 22. The dark-colored soils, represented by the Joliet, Kewanee, and Springvalley fields, have given relatively small responses to lime- stone. On the Springvalley field there have been practically no crop increases, while on the Joliet and Kewanee fields there have been slowly increasing yields. The sandy and the hilly lands, represented by the Oquawka and Elizabethtown fields, have given very favorable responses to lime- stone. This is especially true of the sandy Oquawka field, which, during the first eight years of the test, gave the most rapid response of all the fields studied. During the last nine years crop yields have tended to remain stationary or to decline slightly, suggesting that limestone is possibly decreasing in its effectiveness. The hilly land at Elizabethtown also responded very rapidly at first to limestone ap- plications, but here too, after eight years, crop yields have tended to remain stationary or to decline. General Discussion of Response Trends As indicated in the foregoing graphs, different soils vary con- siderably in the rapidity of their response to limestone and in the degree of their response. The more productive, dark-colored soils (Group I), on the whole, have given rather small increases in crop yields as a result of limestone applications. Two fields in this group that produced good crops for many years without showing much response to limestone have begun to give increased yields for lime- stone, a fact which indicates that they are becoming lime-deficient. From now on they are likely to give increasing responses to limestone. On all the other dark-colored soils the crop increases in recent years have tended to remain stationary and on some fields even to decline. This slowing up of response may hint that other nutrients are becoming deficient and that such deficiencies are interfering with 342 BULLETIN No. 405 [June, the effects of limestone. That other nutrients are becoming deficient in the dark-colored soils is indicated by the differences in response to limestone in the manure and in the residues systems. On the more productive dark-colored soils the response in the residues system has DARK SOIL WITH IMPERVIOUS CALCAREOUS SUBSOIL BROWNISH YELLOW SOILS WITH OPEN NONCALCAREOUS SUBSOILS FIG. 22. TREND OF LIMESTONE INFLUENCE ON SOIL GROUPS REPRESENTED BY A SINGLE FIELD No very definite responses have been exhibited by the Joliet, Kewanee, and Springvalley fields, representing Groups II, III, and V. The Oquawka and Elizabethtown fields, representing Groups VII and X, however, showed rather rapid response for the first ten years, and these responses reached rather high levels. been as great as that in the manure system, or greater. On the less productive dark-colored soils the advantage in favor of the residues system has tended to disappear. On the sandy and the light-colored soils the advantages have been decidedly in favor of the manure sys- 1934] RESPONSE OF ILLINOIS SOILS TO LIMESTONE 343 tern. Evidently the legume-limestone system of soil management is not so effective in meeting the requirements of the less productive soils as is the manure-limestone system. Deficiencies in phosphorus or potassium, or both, are met in part at least by the manure applied. Tho nutrients other than phosphorus and potassium may also be in- volved, experiments indicate that on some fields Joliet and Eliza- bethtown, for example the deficient element probably is phosphorus. On the light-colored soils, such as those represented by the Ewing, Toledo, and other fields, there is apparently a deficiency of potassium. Where either deficiency exists, the effectiveness of limestone is likely to be reduced until the deficiency is corrected. Lasting Effects of Single Applications of Limestone The West Salem field (a mature yellow soil with noncalcareous subsoil, Group VIII), not represented in the above summaries, pro- vides data that show the long-time response that may result from a single application of limestone. In 1912 limestone at the rate of 4 600 600 400 200 SINGLE APPLICATION REPEATED WITH MANURE REPEATED WITH RESIDUES 1912 1916 1920 1924 1928 1932 FIG. 23. LASTING EFFECTS OF A SINGLE APPLICATION OF LIMESTONE AS SHOWN BY INCREASES IN CROP YIELDS A 4-ton application of limestone was made to certain plots on the West Salem field in 1912. One of these plots received no further limestone. The greatest increase in crop yields on this plot occurred in 1919, the eighth year after the limestone application, and it is apparent that this one application is still having an effect. The crops grown were corn, oats, wheat, and hay in rotation. 344 BULLETIN No. 405 [June, tons an acre was applied to each of three plots that were originally designed for crop production without limestone. One of these plots has never received any further treatment; another has received ma- nure only; and a third has received crop residues only. Similar plots receiving regular applications of limestone were maintained alongside the above plots until 1923, when limestone applications were tempo- rarily discontinued on all plots. The lasting effect of a single application of limestone without manure or residues, over a twenty-year period, is indicated by the solid line in Fig. 23. The single application steadily increased crop yields until the eighth year. During the eighth and ninth years the increases remained about stationary, but after the ninth year they grew steadily smaller. After twenty years, however, there is still evidence of a decided influence from the single application of limestone. The repeated applications of limestone in the manure and residues systems showed little superiority over the single application until the eighth year, after which they gave much better results. Apparently a second application of limestone to soils of this type is not needed until about eight years after the initial application. The increases in yields resulting from the repeated applications of limestone, even tho none have been made since 1923, still show a steady upward trend. Response Trends as Related to Total Yields In studying only the spreads between total yields on treated land and total yields on comparable untreated land the question arises whether the differences are the result of definite improvement in the productive level of the treated land or of the declining productivity of the untreated land. This question is answered in Fig. 24 for two groups of Illinois soils Group VI, the dark soils with impervious, noncalcareous subsoils, and Group IX, the gray soils with impervious, noncalcareous subsoils. The increases arising from the application of limestone to these soils were, without exception, the result of improved crop yields on the limed land and not of declining yields on the unlimed land. On some fields the yields from the unlimed land tended to remain about the same year after year ; on other fields they tended to become larger but at a slower rate than those obtained from the limed land. On no field was there any tendency for the yields on the limed land to remain stationary while the yields on the unlimed land declined, nor was there any tendency for the yields on the limed land to decline but at a slower rate than on the unlimed land. These statements are also de- 1934] RESPONSE OF ILLINOIS SOILS TO LIMESTONE 345 script! ve of the action of limestone on the fields in the other soil groups studied. Thus the role of limestone in soil management takes on further significance when it is demonstrated that it makes a positive contri- bution to soil productivity rather than merely retarding the process of fertility decline. '200 1910 1913 1916 1919 1922 1925 1928 1931 FIG. 24. CROP YIELDS ON LIMED AND UNLIMED PLOTS OF Two GROUPS OF SOILS UNDER THE MANURE AND CROP RESIDUES SYSTEMS OF TREATMENT That the increases in yields credited to limestone applications on the fields in the above soil groups are the result of definite improvement in yields on the limed land is evident from the fact that the yields on the unlimed land have shown no special tendency to decline. Group VI represents the dark soils with impervious, noncalcareous subsoils, and Group IX the gray soils with the same kind of subsoil. 346 BULLETIN No. 405 [June, ECONOMIC RESPONSES TO LIMESTONE The effects of limestone on various soils, as measured by crop responses, have been shown in the preceding pages without reference to the economic value of such response. A farm practice that has scientific interest is not, however, generally adopted until it becomes clear that it is also economically worth while that is, that it will return a satisfactory margin of profit above all costs. Attempts to generalize concerning the net returns from a given soil treatment over a period of years in such a way that the state- ments have meaning for individual farms are beset with many diffi- culties. Money values must be used, and yet not only are crop prices constantly changing but they vary in different localities, and purchase prices, interest rates, costs of hauling and distributing, and costs of harvesting and marketing the increases in yield vary from farm to farm. Any figures that result from the application of money values to costs and returns must therefore be considered only general indexes of the probable meaning of the practice to an individual farmer. A farmer must refigure costs and returns in accordance with his own experiences before he can know, with a satisfactory degree of accu- racy, the value of a practice to him. Because prices have varied so widely in recent years, three levels of crop prices are used in interpreting, in terms of money values, some of the crop-yield data obtained in these experiments. They represent the average of the higher prices that have prevailed, of medium prices, and of lower prices, as follows: Wheat Higher prices $ 1.25 Medium Lower prices prices $ .88 $ .50 Corn 70 .49 .28 Oats 40 .28 .16 Hav.. 12.50 8.75 5.00 Acre-Values of Crop Increases The value of the increases in crop yields resulting from the use of limestone on Illinois soils, at three levels of crop prices, is indi- cated in Table 10. For most fields approximately two-fifths of a ton, or 800 pounds of limestone (Column 2), may be charged against the annual acre- value of the crop increases. If this amount of limestone should cost around $1.50 applied to the soil, then applications of limestone on the most productive soils (Group I) have not been profitable at any of the 19341 RESPONSE OF ILLINOIS SOILS TO LIMESTONE 347 TABLE 10. AVERAGE ANNUAL ACRE-VALUES OF CROP INCREASES RESULTING FROM USE OF LIMESTONE ON ILLINOIS SOILS (At three levels of prices 1 ) Soil groups and fields in order of natural productivity Limestone applied Value of crop increases in manure system Value of crop increases in residues system Total amount (1) Annual rate (2) At higher crop prices (3) At medium crop prices (4) At lower crop prices (5) At higher crop prices (6) At medium crop prices (7) At lower crop prices (8) I. Dark soils with heavy, non- calcareous subsoils tons 8.50 7.75 8.25 8.25 8.19 6.75 6.75 7.75 8.25 8.00 7.40 7.75 7.75 8.75 9.25 8.37 7.90 8.75 7.75 8.25 8.25 7.25 8.90 9.25 6.75 5.50 9.25 7.88 5.25 tons .42 .41 .41 .41 .41 .40 .40 .41 .41 .41 .41 .41 .41 .42 .42 .41 .44 .42 .41 .41 .41 .38 .30 .42 .42 .29 .42 .38 .37 $3.89 .17 1.96 -.26 1.44 1.67 1.07 4.24 2.46 3.35 3.62 4.03 4.61 4.06 6.47 4.79 8.79 6.63 9.33 7.98 7.45 8.39 $2.72 .12 1.37 -.18 1.01 1.17 .75 2.97 1.72 2.34 2.53 2.82 3.23 2.84 4.53 3.35 6.15 4.64 6.53 5.59 5.21 5.87 $1.55 .07 .79 -.10 .58 .67 .43 1.70 .99 1.34 1.45 1.61 1.85 1.62 2.59 1.92 3.51 2.65 3.73 3.19 2.98 3.36 $-.30 1.89 3.13 -.62 1.02 2.72 1.59 6.48 3.02 4.75 2.84 5.43 5.54 6.12 5.72 5.70 9.06 6.90 8.69 7.80 6.41 7.85 5.04 7.94 9.39 6.18 9.91 7.53 8.01 $-.21 1.32 2.19 -.43 .71 1.90 1.11 4.54 2.11 3.32 1.99 3.80 3.88 4.28 4.00 3.99 6.34 4.83 6.08 5.46 4.49 5.50 3.53 5.56 6.57 4.33 6.94 5.27 5.61 $-.12 .75 1.25 -.25 .41 1.09 .63 2.59 1.21 1.90 1.13 2.17 2.21 2.45 2.29 2.28 3.63 2.76 3.48 3.12 2.56 3.14 2.02 3.17 3.75 2.48 3.96 3.01 3.20 LaMoille : Aledo Minonk Average II. Dark soils with noncalcare- ous subsoils Kewanee III. Brownish-yellow soils with open, noncalcareous subsoils IV. Dark soils with noncalcare- ous subsoils V. Dark soils with impervious, calcareous subsoils Joliet VI. Dark soils with impervious, noncalcareous subsoils Clayton Carlinville VII. Sandy loams and sands Oquawka VIII. Yellow soils with noncal- careous subsoils Enneld IX. Cray soils with impervious, noncalcareous subsoils Oblong Toledo Odin Raleigh 9.15 8.78 8.35 11.19 8.89 8.34 6.40 6.15 5.85 7.83 6.22 5.84 3.66 3.51 3.34 4.47 3.55 3.34 Sparta Newton Average X. Hilly land Elizabethtown . . 'See page 346. BULLETIN No. 405 [June, price-levels used. At the higher crop prices the use of limestone in the manure system has given sufficiently large crop increases to cover this investment, but the margins left to cover the costs of harvesting and marketing the increases in yields and other costs are too small to make the use of limestone profitable on such soils as a group. On the Hartsburg field in the manure system and on the Aledo field in the residues system sufficiently large increases were obtained to justify the use of limestone. On some fields the application of limestone has been a paying practice at the higher crop prices but not at the lower prices. In general, however, all the least productive dark-colored soils, the sandy ET Y 3ZI SOIL GROUPS FIG. 25. ACRE- VALUES OF CROP INCREASES WITH LIMESTONE The various soil groups in the above chart are arranged in descending order of natural productivity. As productivity decreases from one group to another, the acre-value of the crop increases obtained from the use of limestone usually become larger. This tendency for crop increases to grow larger as produc- tivity grows less is not so striking, however, for the sandy and light-colored silt loam soils, all of them giving about the same response regardless of their different natural productivity levels. Evidently there are limits of productivity beyond which it is practically impossible to obtain greater increases for lime- stone. (Based on medium crop prices.) soils, and the light-colored soils have given sufficient increases in crop yields at all price-levels to pay for all additional costs resulting from the use of limestone. The sandy soils and some of the gray soils have given especially favorable economic responses. On the Ewing field in the gray group, for example, the value of the crop increases from limestone in the manure system at the lower prices has averaged nearly $4.50 an acre annually. Such returns should cover all costs involved in the use of limestone and provide a satisfactory profit from its use. RESPONSE OF ILLINOIS SOILS TO LIMESTONE 349 The values of the annual crop increases from limestone, calculated on the basis of the medium crop prices, are shown graphically in Fig. 25 for all the different soils and for both the manure and the residues systems. On the dark-colored soils the residues system gave the greater increase in crop values, while on the light-colored soils the manure system gave the greater increases. The superiority of the manure system on the light-colored soils, as already pointed out, is no doubt due to the value of the manure in correcting certain soil deficiencies that do not exist on the dark-colored soils. Since, as previously shown, the increases that have resulted from limestone, considering all fields and all soil groups, have been, in general, progressively larger from field to field with a decrease in the natural productive levels of these fields, the money values of the crop increases would naturally vary in the same way. Attention is also called again to the fact that in the three soil groups with the lowest productive levels there was little difference in the returns from lime- stone. Ton- Values of Limestone as Measured by Value of Crop Increases The value of the increases in crop yields resulting from each ton of limestone used upon the different experiment fields is indicated in Table 11. The values are based on the three different price-levels stated on page 346. The ton- values of limestone vary greatly on different soils. At the lower prices for crops the average value of a ton of limestone used in the residues system on the more productive dark-colored soils stands at $1.00. On the least productive soils it has proved more than nine times as great as on the more productive dark-colored soils. At the higher prices in the residues system it varies from $2.50 to more than $23 a ton. On the Newton field in the manure system it reaches $28.85. These figures are long-time averages. Values for the last rotation period would be somewhat larger, as is indicated by some of the charts on pages 334-345. The use of limestone has resulted in a margin of return above its cost on most soils. If the average purchase, hauling, and distributing costs should fall somewhere between $3 and $4 a ton, the average values of the increases in crop yields resulting from each ton of lime- stone used would be more than ample to cover all costs involved and still leave a good margin for its use on many fields. Even at the lower prices for crops there is a margin of profit on the majority of 350 BULLETIN No. 405 [June, TABLE 11. VALUES OF CROP INCREASES PER TON OF LIMESTONE USED IN ILLINOIS FIELD EXPERIMENTS (At three levels of crop prices 1 ) Soil groups and fields in order of natural productivity Total lime- stone applied (1) Num- ber of years in- volved (2) Ton-values of limestone in manure system Ton-values of limestone in residues system At higher crop prices (3) At medium crop prices (4) At lower crop prices (5) At higher crop prices (6) At medium crop prices (7) At lower crop prices (8) I. Dark soils with heavy, non- calcareous subsoils tons 8.50 7.75 8.25 8.25 8.19 6.75 6.75 7.75 8.25 8.00 7.40 7.75 7.75 8.75 9.25 8.37 7.90 8.75 7.75 8.25 8.25 7.25 8.90 9.25 6.75 5.50 9.25 7.88 5.25 20 19 20 20 17 17 19 20 18 19 19 21 22 18 21 19 20 19 30 22 16 19 22 14 $9.14 .42 4.76 -.62 3.42 4.20 2.70 10.41 5.96 8.19 8.80 9.87 11.30 9.74 15.40 11.58 20.02 15.90 22.87 19.39 18.06 21.98 $6.40 .29 3.33 -.43 2.39 2.94 1.89 7.29 4.17 5.73 6.16 6.91 7.91 6.82 10.78 8.11 14.01 11.13 16.01 13.57 12.64 15.39 $3.66 .17 1.90 -.25 1.37 1.68 1.08 4.17 2.38 3.28 3.52 3.95 4.52 3.90 6.16 4.63 8.01 6.36 9.15 7.76 7.22 8.79 $-.71 4.62 7.58 -1.50 2.50 6.85 4.01 15.58 7.32 11.45 6.91 13.31 13.58 14.68 13.61 13.80 20.67 16.56 21.30 18.93 15.54 20.57 16.79 18.89 22.26 21.35 23.57 19.85 21.37 $-.50 3.23 5.31 -1.05 1.75 4.80 2.81 10.91 5.12 8.01 4.84 9.32 9.51 10.28 9.53 9.66 14.47 11.59 14.91 13.25 10.88 14.40 11.75 13.22 15.58 14.95 16.50 13.90 14.96 $-.29 1.85 3.03 -.60 1.00 2.74 1.60 6.23 2.93 4.58 2.77 5.32 5.43 5.88 5.44 5.51 8.27 6.62 8.52 7.57 6.21 8.23 6.71 7.56 8.90 8.53 9.43 7.94 8.55 Aledo II. Dark soils with noncalcare- ous subsoils III. Brownish-yellow soils with open, noncalcareous subsoils IV. Dark soils with open, non- calcareous subsoils V. Dark soils with impervious, calcareous subsoils joliet VI. Dark soils with impervious, noncalcareous subsoils Carthage Average VII. Sandy loams and sands Oquawka VIII. Yellow soils with noncal- careous subsoils Enfield Average IX. Gray soils with impervious, noncalcareous subsoils Toledo Odin Raleigh 21.77 20.81 28.85 26.62 23.01 22.24 15.24 14.57 20.19 18.63 16.11 15.57 8.71 8.32 11.54 10.65 9.20 8.90 Sparta Newton X. Hilly land Elizabethtown . . 1 See page 346. 1934} RESPONSE OF ILLINOIS SOILS TO LIMESTONE 351 the fields. At the higher prices there is a margin on practically all fields. The ton-values of the limestone used on these fields at the medium prices for the crop increases are shown graphically in Fig. 26. These values vary more consistently with the natural level of soil produc- tivity than do the acre-values shown in Fig. 25. The spread between the various soil groups in the ton-values of the limestone applied is 12 Y 3ZI SOIL GROUPS FIG. 26. TON- VALUES OF LIMESTONE AS MEASURED BY CROP INCREASES The value of limestone in these experiments tended to vary more con- sistently with the natural productivity level of the soil than did the acre-values (Fig. 25). The less productive soils have given large returns for each ton of limestone used. (Based on medium crop prices.) also somewhat greater than the spread between the acre-values. The relative differences between the ton-values in the manure system and those in the residues system are similar to the differences shown for the acre-values in the two systems. The striking fact about these re- sults is that each ton of limestone has, as an average, produced crop increases worth more than the cost of the limestone ; and that on the less productive light-colored soils the net returns per ton of limestone have been four to five times as great as the investment made. Problems of Economic Worth The economic advantages accruing from the use of limestone, or any other fertilizer material for that matter, may be considered from three points of view ; namely, 352 BULLETIN No. 405 [June, 1. The crop point of view; that is, the effect of lime in increas- ing crop yields. 2. The fertilizer point of view ; that is, the margin remaining after the costs of using the limestone have been deducted from the value of the increased yields. 3. The farm point of view; that is, whether, even with increases from the use of limestone, a margin of profit for the farm as a whole remains after all farming expenses have been cared for. The effectiveness of limestone in increasing crop yields has been amply demonstrated on many Illinois soils. The money returns from increased yields resulting from the use of limestone have, on many soils, been large enough to cover all the costs involved in making the limestone applications and leave margins of varying size. The fact that a fertilizer may produce large increases in yields or striking money returns per ton of limestone or per acre of crops does not necessarily mean, however, that it can make farming profitable on some soils. The yields without limestone may be so low that any possible increases that might result from the use of limestone would not bring the yields up to a point that would enable a farmer to pay all the expenses of his farm and realize a satisfactory margin of profit. On the Sparta and Odin fields, for example, increases from limestone were excellent, yet the total yields were so small that at ordinary price-levels the total income from such land would not cover even the bare expenses of farming. On the Mt. Morris field, on the other hand, where yields without limestone are high enough to make farming profitable under normal price conditions, increases that were small compared with the Sparta and Odin increases would still be large enough to contribute measurably to further profits. Thus sizable increases from fertilizers may lead one to false con- clusions about their practical value unless note is taken of the basic yields of the soil without fertilizer treatment. RELATION OF LIMESTONE TO VARIOUS SOIL PRODUCTIVITY FACTORS The implications involved in such proverbial phrases as "a lime- stone country is a rich country," led early investigators to believe that limestone could be applied to any soil in any amount without adverse influences except in the matter of unnecessary expense. Such ideas prevailed at the time many of the Illinois soil experiment fields were established. Consequently the plans developed for the use of lime- 1934] RESPONSE OF ILLINOIS SOILS TO LIMESTONE 353 stone on these fields provided for its rather liberal use, as described on page 305, in order to make sure that enough would be applied to replace the losses that occur as a natural consequence of cropping and leaching. With the passing years questions began to arise about whether so much limestone was necessary. If limestone was not lost so rapidly from the soil as had been supposed, then smaller applications or a less frequent use of it would be even more profitable than the larger amounts called for in the early experiments. The advisability of ap- plying limestone at uniform and regular rates on all kinds of soils also began to be questioned. Limestone was not producing profitable increases on some of the experiment fields, probably because it was not needed. Then there arose the question whether excessive quantities of limestone might not have a retarding influence on various soil processes related to crop production. These questions can be con- sidered in the light of existing experiment-field results. Still others can be answered only by further investigation in the field and in the laboratory. A brief discussion of some of these problems is of interest at this point. Soil Acidity One of the important functions of limestone is to correct certain conditions that hinder the growth of some legume crops. The most important of these conditions is known as soil acidity. It is well known that soil acidity varies greatly among soil types and to some extent within the same soil type (see Table 2). Because of this fact it is likely to vary more or less among fields on the same farm and even in different parts of the same field. Thus such legumes as sweet clover, alfalfa, red clover, etc., may grow well on some soil types, or on some fields, or in some parts of a particular field, and grow indifferently or not at all in other places, according to the acidity of the soil. Since in residues systems of farming the proper utilization of the legume crop has marked effect upon the general crop-producing power of the soil, the farmer's chief interest should be to so maintain the fertility of his soil that legumes will grow abundantly. And since the ability of soils to grow the various legumes successfully is more or less directly related to the degree, or intensity, of soil acidity, the best plan is to use limestone in direct proportion to the intensity of the acidity of the soil. In other words, limestone should be applied only when it is needed to encourage the growth of leguminous crops. Such a practice would often do away with regular applications. 354 BULLETIN No. 405 [June, On many of the experiment fields the initial application of lime- stone is proving effective for longer periods than was anticipated when the fields were established. The results from the West Salem field, described on page 343, for example, are especially significant. Phosphorus Availability The opinion is now widely held that a too liberal use of limestone may interfere with the availability of phosphates and especially of applied rock phosphate. Theoretical reasoning provides justification for the above opinion. There are several forms of calcium phosphates which vary consider- ably in solubility and hence in availability. Rock phosphate has most of its phosphorus in the form of tricalcium phosphate, which is rela- tively insoluble in water. When acted upon by acids it loses some of its calcium, which is converted into the calcium salts of those acids. When one-third of the calcium is removed, the phosphate becomes dicalcium phosphate, and when two-thirds are removed it becomes monocalcium phosphate. The more calcium the phosphate loses, the more soluble it becomes and the more available for plant use. How- ever, unless conditions exist that will dispose of the calcium that is lost from the phosphate, it may reunite with the phosphate and again render the phosphate less available. The growing of such crops as alfalfa, red clover, sweet clover, and others that have high calcium requirements provides one way in which to utilize this calcium. Good drainage may also be helpful in re- moving it. Soil acids, by uniting with the calcium, are another means of preventing calcium from reuniting with the phosphate. Some soil acidity is likely, therefore, to be of value in rendering phosphates available, especially the phosphates of rock phosphate. If, on the other hand, limestone, which is also a calcium compound, is applied too liberally it may tend to satisfy the calcium requirements of both the high-calcium crops grown and the acids in the soil and in this way prevent the removal of calcium from the phosphate and reduce the effectiveness of the phosphate. The above reasoning is supported by experiments in the green- house and in the laboratory. It is supported also by field investigations in many states, including experiments started on the Aledo field in Mercer county, Illinois, in 1916. Four carriers of phosphorus have been applied to plots on the Aledo field with and without limestone. Where used, the limestone was applied at the rate of 6 tons an acre. The values of the crop increases 1934] RESPONSE OF ILLINOIS SOILS TO LIMESTONE 355 for the phosphates during the last rotation period (1929-1932) are recorded in Table 12. Without exception the phosphates were less effective when applied with limestone than when used alone. This would seem to indicate that limestone reduces the effectiveness of phosphates and that in practice limestone should not be applied with phosphates or at least should be applied only sparingly. TABLE 12. AVERAGE ANNUAL ACRE-VALUES OF CROP INCREASES FROM PHOSPHATES USED WITH AND WITHOUT LIMESTONE (Aledo field, 1929-1932) Phosphorus carrier Without limestone With limestone Decrease for limestone Bone phosphate $7.31 $2.94 $4.37 Superphosphate 6.28 2.37 3.91 Rock phosphate 6.24 1.46 4.78 Slag phosphate 6.51 1.60 4.91 Whether such a conclusion is entirely sound depends upon other considerations. Since both the limestone and the phosphates carried calcium, it is possible that at least part or even all of the effects of the phosphates were in reality due to the calcium, which has a high value on acid soils. It is of interest, therefore, to compare the total com- bined increases resulting from the limestone and the phosphates when used separately with the increases from these two fertilizing materi- als when applied together. If the increases from the associated ap- plications were equal to the total combined increases from the sepa- rate applications, then it would be clear that limestone and phosphates were exerting independent action on crop yields. If the increases from the associated applications were smaller than the total com- bined increases from the two separate treatments, then it would ap- pear that these two materials do have some overlapping effects and that one may be substituted for the other to the extent of such over- lapping. As a matter of fact, the increases from limestone and phosphate applied together were considerably smaller than the total combined increases from the separate applications (Table 13), indicating that under these soil conditions these two materials do have, in part, a common function. The extent to which overlapping occurred sug- gests that phosphorus is a relatively unimportant fertilizer on this field, for when the overlapping values are subtracted from the values obtained with phosphate used alone, the increases are hardly sufficient to cover the cost of the phosphate. If calcium is the material most needed, it would appear that limestone alone would be the more 356 BULLETIN No. 405 [June, profitable investment. There is of course the possibility that smaller applications of limestone might have permitted larger responses from the phosphate, but the important question is whether such combi- nations would be as profitable. While the above conclusions seem applicable to the Aledo field and probably to other kinds of soils also, this does not mean that all soils would give similar results. Some soils may be so deficient in phos- phorus as to respond satisfactorily to phosphate fertilizers even when TABLE 13. AVERAGE ANNUAL ACRE-VALUES OF CROP INCREASES FROM LIMESTONE AND PHOSPHATES USED SEPARATELY AND USED IN COMBINATION (Aledo field, 1929-1932) Series Carrier of phosphorus Increases from limestone and phosphate used separately Increases from associ- ated applica- tions Over- lapping effects 1 Limestone alone Phosphate alone Combined increases 500 (1) $6.22 7.33 8.73 8.10 (2) $7.31 6.28 6.24 6.51 (3) $13.53 13.61 14.97 14.61 (4) $9.16 9.70 9.99 9.70 (5) $4.37 3.91 4.78 4.91 Slag phosphate .... 'Calculated as the difference between the combined effects when used separately (Column 3) and the increases from associated applications (Column 4). applied with limestone. The Bloomington field, located in McLean county on a semimature, dark-colored soil that has a heavy, noncalcare- ous subsoil, has exhibited such a response. On this field rock phos- phate used in addition to limestone has given increases in crop yields worth $10.15 an acre annually as an average during the last five years. Superphosphate and bone phosphate applied with limestone have given values of $7.54 and $11.94 respectively. Somewhat similar results have been obtained on other fields. On very acid soils lime applica- tions have long been recognized as essential for best results from phosphates. In these soils the iron and aluminum compounds tend to convert the phosphorus into rather insoluble forms, while limestone tends to keep it in forms more readily available for crop use. Thus it would appear that type of soil is an important factor in the interaction between limestone and phosphate ; and that while some soil acidity may increase the effectiveness of rock phosphate, too in- tensive acidity may have' the opposite effect. So far as phosphorus availability is concerned, therefore, care should be taken to avoid both overliming and underliming. Until these matters are better understood, limestone applications should be made as indicated by a 1934^ RESPONSE OF ILLINOIS SOILS TO LIMESTONE 357 systematic soil-testing program such as is outlined in Circular 346 of this Station, "Test Your Soil for Acidity." The interaction between limestone and phosphate in the soil, just discussed, raises another question. If strongly acid soils tend to change phosphorus to the more insoluble iron and aluminum forms, and thus perhaps cause a deficiency of phosphorus for crop production, would the application of limestone without accompanying phosphate appli- cations tend to reduce the phosphorus deficiency? If so, would such reduction remove the necessity for applying phosphates, or at least delay the need for them? Some preliminary studies, especially those with deep-rooting le- gumes, indicate that the availability of phosphorus has been greatly increased in some soils so treated and unaffected in others. The prob- lem presents complications that need thoro study before final con- clusions can be drawn. It is quite possible, however, that the effect- iveness of limestone in making available the supplies of phosphorus naturally in the soil may be a better explanation for the poor crop response to applied phosphate on some soils than an explanation based on the overliming idea. Potash Availability Potassium is another plant- food element whose availability may be interfered with by the use of limestone. This is suggested by the results from certain experiments with potash fertilizers and limestone on silt loam soils, practically all of which contain naturally rather large amounts of potassium. Corn yields on the Ewing field, for example, a silt loam, have shown little variation on unlimed land (R) over a period of twenty-three years (Fig. 27). Yields on limed land (RL and RLP) have declined at the rate of three-quarters of a bushel to nearly a bushel annually. Yields on plots given the same treatments as those just mentioned, except for the addition of potas- sium (RLPK), have increased by more than half a bushel of corn an acre a year, changing from 37.6 bushels in 1910 to 49.3 bushels in 1932. Experience with alkali soils further strengthens the suggestion that limestone may be involved in the development of a potash de- ficiency from the standpoint of crop production. It has long been known that alkali soils, which are characterized by high carbonate content, respond markedly to potassium fertilizers even tho the natural content of the soil may be fairly high. The alkali appears to reduce the solubility and availability of the soil potassium. Since the amount of limestone applied in the Ewing experiments and others was some- 358 BULLETIN No. 405 [June, what liberal, the effects may be somewhat similar to those in soils where natural alkali conditions exist. Experiments in Tennessee and elsewhere, showing that the amount of potassium leached from soils can be reduced by applying various kinds of limestone, add further weight to the suggestion that the application of limestone to the Ewing field may have reduced the availability of the soil potassium. 50 40 ffl 30 20 10 -RLP 1910 1922 1934 FIG. 27. EFFECT OF POTASH AND LIMESTONE ON CORN YIELDS ON EWING EXPERIMENT FIELD On some of the more mature soils the use of limestone appears to lead to a potash deficiency. On the unlimed soil of the Ewing field the corn yields showed a moderate downward trend over a twenty-two year period, but where limestone was applied in addition to crop residues, a much more marked decline occurred. The use of potash fertilizers has resulted in steadily improving yields. (Trends calculated from annual yields by using formula y = n + mx.) Another explanation for the increasing deficiency of available potassium that has accompanied applications of limestone is that lime- stone, by encouraging larger crops thru the growth of legumes, has caused a greater draft on the natural supplies of available potassium. When these fields were first established, the limestone applied helped materially in growing larger crops. The larger crops naturally took larger amounts of potassium from the soil. As time went on, the amounts of available potassium were depleted faster than the unavail- able forms could be converted into forms for crop use, and the plants encountered more and more difficulty in getting the potassium they needed for normal growth. Under such circumstances the applica- 1934~\ RESPONSE OF ILLINOIS SOILS TO LIMESTONE 359 tion of potassium in available form would be expected to have grad- ually increasing effects on crop yields. In the Illinois experiments sweet clover, which was always grown on the plots receiving limestone, was usually plowed under the fol- lowing spring as a green manure for corn. The benefits from applied potash have seemed to increase when the sweet clover was handled in this way, even tho sweet clover itself contains a good percentage of potassium. Some investigators have suggested, in explanation of these results, that a biological factor involving the excessive produc- tion of nitrate nitrogen might be responsible for the declining crop yields on limestone-sweet-clover plots to which no potash was applied. Their explanation is that the limestone-sweet-clover combination pro- vides especially favorable conditions for the excessive production of nitrate nitrogen, and that in the absence of sufficient available potas- sium, large accumulations of nitrate nitrogen may have a detrimental effect on crop growth, especially on a crop like corn. Under such con- ditions the application of potash fertilizers would have marked bene- ficial effects. Whatever the cause may be for the available potassium deficiency under the limestone-sweet-clover system of soil management, it seems safe to conclude that the system has unquestioned merit for large areas of Illinois soils even tho on some soils applications of potash are needed for the best results. INCREASING USE OF AGRICULTURAL LIMESTONE The important place that limestone occupies in the management of Illinois soils is clearly demonstrated by the analyses presented in the foregoing pages. The dissemination of facts concerning liming experiments as they have become available, and later the encourage- ment given soil-testing and mapping by extension agencies, have brought about a widespread use of limestone by Illinois farmers. The first authentic record of the amount of limestone applied to Illinois soils covers the year 1906 and shows a total of 2,000 tons. Continuous and rapid increases took place each year until a peak of 925,000 tons was reached in 1929. This amount, according to statistics published by the National Lime Association, was about one- fourth the total amount of lime materials used for agricultural purposes in the United States that year. Even tho large tonnages of agricultural limestone have been used 360 BULLETIN No. 405 [June, in Illinois, there are still many lime-deficient fields that have never had limestone applied to them. Some of these fields are located on marginal land to which the application of limestone would probably not be economically justified even under more normal times. There are many other fields, however, on which limestone will prove profit- able when economic conditions are more normal. There are other soils in the state possessing high levels of productivity that are be- ginning to show lime deficiencies which will be intensified under con- tinued cultivation unless limestone is applied. Lime renewals will always need the attention of Illinois farmers, and limestone must remain the key to any successful soil-building program on the lime-deficient soils of the state. 1 SUMMARY AND CONCLUSIONS Limestone has long been recognized as of fundamental importance in Illinois agriculture. For the past twenty-five years its use steadily increased until the present depression period. This bulletin analyzes the response of various soils and crops to limestone on forty experi- ment fields located thruout the state on various kinds of soil, some of the fields having been in operation for thirty years. The principal facts brought out by the study are the following: 1. The degree of response made by Illinois soils to limestone, as measured by crop increases, is closely related to the natural produc- tivity of the soil. Soils of high natural productivity respond least and those of low natural productivity most. The range in response for the different kinds of soils, as measured by yields of all crops grown, varied from nothing to more than 150 percent. 2. The degree of response to limestone bears a close relationship to certain chemical characters of the soil, one of which is the degree of saturation with replaceable calcium and magnesium as compared with the total base-exchange capacity of the soil. Soils with a low percentage saturation respond best to limestone. Soils exhibiting about 80 percent saturation give little or no response. Comparison of the various chemical characters of a soil with its response to limestone indicates the value of proper chemical tests for quickly determining the lime requirements. 3. Different crops respond differently to limestone applications. On the dark-colored soils the response of the corn, oats, wheat, and 'See Circular 375 of this Station, "Limestone the Key to Soil Building and Higher Crop Yields," for further discussion of this subject. 1934] RESPONSE OF ILLINOIS SOILS TO LIMESTONE 361 hay crops \vas somewhat similar, tho oats tended to be the least re- sponsive. On the light-colored soils wheat made a much better re- sponse than corn, tho all crops, especially hay, made large responses. On sandy soil the differences between the corn and wheat responses were not great ; and both crops showed better responses on this soil than on the dark-colored soils. On the sandy soil the application of limestone made the difference between good hay yields and no yields at all. 4. The use of limestone on the light-colored soils has tended to raise the productive levels of such soils to about 50 percent of the levels of the better untreated dark-colored soils. The combined in- fluence of organic manures and limestone has raised the light-colored soils to levels approximately 60 percent as high as the better untreated dark-colored soils. 5. Soils that have shown a high response to limestone applications have tended to show that response quickly. Soils that have shown only a moderate response have tended to be somewhat slow in evi- dencing that response, tho they usually have shown considerable ac- celeration in response after the first or second rotation. Some highly productive soils have shown no response until recent years, indicating that there has been a slow development of lime deficiency. Some soils, after exhibiting considerable acceleration in their response for a num- ber of years, have then shown a leveling out of response and then a falling off. Such behavior is probably due to increasing deficiencies in the supplies of other plant nutrients. On many soils increases from limestone have continued for some years after applications have been discontinued, showing the cumulative effect of proper applica- tions of limestone. 6. Increasingly larger crop yields for eight years were obtained from a single 4-ton application of limestone on a lime-deficient light- colored soil. After eight years there was a leveling out of the re- sponse and then a decline. After twenty years, however, the single application still showed some effect on crop yields. Repeated applica- tions during this twenty-year period proved no more effective than the single application until after the eighth year, when greater crop in- creases were shown for them than for the single application. 7. Limestone should be applied in amounts meeting rather closely the actual crop requirements. Smaller amounts may be altogether without effect. Larger amounts will be not only uneconomical but they may tend to reduce the availability of other plant nutrients, such as phosphorus and potassium. These facts indicate the value of definite 362 BULLETIN No. 405 [June, tests by which the lime deficiency of given fields or parts of fields may be quickly and accurately judged. 8. The thirty years of experimental evidence summarized here in- dicates that lime materials are a. Indispensable for successful crop production on many soils. b. Highly desirable for efficient production on other soils. c . Without much actual or economic effect on other soils. There is also evidence showing that nonresponsive soils may, with continued cultivation, become sufficiently lime-deficient to respond to limestone applications ; and that the chemical, physical, and biological changes produced by the application of lime materials may in time create new soil conditions that have to be recognized in management practices. 1934~\ RESPONSE OF ILLINOIS SOILS TO LIMESTONE 363 For the practical application of the facts dis- cussed in this bulletin, see Circular 346, "Test Your Soil for Acidity" Circular 375, "Limestone the Key to Soil Building and Higher Crop Yields" UNIVERSITY OF ILLINOIS-URBANA