18 



FOR BETTER CROPS 



It will be seen that the addition of nitrogen or potassium, 

 separately or together, produces little benefit and sometimes 

 the effect is a decrease in yield, although nitrogen did appre- 

 ciably increase the yield of oats in 1904. After phosphorus has 

 been applied, then nitrogen can be utilized with marked benefit. 



Phosphorus produced a large increase in each crop even when 

 applied alone, but when applied after nitrogen the increase was 

 exceedingly marked, amounting to 18 bushels increase in corn, 15, 

 in oats, and 20 bushels increase in the yield of wheat. While 

 nitrogen was applied in commerical form (dried blood) in these 

 experiments, these results emphasize the very great importance 

 of using phosphorus in connection with clover and farm manure 

 for improving this soil. 



The use of commercial nitrogen was discontinued after 1905, 

 but the addition of phosphorus produced 1.07 tons more clover 

 in 1906, 19 bushels more corn in 1907, 12.2 bushels more corn in 

 1908, and 10.2 bushels more oats in 1909. 



The possible effect of phosphorus on the clover crop itself 

 may be seen in the results obtained in 1905 on the University of 

 Illinois soil experiment field at Urbana, Illinois, which is also 

 situated on good Illinois prairie soil. By "legume" treatment 

 is meant the growing of a catch crop of cowpeas or clover in 

 the corn when it is "laid bv." 



Crop Yields in Soil Experiments 

 Typical Corn Belt Prairie Soil, near Urbana, Illinois 



It will be seen that previous to the beginning of this soil 

 treatment, the last five plots yielded no more than the first five; 

 but after four years of soil treatment, the yield of clover was 

 only 1.23 tons without, phosphorus, while 3.12 tons of well field- 

 cured clover hay were produced where phosphorus had been 

 applied. The effect of potassium was slight. 



