SOIL SESSION. 125 



gray silt loam forty, such crops of corn would require as much phos- 

 phorous as is contained in one acre to a depth of seven inches, and the 

 stock decreases as we go down. In the field, the application of potassium 

 on the brown silt loam does not affect the yield of corn, but steamed 

 bone meal, supplying phosphorous, increases the yield from ten to eigh- 

 teen bushels per acre. On the gray silt loam, which is naturally a wheat 

 soil rather than a corn soil, the same application of steamed bone meal 

 gives an increase of ten to twenty bushels in the yield of wheat. On 

 these soils, comprising about eighty per cent of Illinois soils, phosphor- 

 ous is the limiting element of plant food ; that is, when the season, the 

 rainfall, the rotation and the seed used are such as to insure a maximum 

 crop, the shortage on phosphorus may hold the yield down. In peaty 

 swamp soils, on the other hand, the supply of potassium is short, while 

 the phosphorus content is almost twice that of the brown silt loam. 

 Field results on this soil show no increase from the use of steamed bone 

 meal to supply phosphorus, while $2.50 worth of potassium sulphate has 

 increased the yield from less than ten to sixty and seventy bushels of corn 

 per acre. (See plate one.) 



In the sandy soils and on the red silt loam hill land we find, by chem- 

 ical analysis, still another condition, a shortage first of all in nitrogen. 

 On these soils dried blood to supply nitrogen or legumes plowed under, 

 thus drawing upon the atmospheric nitrogen, increases the yield. By 

 this means alone the yield of corn has been increased from twenty-five or 

 thirty bushels to fifty and sixty bushels. Neither phosphorus nor potas- 

 sium alone affects the yield of corn on these soils. But after the yield has 

 been brought up to fifty and sixty bushels by the use of legumes, as 

 clover or cowpeas, then it tis likely that phosphorus, which is somewhat 

 low, can be profitably used. In fact, steamed bone meal will now in- 

 crease the yield of wheat profitably upon the red silt loam. 



It is esential, then, that we have some knowledge of the plant food 

 content of our soils, which may limit the crop yield and then adopt and 

 follow a system of farming which will maintain, and, when necessary, 

 increase the supply of any element. 



Let me call your attention to the results of different systems of 

 farming, as obtained upon the brown silt loam of the Illinois corn belt. 

 Some of these fields have been under definite experimentation for twenty- 

 seven years. 



The figures showing the yields, all represent the average of the last 

 three seasons, with the exception of the forty-three bushel yield, v/hich 

 is the average of two corn crops during the past three seasons, and the 

 fifty-nine bushel yield, which is for the single year 1904. The 1904 



