LIBRARY OF THE 
 
 UNIVERSITY OF ILLINOIS 
 
 AT URBANA-CHAMPAICN 
 
 630.7 
 
MOM CIRCULATING 
 
 CHECK FOR UNBOUND 
 CIRCULATING COPY 
 
UNIVERSITY OF ILLINOIS 
 
 Agricultural Experiment Station 
 
 BULLETIN No. 258 
 
 EXPERIMENTS WITH SUBSOILING, 
 DEEP TILLING, AND SUBSOIL 
 DYNAMITING ; 
 
 BY RAYMOND S. SMITH 
 
 THE UBRARY OF THE 
 
 MAR 28 1925 
 
 UNIVEKSIIY vt ILLINOIS 
 
 URBANA, IT.TJNOIS, FEBRUARY, 1925 
 
SUMMARY 
 
 Deep plowing and subsoil dynamiting experiments in 
 Illinois as well as in other states indicate that these tillage 
 methods cannot be expected materially to increase crop yields. 
 That such methods are not superior to ordinary or medium- 
 depth plowing has been indicated by subsoiling experiments 
 conducted by the Illinois Agricultural Experiment Station on 
 Gray Silt Loam On Tight Clay at Odin, Marion county; 
 subsoiling, deep tilling, and dynamiting experiments on Gray 
 Silt Loam On Tight Clay at Toledo, Cumberland county; 
 and deep tilling experiments on Brown Silt Loam at Urbana, 
 Champaign county. 
 
 Soil moisture determinations made during two seasons 
 on the variously tilled plots at Toledo show that none of the 
 tillage treatments used increased the downward movement 
 of moisture thru the soil. 
 
EXPERIMENTS WITH SUBSOILING, DEEP 
 TILLING, AND SUBSOIL DYNAMITING 
 
 By RAYMOND S. SMITH, Associate Chief in Soil Physics 
 
 Good plowing is often taken to mean deep plowing. The two, how- 
 ever, are not associated, and before a farmer decides to increase the 
 depth of plowing beyond about 7 inches, he should consider whether the 
 probable benefits will more than pay for the increased cost. 
 
 The purpose of plowing is to turn under organic matter of various 
 kinds, to pulverize the surface so that the seed may be covered at the 
 right depth, to control weeds, and to check surface runoff. In heavy 
 soils, or soils which pack badly after rains, plowing is effective in help- 
 ing to maintain a favorable physical condition. Plowing does not increase 
 the water-holding capacity of the soil, even in arid regions; it does, 
 however, increase the power of the soil to absorb rainfall, thus decreas- 
 ing the amount of water carried away by surface runoff. 
 
 The supposed desirability of deep plowing seems to be based on the 
 belief that only the portion of the soil which is loosened by the plow is 
 utilized by the roots of the crop. There are no reasons for believing 
 that the roots of crop plants behave in any way essentially different 
 from the roots of wild plants, and the luxuriant growth of wild vegeta- 
 tion on land which has never been plowed is a matter of common 
 knowledge. 
 
 There are soils, however, which are unfavorable to root penetration 
 because they have an impervious subsoil, and it would be very desirable 
 to overcome this condition. Whether this can be done by deep tillage 
 of any kind will be discussed later. 
 
 The increased cost of deep plowing is considerable. If the depth 
 is increased one inch, about 300,000 pounds, or 150 tons, of additional 
 soil is turned for every acre plowed. This additional weight cannot be 
 moved without expenditure of additional power, and power on the 
 farm is costly. 
 
 In this bulletin the terms shallow, medium, and deep plowing are 
 used with the following meanings: 
 
 Shallow plowing, less than 5 inches deep 
 Medium plowing, between 5 and 8 inches 
 Deep plowing, more than 8 inches deep 
 
 The only way to determine, with any degree of accuracy, how deep 
 the plow is running is to make several careful measurements. It is almost 
 
 155 
 
156 
 
 BULLETIN No. 258 
 
 [February, 
 
 always true that the plowman thinks he is plowing deeper than he 
 actually is. 
 
 The subject of depth of plowing is of such general interest that a 
 few of the experiments which have been conducted in other states, and 
 all the Illinois experiments will be presented in this bulletin so that the 
 reader may see whether there is any basis for the expectation that deep 
 plowing will increase yields. 
 
 PLOWING EXPERIMENTS IN OTHER STATES 
 
 In 1918 Chilcott and Cole, 1 of the Bureau of Plant Industry of the 
 United States Department of Agriculture, reported the results of exten- 
 sive deep tillage work in the Great Plains which had been carried on 
 for a period of years at twelve stations in nine states. The authors con- 
 cluded that the "average results of a series of years show no measurable 
 effect on crop yields as a result of subsoiling." 
 
 Results obtained by the Ohio Agricultural Experiment Station 
 from experiments comparing ordinary plowing, deep plowing, and sub- 
 soiling, are summarized in Table 1. The authors comment on these 
 results as follows : "It would be difficult to arrange a uniform treatment 
 which would result in yields more nearly identical. In view of the ex- 
 pense involved, it is evident that the 7-inch plowing is by far the most 
 profitable." 
 
 TABLE 1. AVERAGE YIELDS PER ACRE FOR TWELVE YEARS FOLLOWING DIFFERENT 
 
 DEPTHS OF PLOWING 
 
 (From Ohio Agricultural Experiment Station Bulletin 362) 
 
 Crop 
 
 Ordinary plowing 
 (7# inches) 
 
 Deep plowing 
 (15 inches) 
 
 Ordinary plowing 
 plus subsoiling 
 
 Grain 
 
 Straw or 
 hay 
 
 Grain 
 
 Straw or 
 hay 
 
 Grain 
 
 Straw or 
 hay 
 
 Corn 
 
 bu. 
 61.13 
 49.00 
 31.50 
 
 Ibs. 
 3 251 
 2 159 
 3 483 
 5 300 
 
 bu. 
 59.47 
 49.29 
 31.49 
 
 Ibs. 
 3 066 
 2 048 
 3 517 
 5 060 
 
 bu. 
 61.33 
 49.05 
 31.65 
 
 Ibs. 
 3 229 
 2 188 
 3 549 
 5 200 
 
 Oats 
 
 Wheat 
 
 Clover 
 
 Noll, 1 of the Pennsylvania Agricultural Experiment Station, reports 
 several years' work comparing the effect of ordinary plowing (7 inches) 
 and deep plowing (12 inches), on the yields of corn, oats, barley, wheat, 
 and alfalfa. He was led to conclude that "the two kinds of plowing gave 
 practically the same results on all crops grown." Since the results with 
 alfalfa are of special interest, they are given in Table 2. 
 
 Chilcott, E. C., and Cole, John S. Subsoiling, deep tilling, and soil dynamiting in 
 the Great Plains. Jour. Agr. Res. 14:481-521, 1918. 
 
.7925] SUBSOILING, DEEP TILLING, AND DYNAMITING 157 
 
 Numerous other experiments on depth of plowing, conducted under 
 a wide range of climatic and soil conditions in many states, all lead to 
 the conclusion that, while occasionally a combination of soil and climatic 
 
 TABLE 2. YIELD OF ALFALFA FROM SHALLOW AND FROM DEEP-PLOWED PLOTS* 
 (From Pennsylvania Agricultural Experiment Station Annual Report, 1912-1913) 
 
 
 Shallow-plowed 
 plots 
 
 Deep-plowed 
 plots 
 
 First cutting 
 
 Ibs. 
 1 768 
 
 Ibs. 
 1 725 
 
 Third cutting 
 
 871 
 
 827 
 
 *Second cutting not harvested because it was too light owing to drouth. 
 
 conditions may occur which makes deep plowing profitable, the returns 
 thru a period of years will not justify the increased cost, excepting pos- 
 sibly in the case of sugar beets. 
 
 SUBSOIL DYNAMITING EXPERIMENTS IN 
 OTHER STATES 
 
 The use of dynamite on soils having an impervious subsoil is 
 strongly recommended by concerns having this material for sale. The 
 fact that the character of the impervious material determines whether 
 or not dynamite can be used beneficially seems to have been overlooked 
 by them in their advertising. The effect of the exploding charge on a 
 plastic clay subsoil is injurious rather than beneficial because the clay 
 is compacted and not shattered. The accompanying illustration from 
 Bulletin 209 of the Kansas Agricultural Experiment Station (Fig. 1) 
 shows the effect produced by exploding a charge of dynamite in such a 
 subsoil. The soil particles are forced out from the center of the charge 
 and into the pore spaces of the surrounding soil mass, forming dense 
 walls. These walls are very strongly compacted and may be easily sep- 
 arated from the adjacent soil, as was done in this Kansas work. Pro- 
 fessors Call and Throckmorton comment as follows on the effect of 
 dynamiting plastic clay subsoils: "It is evident from these observations 
 that dynamiting does not crack and loosen plastic clay subsoils. In 
 fact, the opposite effect is produced. The soil, instead of being shattered 
 and cracked, is compacted and puddled, and the soil left in poorer physi- 
 cal condition than before the dynamiting was done." Similar effects 
 were noted in the dynamiting experiments at Toledo, Illinois, which are 
 discussed beginning on page r&l. A number of other states have 
 conducted subsoil dynamiting experiments and the results of practically 
 
 C. F. Pennsylvania Agricultural Experiment Station Annual Report, 1912- 
 1913. 
 
158 BULLETIN No. 258 [February, 
 
 FIG. 1. A PARTLY BROKEN DYNAMITE JUG IN A HEAVY PLASTIC SUBSOIL 
 
 Produced by one-half stick of 20-percent "Red Cross" powder placed in the 
 soil at a depth of three feet. Cavity twelve inches wide and fifteen inches deep; 
 thickness of walls varied from two to six inches. "The soil, instead of being shat- 
 tered and cracked, is compacted and puddled, and left in poorer physical condition 
 than before the dynamiting was done." (Courtesy of the Kansas Agricultural 
 Experiment Station.) 
 
 all of these experiments lead to the conclusion that for general farm 
 crops as well as for fruit trees, the effect of dynamiting plastic subsoils 
 is injurious rather than beneficial. 
 
 PLOWING EXPERIMENTS IN ILLINOIS 
 
 Considerable work has been done in Illinois in comparing the 
 effects of medium and deep plowing, as already defined, on crop yields. 
 The following experiments, all of which have been discontinued, include 
 all the plowing studies made by this Station, excepting some early work 
 with sugar beets, the results of which were published in 1898 in Bul- 
 letin 49. 
 
 EXPERIMENT AT ODIN : GRAY SILT LOAM ON TIG'HT CLAY 
 
 From 1907 to 1919 a subsoiling experiment was carried on at the 
 Odin experiment field, in Marion county. The soil on this field is classi- 
 fied as Gray Silt Loam On Tight Clay. The plastic, difficultly pervious 
 stratum known as "tight clay" is from 8 to 12 inches thick and generally 
 occurs about 19 inches below the surface, tho there is a great variation 
 in its depth. In some places it comes very close to the surface, and gives 
 rise to what are known as "scald spots." 
 
SUBSOILING, DEEP TILLING, AND DYNAMITING 
 
 159 
 
 TABLE 3. ACRE YIELDS OF CORN GROWN ON GRAY SILT LOAM ON TIGHT CLAY, NOT 
 TILE-DRAINED: ODIN FIELD 
 
 Plot 
 
 1 
 
 2 
 
 3 
 
 4 
 
 5 
 
 
 Soil treatment 1 
 
 None 
 
 R 
 
 RL 
 
 RLP 
 
 RLPK 
 
 Tillage 
 treatment . . 
 
 Not 
 sub- 
 soiled 
 
 Sub- 
 soiled 
 
 Not 
 sub- 
 soiled 
 
 Sub- 
 soiled 
 
 Not 
 sub- 
 soiled 
 
 Sub- 
 soiled 
 
 Not 
 sub- 
 soiled 
 
 Sub- 
 soiled 
 
 Not 
 sub- 
 soiled 
 
 Sub- 
 soiled 
 
 1907 2 ... 
 
 bu. 
 50.3 
 42.2 
 28.6 
 32.8 
 22.8 
 28.2 
 -3.8 
 5.2 
 48.6 
 17.6 
 7.4 
 2.8 
 0.8 
 
 bu. 
 
 7.3 
 36.4 
 27.2 
 17.9 
 19.6 
 32.2 
 3.6 
 2.8 
 38.8 
 14.0 
 9.4 
 6.0 
 0.3 
 
 bu. 
 
 49.9 
 37.8 
 32.8 
 26.5 
 22.6 
 40.8 
 6.0 
 2.0 
 46.0 
 16.2 
 12.7 
 6.8 
 1.2 
 
 bu. 
 38.9 
 24.8 
 29.8 
 31.4 
 24.4 
 
 bu. 
 41.8 
 34.6 
 27.8 
 38.0 
 21.6 
 
 bu. 
 48.8 
 31.4 
 26.8 
 37.8 
 23^0- 
 A4.2 
 11.2 
 1.8 
 46.4 
 23.4 
 8.0 
 9.0 
 4.1 
 
 bu. 
 48.6 
 40.4 
 36.2 
 36.6 
 21.8 
 41.2 
 5.0 
 2.0 
 44.8 
 20.6 
 7.0 
 10.4 
 2.2 
 
 bu. 
 
 42.8 
 45.8 
 34.2 
 36.5 
 20.6 
 52.0 
 3.6 
 2.8 
 42.0 
 22.2 
 12.0 
 9.6 
 2.1 
 
 bu. 
 
 70.8 
 75.0 
 71.8 
 76.7 
 39.2 
 68.8 
 11.6 
 2.8 
 61.2 
 28.0 
 34.6 
 17.2 
 2.8 
 
 bu. 
 63.5 
 
 57.8 
 66.4 
 85.4 
 47.6 
 57.2 
 11.8 
 5.2 
 55.2 
 23.4 
 32.8 
 18.2 
 1.9 
 
 1908 2 
 
 1909 . 
 
 1910 
 
 1911 
 
 1912 s ... . 
 
 14*3* 
 4.8 
 3.8 
 
 48.2 
 19.8 
 7.7 
 5.6 
 0.7 
 
 s P7z" 
 
 4.2 
 1.8 
 46.2 
 22.2 
 7.0 
 8.8 
 4.0 
 
 1913 2 
 
 1914 2 
 
 1915 2 
 
 1916 2 
 
 1917 
 
 1918 2 
 
 1919 
 
 
 Average . . 
 
 23.7 
 
 19.7 
 
 23.2 
 
 19.6 
 
 23.3 
 
 23.8 
 
 24.4 
 
 25.1 
 
 43.1 
 
 40.5 
 
 *R = residues, L = lime, P = rock phosphate, K = kainit. 
 
 2 Replowed in spring. 
 
 'Plowed and subsoiled in spring. 
 
 TABLE 4. ACRE YIELDS OF CORN GROWN ON GRAY SILT LOAM ON TIGHT CLAY, TILE- 
 DRAINED: ODIN FIELD 
 
 Plot 
 
 6 
 
 7 
 
 8 
 
 9 
 
 10 
 
 
 Soil treatment 
 
 None 
 
 R 
 
 RL 
 
 RLP 
 
 RLPK 
 
 Tillage 
 treatment . . 
 
 Not 
 sub- 
 soiled 
 
 Sub- 
 soiled 
 
 Not 
 sub- 
 soiled 
 
 Sub- 
 soiled 
 
 Not 
 sub- 
 soiled 
 
 Sub- 
 soiled 
 
 Not 
 sub- 
 soiled 
 
 Sub- 
 soiled 
 
 Not 
 sub- 
 soiled 
 
 Sub- 
 soiled 
 
 1907 1 
 
 bu. 
 38.5 
 28.8 
 30.0 
 24.9 
 10.8 
 24.0 
 1.2 
 3.4 
 22.0 
 9.2 
 11.1 
 5.6 
 0.1 
 
 bu. 
 27.9 
 28.6 
 21.0 
 27.2 
 7.0 
 31.2 
 2.8 
 5.2 
 24.6 
 10.8 
 9.7 
 6.0 
 0.3 
 
 bu. 
 50.3 
 28.6 
 28.0 
 39.1 
 15.4 
 38.4 
 1.8 
 4.6 
 35.0 
 15.2 
 15.4 
 8.0 
 0.2 
 
 bu. 
 47.4 
 28.0 
 24.6 
 38.8 
 15.4 
 33.2 
 2.4 
 4.8 
 38.4 
 13.2 
 12.8 
 7.0 
 0.2 
 
 bu. 
 52.8 
 36.4 
 30.6 
 42.6 
 27.8 
 53.0 
 4.0 
 2.4 
 49.0 
 16.8 
 15.4 
 14.2 
 1.6 
 
 **. 
 
 45.8 
 38.4 
 30.2 
 37.3 
 22.4 
 50.8 
 4.0 
 3.0 
 41.6 
 18.6 
 15.7 
 13.6 
 1.8 
 
 bu. 
 45.3 
 39.4 
 21.6 
 40.8 
 23.8 
 57.6 
 7.2 
 2.0 
 41.6 
 18.4 
 20.6 
 15.2 
 1.5 
 
 bu. 
 
 45.9 
 46.0 
 41.0 
 43.2 
 19.2 
 54.2 
 12.2 
 2.2 
 41.8 
 17.6 
 15.6 
 15.8 
 2.4 
 
 bu. 
 69.4 
 
 77.2 
 36.2 
 83.0 
 32.2 
 62.0 
 8.6 
 3.4 
 53.6 
 35.8 
 27.2 
 22.4 
 4.2 
 
 **. 
 
 55.3 
 62.8 
 54.4 
 85.9 
 33.2 
 39.8 
 8.6 
 4.8 
 44.8 
 30.6 
 27.6 
 21.2 
 4.6 
 
 1908 1 
 
 1909 
 
 1910 
 
 1911 
 
 1912 2 
 
 1913 1 
 
 1914 1 
 
 1915 1 
 
 1916 1 
 
 1917 
 
 1918 1 
 
 1919 
 
 
 Average 
 
 16.1 
 
 15.6 
 
 21.5 
 
 20.5 
 
 26.2 
 
 24.9 
 
 25.7 
 
 27.5 
 
 39.6 
 
 36.4 
 
 1 Replowed in spring. 
 
 "Plowed and subsoiled in spring. 
 
160 
 
 BULLETIN No. 258 
 
 [February, 
 
 TABLE 5. SUMMARY OF ACRE YIELDS OF CORN FROM TILED PLOTS AND FROM PLOTS 
 
 NOT TILED: ODIN FIELD 
 
 Soil treatment 
 
 None 
 
 R 
 
 RL 
 
 RLP 
 
 RLPK 
 
 Tillage 
 treatment . . 
 
 Not 
 sub- 
 soiled 
 
 Sub- 
 soiled 
 
 Not 
 sub- 
 soiled 
 
 Sub- 
 soiled 
 
 Not 
 sub- 
 soiled 
 
 Sub- 
 soiled 
 
 Not 
 sub- 
 soiled 
 
 Sub- 
 soiled 
 
 Not 
 sub- 
 soiled 
 
 Sub- 
 soiled 
 
 1907 1 
 
 bu. 
 44.4 
 35.5 
 29.3 
 28.9 
 16.8 
 26.1 
 2.5 
 4.3 
 35.3 
 13.4 
 9.3 
 4.2 
 0.5 
 
 bu. 
 37.6 
 32.5 
 24.1 
 22.5 
 13.3 
 31.7 
 3.2 
 4.0 
 31.7 
 12.4 
 9.5 
 6.0 
 0.3 
 
 bu. 
 50.1 
 33.2 
 30.4 
 32.8 
 19.0 
 39.6 
 3.9 
 3.3 
 40.5 
 15.7 
 14.1 
 7.4 
 0.7 
 
 bu. 
 43.2 
 26.4 
 27.2 
 35.1 
 19.9 
 24.0 
 3.6 
 4.3 
 43.3 
 16.5 
 10.3 
 6.3 
 0.4 
 
 bu. 
 
 47.3 
 35.5 
 29.2 
 40.3 
 24.7 
 48.6 
 4.1 
 2.1 
 47.6 
 19.5 
 11.2 
 11.5 
 2.8 
 
 bu. 
 
 47.3 
 34.9 
 28.5 
 37.5 
 22.7 
 47.5 
 4.1 
 2.4 
 44.0 
 21.0 
 11.8 
 11.3 
 3.0 
 
 bu. 
 47.0 
 39.9 
 28.9 
 38.7 
 22.8 
 49.4 
 6.1 
 2.0 
 43.2 
 19.5 
 13.8 
 12.8 
 1.9 
 
 bu. 
 44.4 
 45.9 
 37.6 
 39.9 
 19.9 
 53.1 
 7.9 
 2.5 
 41.9 
 19.9 
 13.8 
 12.7 
 2.3 
 
 bu. 
 70.1 
 76.1 
 54.0 
 79.9 
 35.7 
 65.4 
 10.1 
 3.1 
 57.4 
 31.9 
 30.9 
 19.8 
 3.5 
 
 bu. 
 59.4 
 60.3 
 60.4 
 85.7 
 40.4 
 48.5 
 10.2 
 5.0 
 50.0 
 27.0 
 30.2 
 19.7 
 3.3 
 
 1908 1 . . . 
 
 1909 
 
 1910 
 
 1911 
 
 1912 2 
 
 1913 1 
 
 1914 1 
 
 1915 1 
 
 1916 1 
 
 1917 
 
 1918 1 
 
 1919 
 
 
 Average . . 
 
 19.9 
 
 17.7 
 
 22.3 
 
 20.0 
 
 24.7 
 
 24.3 
 
 25.0 
 
 26.3 
 
 41.3 
 
 38.4 
 
 Treatment 
 
 None 
 
 Le 
 
 LeL 
 
 LeLP 
 
 LeLPK 
 
 Odin Summary of Corn Yields 
 
 Bushels per acre 
 
 5 10 IS 20 25 30 35 40 
 
 ^eplowed in spring. "Plowed and subsoiled in spring. 
 
 During this 13-year period the rotation used was corn, soybeans, 
 wheat, and clover. There were four failures of the corn crop, three poor 
 corn crops, four poor wheat crops, and twelve clover failures. The large 
 proportion of crop failures which occurred in spite of supposedly good 
 soil treatment makes it clear that crops on this soil type are very sensi- 
 tive to climatic conditions during the growing season. It was the appre- 
 ciation of this fact that led 
 to the starting of the sub- 
 soiling work, in an attempt 
 to determine whether such 
 tillage treatment would im- 
 prove the unfavorable sub- 
 soil condition. It should be 
 stated, however, that when 
 seasonal conditions are fa- 
 vorable, large crops can be 
 grown on this soil if it is 
 properly treated. 
 
 One-half of each plot was 
 plowed and subsoiled in the 
 late fall. Exceptions to this 
 procedure are noted in foot- 
 notes following Tables 3 
 and 4. The yields of the 
 crops other than corn are 
 omitted because they were 
 
 FIG. 2. SLIGHT VARIATIONS INDICATE THAT 
 SUBSOILING HAS No EFFECT ON CORN YIELDS 
 
1925~\ 
 
 SUBSOILING, DEEP TILLING, AND DYNAMITING 
 
 161 
 
 not harvested by half plots. The complete data for corn given in Tables 
 3 and 4 show the variations which enter into the averages given in the 
 summary, Table 5. 
 
 In every case the differences in yield between the subsoiled plots 
 and the plots not subsoiled are so small that the only possible conclusion 
 is that subsoiling has neither increased nor decreased the corn yields. 
 
 The averages given in Table 5 are shown in graphic form in Fig. 2. 
 
 EXPERIMENT AT TOLEDO: GRAY SILT LOAM ON TIGHT CLAY 
 
 In 1913 another experiment was started on Gray Silt Loam On 
 Tight Clay at Toledo, Cumberland county, to compare the effects of 
 subsoiling, deep tillage, and subsoil dynamiting with ordinary plowing, 
 in a rotation of corn, soybeans, wheat, and sweet clover. Four series of 
 four 1/10-acre plots each were laid out so that each crop was grown 
 each year. The second-year sweet clover stubble was plowed late in 
 
 FIG. 3. DEEP TILLAGE MACHINE. REAR DISK TURNS THE SOIL IN THE BOTTOM 
 OF FURROW MADE BY FRONT DISK 
 
 This machine mixed the subsurface and in places the subsoil with the surface soil 
 to such an extent as to change the color of the surface. Decreased yields were appar- 
 ently the result of this mixing. 
 
 the fall for corn. One ton of rock phosphate per acre was applied on all 
 plots in the fall of 1914, and again in the fall of 1918. Four tons of 
 limestone per acre was applied on all plots in 1913, three tons per acre 
 was applied for the 1917 crop, and two tons per acre for the 1921 crop. 
 The depth from the surface to the tight clay varies on this field, 
 as is always found to be the case with this soil type. In places, the 
 
162 
 
 BULLETIN No. 258 
 
 [February, 
 
 u 
 
 CN 
 
 h 
 
 U 
 
 __O o O vo O 
 
 *J ^ Or , QS 
 
 S ^o ^o ^o oo 
 
 g I s * OO Tfi OS 
 
 OS 
 
 u 
 
 cfl 
 
 jj- OS CS t^ to 
 
 o 
 
 OT 
 
 O OS vo i i OS 
 
 t 
 
 ^ T-l VO VO 00 
 
 rt co r^ oo oo 
 
 c * CN >or^ 
 
 u 
 
 Os 
 
 | S 
 
 n Os oc t-~ oo 
 jj, CN CN CN CN 
 
 
 C/) 
 
 O CN OS i CN 
 
 QJ W) Tf ^ Tt- 
 
 4-> OH ^ ^ 
 
 O 
 
 C ^ _ _ 
 
 C O OO O CM 
 
 U 
 
 > 10 10 o O 
 o co oo ^f vo 
 1 ' * co co vo 
 
 "^ OS O ^ CN 
 
 Os 
 
 o O O* 
 
 O 
 IO 
 
 
 
 S ^ vo 00 CN 
 Q CN (N CS CN 
 
 OS 
 
 c vc O VD -*< 
 
 (U 
 > O OO O 
 JD OS CN -0 CO 
 
 ^ co r^ o r- 
 
 CO 
 
 rt O covo tN 
 
 OS 
 
 O OS rf os vo 
 
 " . 
 
 _C vo OS vo OO 
 
 ^ vo oo r-^ vo 
 
 
 \J 
 
 <S) 
 
 ^ 
 
 o 
 tn 
 
 oo 
 
 <U 
 
 > o o o o 
 
 O oo vo O oo 
 "^j ' CN CN CN 
 
 4J 
 
 ns CN r^ o r^- 
 
 CO 
 
 co o VOCN 
 
 ^^ Oso 
 
 OS 
 
 
 ^ Tf co >o oo 
 
 n O OS ^ OS 
 
 >. *""' 
 
 
 to 
 
 o o o' os' oo 
 
 (J CO Tf CO -f 
 
 ^ 
 
 J vo CO O CN 
 
 CO 
 
 J3 oo oo co vo 
 
 ^ "^ ^" OO s ! 
 
 U 
 
 > oo oo 
 
 O OS CO * ' OS 
 
 OS 
 
 
 Ja oo oo os i i 
 
 1- " 
 
 QJ CS CN ^H ^H 
 
 ld^ d 
 
 VO 
 
 CO 
 
 ^VOTJHVO 
 
 ||| 
 
 * 2 <u 
 
 OS 
 
 J3 i i CO i i CN 
 
 O 
 
 w 
 
 O O r^ vo *-i 
 <? co CO -J' 
 
 Sol 
 
 ^Z i< 
 
 ^ *j CO 
 
 VO 
 
 g VO O OO OO 
 
 co CN vo OO CN 
 
 c 
 
 ^ vo vo CO O 
 
 ^ CO vo CN vo 
 
 OS 
 
 u3 
 
 ^3 .... 
 
 en O ^ Q 
 
 j^ t^ l^ OO OO 
 
 O 
 
 TfH 
 
 e^ CN Ot^ VO 
 
 ^w vo ^o r^ os 
 
 c vo ^~* r^ *~H 
 
 < vo oo vo Os 
 
 OS 
 
 g _ ^H rt rt 
 
 fL aj ^j d 
 
 _C CN --I -H O 
 
 /-) ^p \o vO vo 
 ^j co co CO co 
 
 rj CO CO CO co 
 
 CO 
 
 JH C^ OO *O OO 
 
 CO 
 
 ^ wi vo O vo 
 
 co T3 
 
 |_, ( _^ 
 
 OS 
 
 Q oo oo ON t^"- 
 
 u 
 
 _Q T-I CN CO CN 
 X 
 
 <s|! 
 
 l|l 
 
 O 
 O-i 
 
 
 is) v,o r^ oo 
 
 OS O CN 
 
 
 
 
 
 
 
 "3 
 
 rs 
 *>. 
 
 (U 
 
 
 
 
 8 Ci 
 I ^ 
 
 ex 
 
 IJ 
 glj 
 
 G^ 
 8Q 
 
.7925] SUBSOILING, DEEP TILLING, AND DYNAMITING 163 
 
 subsoil plow and deep tillage machine penetrated the tight clay, but as 
 a rule this impervious stratum occurred 1 to 16 inches below the depth 
 to which the implements ran. The deep tilling was done with a deep 
 tillage machine, illustrated in Fig. 3, which mixed the subsurface, and in 
 places the subsoil, with the surface soil to such an extent as to change 
 the color of the surface. On the dynamite plots, the charge was placed 
 well into the tight clay stratum. The size of the charge was determined 
 each year by experimentation, the object being to use as heavy a charge 
 as possible without blowing the soil out and forming a hole. The charges 
 usually consisted of one-third of a stick of 20-percent dynamite. They 
 were spaced 8 feet, 3 inches apart each way on two of the plots and 1 1 
 feet apart each way on the other two. Fig. 4 shows the method used 
 in spacing the charges. 
 
 The results of this experiment show that none of the tillage treat- 
 ments subsoiling, deep tilling, or dynamiting had any beneficial effect 
 on crop yields. Deep tilling apparently decreased yields, probably be- 
 cause of the mixing of the subsurface and subsoil with the surface soil. 
 
 Table 6 shows the yields of all the crops during the time of the 
 experiment, 1913 to 1922, and also the time when the various series 
 were plowed, subsoiled, deep-tilled, and dynamited. It should be ex- 
 plained that the tilling was done in the late fall of the year indicated, 
 for the following corn crop. 
 
 In Table 7 the results of the Toledo experiment are summarized. 
 
 TABLE 7. SUMMARY OF CROP YIELDS: TOLEDO FIELD 
 (Bushels per acre) 
 
 Tillage 
 treatment 
 
 Corn 
 9 crops 
 
 Soybeans 
 
 7 crops 
 1 
 
 Wheat 
 6 crops 
 
 Sweet clover 
 seed 
 6 crops 
 
 Plowed 7 in 
 Subsoiled 1 
 Deep tilled 
 Dynamited 
 
 ches deep 
 
 40.2 
 41.9 
 37.4 
 40.3 
 
 16.3 
 16.2 
 15.2 
 16.4 
 
 13.5 
 12.9 
 10.8 
 11.7 
 
 3.68 
 3.65 
 3.18 
 4.25 
 
 i inches deep 
 
 14 inches 
 
 
 SUBSOILING, DEEP TILLING, AND DYNAMITING FAIL TO OPEN 
 UP TIGHT CLAY SUBSOIL 
 
 The fundamental cause of the frequent crop failures, low yields, 
 and relatively low agricultural value of Gray Silt Loam On Tight Clay 
 is the presence of the tight clay subsoil. In the spring the soil is super- 
 saturated. The surplus water which cannot be removed by surface 
 drainage remains until removed by evaporation. This condition results 
 in poor root growth and the crops are very sensitive to the dry, hot 
 weather which commonly follows the spring rains. 
 
164 
 
 BULLETIN No. 258 
 
 [February, 
 
 PLOTS 4 and 8 
 Charges 8' -3" by 8 '-3' 
 
 2 rods 
 
 PLOTS 12 and 16 
 Charges II' by II' 
 
 
 o o o o 
 
 
 XXX 
 
 
 O O O O 
 
 
 XXX 
 
 
 o o o o 
 
 
 XXX 
 
 
 O 
 
 
 XXX 
 
 
 O O 
 
 
 XXX 
 
 
 o o o o 
 
 
 XXX 
 
 
 O O O 
 
 
 XXX 
 
 to 
 
 -o 
 
 
 
 t- 
 
 O O o 
 XXX 
 
 00 
 
 O 
 
 
 XXX 
 
 
 o o o o 
 
 
 xxx 
 
 
 o o o o 
 
 
 xxx 
 
 
 O O O O 
 
 
 xxx 
 
 
 O O O 
 
 
 xxx 
 
 
 o o o o 
 
 
 xxx 
 
 
 O O 
 
 
 xxx 
 
 
 O O O 
 
 o = I st time 
 x - 24 time 
 -3d time 
 
 
 c X 
 
 
 
 X 
 
 
 
 
 O 
 
 o 
 
 
 
 o 
 
 
 c X 
 
 
 X 
 
 
 
 O 
 
 o 
 
 
 
 o 
 
 
 : x 
 
 
 X 
 
 
 
 
 
 o 
 
 
 
 o 
 
 
 : X 
 
 
 X 
 
 
 
 o 
 
 o 
 
 
 
 o 
 
 
 : x 
 
 
 X 
 
 
 <n 
 -a 
 o 
 
 -: 
 
 o 
 : x 
 
 o 
 
 
 X 
 
 o 
 
 00 
 
 o 
 
 o 
 
 
 
 o 
 
 
 \ x 
 
 
 X 
 
 
 
 * 
 
 o 
 
 
 
 
 
 
 : x 
 
 
 X 
 
 
 
 
 
 
 
 
 
 o 
 
 
 : x 
 
 
 X 
 
 ) 
 
 
 
 
 o 
 
 
 
 
 
 
 1 X 
 
 
 X 
 
 1 
 
 
 
 
 o 
 
 
 
 o 
 
 
 L X 
 
 
 X 
 
 5 
 
 
 o 
 
 
 
 
 
 o 
 
 FIG. 4. METHOD OF SPACING CHARGES ON DYNAMITED PLOTS 
 
 The charge was placed well into the tight clay stratum and made as heavy as 
 possible without being so heavy as to blow the soil out and form a hole. 
 
. 19251 SUBSOILING, DEEP TILLING, AND DYNAMITING 165 
 
 That a solution of this problem is not to be found in subsoiling, 
 deep tilling, or dynamiting is indicated by the results of these experi-, 
 ments. Any such treatment to be effective would have to shatter or 
 open up this impervious stratum sufficiently to increase the passage of 
 water thru it and to allow roots to penetrate it readily. The character 
 of the material is such that it is rarely, if ever, dry enough to be shat- 
 tered, and it seems very unlikely that it would remain shattered any 
 length of time even if such a condition could be produced. 
 
 FIG. 5. DEPRESSION FOUND IN THE SPRING OVER EACH SPOT WHERE A 
 CHARGE OF DYNAMITE WAS EXPLODED THE PREVIOUS FALL 
 
 These basins were entirely impervious to water. A subsoil that is 
 plastic in nature cannot be opened up successfully with dynamite. 
 
 The dynamite charges, instead of shattering the tight "clay, formed 
 perfect basins with highly compacted walls which were entirely imper- 
 vious to water. In the spring, the location of every charge of the pre- 
 vious fall was indicated by a small depression. (See Fig. 5.) It appears 
 to be a universal rule that dynamite cannot be used successfully to open 
 up a subsoil which is plastic in nature. 
 
 The term "hardpan" is commonly applied to the tight clay stratum; 
 however, it is very different from true hardpan. True hardpan is not 
 known to occur in Illinois. It is a cemented stratum common in semi- 
 arid regions and it can be broken up successfully with dynamite. Tight 
 clay is not a cemented layer; instead, it is very plastic, due to its high 
 percentage of very fine particles. The effect of the dynamite charges on 
 the plastic clay was harmful, rather than beneficial, as is shown in Fig. 6, 
 and as was shown in the Kansas- work. 
 
166 
 
 BULLETIN No. 258 
 
 [February,. 
 
 In order to get further evidence as to whether the subsoiling, deep 
 tilling, or dynamiting had any effect on the passage of moisture thru 
 the tight clay stratum, samples were taken in the spring of 1919 and of 
 1920 for the purpose of making moisture determinations. It was 
 
 1. 
 
 ---...:---- 
 Mottle^, yellow, {Viable, silty clay loarri';.-.- 
 
 FIG. 6. SKETCH OF SOIL PROFILE FOR GRAY SILT LOAM ON TIGHT CLAY, SHOWING 
 
 THE COMPACTING EFFECT OF EXPLODING A DYNAMITE CHARGE IN 
 
 THE PLASTIC CLAY STRATUM 
 
 thought that if any of these tillage treatments increased the passage of 
 water thru the tight clay stratum, it would be shown in the moisture 
 content of the surface and subsurface during the period of excess 
 moisture in the early spring. 
 
 TABLE 8. PERCENTAGE OF MOISTURE IN SURFACE AND SUBSURFACE: TOLEDO FIELD* 
 
 Plot. 
 
 8 
 
 Tillage treatment Plowed 7 in. Subsoiled Deep tilled Dynamited 
 
 Surface 0-8 Inches 
 
 April 30 
 
 . 29 
 
 4 + 
 
 0.33 
 
 79 
 
 .3 + 0, 
 
 74 
 
 77 
 
 ? + 
 
 0.16 
 
 29.4 
 
 0.27 
 
 May 7 
 
 27 
 
 5 + 
 
 0.35 
 
 77 
 
 .8 0. 
 
 7S 
 
 75 
 
 8 + 
 
 0.22 
 
 29.8 
 
 + 0.18 
 
 May 15 
 
 28 
 
 7 + 
 
 0.50 
 
 78 
 
 .2 + 0, 
 
 75 
 
 ?S 
 
 1 + 
 
 0.25 
 
 29.2 
 
 + 0.21 
 
 May 21 
 
 28 
 
 9 + 
 
 0.28 
 
 78 
 
 .3 + 0. 
 
 77 
 
 76 
 
 1 + 
 
 0.20 
 
 28.4 
 
 + 0.28 
 
 Seasonal average 
 
 28 
 
 .5 
 
 0.19 
 
 28 
 
 .4 + 0, 
 
 ,12 
 
 26 
 
 .1 + 
 
 0.10 
 
 29.3 
 
 + 0.12 
 
 Subsurface 8 Inches to the Tight Clay 
 
 April 30 
 
 . 25 
 
 .0 0, 
 
 44 
 
 22 
 
 9 + 
 
 0.34 
 
 73 
 
 8 + 
 
 0.16 
 
 24.2 
 
 0.26 
 
 May 7 
 
 ' 23 
 
 .3 0, 
 
 40 
 
 77 
 
 t 
 
 0.32 
 
 22 
 
 9 + 
 
 0.20 
 
 24.6 
 
 0.23 
 
 May 15 
 
 . . 24 
 
 .1 0, 
 
 46 
 
 'M 
 
 1 + 
 
 0.30 
 
 71 
 
 7 + 
 
 0.18 
 
 25.1 
 
 + 0.29 
 
 May 21 
 
 26 
 
 .3 0, 
 
 34 
 
 7S 
 
 7 
 
 0.41 
 
 ?<; 
 
 5 
 
 0.27 
 
 25.9 
 
 + 0.18 
 
 Seasonal average 
 
 24 
 
 .9 + 0, 
 
 .20 
 
 23, 
 
 .9 + 
 
 0.17 
 
 24, 
 
 ,o 
 
 0.10 
 
 24.9 
 
 + 0.12 
 
 fourteen samples from each plot on each date. 
 
1925~\ SUBSOILING, DEEP TILLING, AND DYNAMITING 167 
 
 It will be noted by reference to Table 8 that there were no signifi- 
 cant differences in 1920 in the moisture content of the plots which 
 had received the various tillage treatments the previous fall and also 
 in the fall of 1915. It seems apparent that none of the tillage treatments, 
 subsoiling, deep tilling, or dynamiting, had any effect which was re- 
 flected in the moisture content of this poorly drained prairie soil. 
 
 EXPERIMENT AT URBANA: SOIL VARYING FROM BROWN SILT 
 LOAM TO BLACK CLAY LOAM 
 
 In 1915, an experiment on time and depth of plowing was started 
 on the 900 and 1000 series of the University South Farm. The soil on 
 these two series varies from Brown Silt Loam to Black Clay Loam, 
 probably corresponding to Muscatine silt loam and Clyde clay loam as 
 classified by the Bureau of Soils of the United States Department of 
 Agriculture. A four-year rotation of corn, corn, oats, and sweet clover 
 occupies these two series, each crop being grown each year. 
 
 The times and depths of the various plowing operations are shown 
 in Table 9. A two-bottom gang was used for the 3 to 4-inch depth, 
 and the 7-inch depth, and a deep tillage machine for the 12 to 14-inch 
 depth. 
 
 Also in Table 9, the yields of first-year corn are given for the period 
 of the experiment, 1915 to 1920, and the yields of second-year corn for 
 the last four years. 
 
 The results indicate that, in so far as the yield of corn is concerned, 
 there is no choice between 12 to 14-inch fall plowing, 7-inch fall plow- 
 ing, and 7-inch spring plowing, but that 3 to 4-inch spring plowing is 
 apparently too shallow for the best growth of corn. The differences, 
 however, in favor of the deeper plowing as compared with the shallow, 
 are not large enough to be at all conclusive. The consistent character 
 of the results indicates that no increases in yields can be expected on 
 these soil types following plowing to a depth of 12 to 14 inches with 
 the deep tillage machine. 
 
 COOPERATIVE EXPERIMENTS 
 1912 Experiment 
 
 Late in May, 1912, two one-half acre plots were plowed 6 to 7 
 inches deep and two other half-acre plots plowed 12 to 14 inches 
 deep on a farm two miles south of Urbana, on soil which is classified 
 as Brown Silt Loam. Corn was planted within a few days following 
 the plowing, after disking, rolling, and harrowing. The crop yields are 
 given in Table 10. 
 
 This experiment, while inconclusive because of lack of replication 
 and also because but one year's work was done, indicates that plowing 
 to a depth of 12 to 14 inches for corn a few days before planting is 
 
168 
 
 BULLETIN No. 258 
 
 [February, 
 
 C 
 
 a 
 
 .SCO 
 
 CO ^ 
 
 4"* 
 
 S b 
 
 s * 
 
 r! o 
 
 >> 
 
 1o O 
 
 .t-o 
 
 x 
 
 Os so 
 
 si 
 
 11 <J 
 
 -*sSsS 
 
 sS2 
 
 
 a 
 
 .r-^ 
 
 oo\ 
 
 
 CM 
 
 -^ ON ON 
 
 r^* co 
 
 CN 
 
 
 
 so so 
 
 so so 
 
 25 
 
 *.. ex 
 
 . so O 
 
 c ON 
 
 
 co O 
 
 "" CJ 
 
 -if so oo 
 oo oo 
 
 ON oo 
 
 
 a 
 
 .COON 
 
 Tf SO 
 
 
 CM 
 
 ~ ON SO 
 
 -r to 
 
 2 
 
 
 
 so so 
 
 ON 
 
 cx 
 
 . CM O 
 
 ON'* 
 
 
 to O 
 
 H * ^ 
 
 SO CM 
 
 
 1-1 o 
 
 so SO 
 
 to to 
 
 
 a. 
 
 . ON OO 
 
 '-i ON 
 
 
 S 
 
 4? ON -H 
 
 so to 
 
 oo 
 
 ^ o 
 
 Tt<tO 
 
 to to 
 
 ON 
 
 <-, 0. 
 
 .CO Tt< 
 
 oo r-~ 
 
 
 co O 
 
 3 -H CO 
 
 to to 
 
 
 ~* CJ 
 
 so so 
 
 so so 
 
 
 a 
 
 . *o O 
 
 t^-H 
 
 
 CN 
 
 ^ to to 
 
 oo 
 
 J5 
 
 
 
 so so 
 
 SO to 
 
 ON 
 
 ^ cx 
 
 .Ttr- 
 
 ON co 
 
 
 co O 
 
 ^ fM O 
 
 CM'O" 
 
 
 
 
 r^r- 
 
 
 
 CN u. 
 
 
 
 so 
 
 u 
 
 
 
 ON 
 
 xj CX 
 
 . O CM 
 
 ON-i 
 
 
 J3 
 
 
 
 * ' 
 
 
 u 
 
 ~*^^ 
 
 ^rt< 
 
 
 CN In 
 
 
 
 *2 
 
 
 
 
 
 ON 
 
 to 
 
 . O SO 
 
 R*1 
 
 
 ^ U 
 
 -* 
 
 so so 
 
 j 
 t 
 i 
 
 i 
 
 3 
 
 i 
 > 
 
 ." 
 
 r-J 
 
 c 
 
 3 
 
 -i r^ 
 
 
 \ 
 
 .c 
 
 
 
 1 
 
 
 
 
 
 e 
 
 
 
 J 
 1 
 
 i 
 
 i, 
 
 
 
 u 
 
 1 
 
 
 
 
 4 
 
 i 
 
 
 
 j 
 
 
 
 
 
 ^ 
 
 
 M 
 
 .s 
 
 
 
 "re 
 
 C 
 
1925-} 
 
 SUBSOILING, DEEP TILLING, AND DYNAMITING 
 
 169 
 
 harmful on Brown Silt Loam. There is reason to believe it would be 
 equally harmful on any soil. 
 
 TABLE 10. ACRE YIELDS OF CORN GROWN IN COOPERATIVE 
 EXPERIMENT: URBANA, 1912 
 
 Tillage treatment 
 
 Individual plots 
 
 Average 
 
 Plowed 6 to 7 inches deep 
 
 bu. 
 
 67.7 
 
 bu. 
 66.3 
 
 
 64.9 
 
 
 Deep tilled 12 to 14 inches 
 
 63.3 
 
 56.4 
 
 
 59.5 
 
 
 1913 Experiment 
 
 In the late fall of 1912, four one-acre plots were plowed 6 to 7 
 inches deep and four other one-acre plots plowed 12 to 14 inches deep 
 with the deep tillage machine. The next spring the seed bed was pre- 
 pared and the corn planted. Table 11 gives the yields secured. 
 
 TABLE 11. ACRE YIELDS OF CORN GROWN IN COOPERATIVE EXPERIMENT: 
 URBANA, 1913 
 
 Tillage treatment 
 
 Individual plots 
 
 Average 
 
 Plowed 6 to 7 inches deep 
 
 bu. 
 49.1 
 
 47.2 
 
 bu. 
 44.9 + 1.62 
 
 
 40.7 
 42.6 
 
 
 Deep tilled 12 to 14 inches 
 
 47.6 
 43.7 
 
 45.9 + 0.94 
 
 
 44.3 
 48.2 
 
 
 It will be noted that the difference in the average yields is so small 
 as entirely to lack significance, and also that there is considerable dif- 
 ference shown in the yields of individual plots which received the same 
 tillage treatment. This fact emphasizes the necessity of having a suffi- 
 cient number of plots in any work of this sort to give a reasonably re- 
 liable average. By proper selection these figures could be used to prove 
 either that ordinary plowing is superior or that deep tilling is superior, 
 when, as a matter of fact, there is no significant difference shown be- 
 tween the two when measured in terms of the corn crop. 
 
170 BULLETIN No. 258 
 
 THE COST CONSIDERATION 
 
 The merits of any tillage practice are determined by the net re- 
 turns resulting from that particular practice. It costs at least twice as 
 much to subsoil a field as it does to plow it at an ordinary depth. 
 Probably a fair statement is that when it costs $2.50 an acre to plow 
 7 inches deep, it will cost $5 an acre to subsoil, and $1 an acre 
 to deep till. It was found at this Station that it takes four horses to 
 pull a subsoil plow and six horses to pull the deep tillage machine. At 
 Toledo, a two-plow tractor was used for two years to pull the deep 
 tillage machine, and it was overloaded. 
 
 The cost of dynamiting varies considerably because of differences 
 in the costs of material and labor, but it is always high. If the charges 
 are placed at intervals of one rod each way, and one-third stick of 20- 
 percent dynamite is used for each shot, the cost, including labor, will 
 range from $20 to $25 an acre, when dynamite costs 30 cents a pound. 
 It is apparent that very large increases in yield would have to follow 
 the dynamite treatment to justify its use for general farm crops. 
 
 ACKNOWLEDGMENT 
 
 The experimental work described in this bulletin has involved the cooperation of 
 many persons. Special acknowledgment is hereby made to the late Professor J. G. 
 Mosier, and to Professor A. F. Gustafson and Mr. F. A. Fisher, former members of 
 the Agronomy Department. 
 
UNIVERSITY OF ILLINOIS-URBANA