ILLINOIS FIELD EXPERIMENTS 463 



for many years under a system of tenant farming, and the soil had 

 become somewhat deficient in active humus. While phosphorus 

 was the limiting element of plant food, the supply of nitrogen be- 

 coming available annually was but little in excess of the phosphorus, 

 as is well shown by the corn yields for 1903 when phosphorus pro- 

 duced an increase of 8 bushels, nitrogen without phosphorus pro- 

 duced no increase, but nitrogen and phosphorus increased the yield 

 by 15 bushels. 



After six years of additional cropping, however, nitrogen appeared 

 to become the limiting element, the increase in 1907 being 9 bush- 

 els from nitrogen and only 5 bushels from phosphorus, while both 

 together produced an increase of 33 bushels of corn. By comparing 

 the corn yields for the four years, 1902, 1903, 1906, and 1907, it 

 will be seen that the untreated land has apparently grown less pro- 

 ductive, whereas on land receiving both phosphorus and nitrogen 

 the yield has appreciably increased, so that in 1907, when the un- 

 treated rotated land produced only 34 bushels of corn per acre, a 

 yield of 72 bushels, or more than twice as much, was produced 

 where lime, nitrogen, and phosphorus had been applied, although . 

 these two plots produced exactly the same yield (57 bushels) in 

 1902. While the actual yields might be quite different under dif- 

 ferent seasonal conditions, the relative and increasing differences 

 between the plots must be considered as representative and due 

 to the difference in soil treatment. 



By comparing plots 101 and 102, and also 109 and no, will be 

 seen the increase by lime, suggesting that the time is near when 

 lime also must be applied to these brown silt loam soils. 



Because of the tremendous importance of this most common corn- 

 belt soil to American agriculture and to the prosperity of the na- 

 tion, space is taken to insert Table 88, giving all of the results thus 

 far obtained from the Bloomington soil experiment field, which is 

 also located on the brown silt loam prairie of the Illinois corn belt. 

 (Additional data are inserted on page 475.) 



The general results of the seven years' work on the Bloomington 

 field tell the same story as those from the Sibley field. The rota- 

 tions differ by the use of clover and cowpeas in 1906, and in dis- 

 continuing the use of commercial nitrogen after 1905, on the 

 Bloomington field, in consequence of which phosphorus without 



