134 



SOILS AND FERTILIZERS 



The more rapidly a soil becomes warm in the spring, the 

 sooner will nitrates be formed. Crops like winter wheat 

 will often begin growth before the soil is sufficiently warm 

 to admit of the rapid formation of nitrates and, as winter 

 rains will have leached from the soil nitrates that accumu- 

 lated during the preceding year, the plants often suffer 

 seriously from lack of nitrogen. 



It is not often that the soil for several inches below 

 the surface becomes hot enough, even in midsummer, to 

 interfere with nitrate formation. Crops that make their 

 growth in late spring or summer are not likely to suffer 

 for nitrates unless the total supply of nitrogen is deficient. 



171. Effect of sod on nitrate formation. — In soil on 

 which there is a good stand of grass very little nitrate is 

 ever found. Sod apparently has a depressing influence on 

 nitrate formation. On the same type of soil as that used in 

 the experiment last described, the average quantities of 

 nitrates for each month of the growing season in the surface 

 eight inches of sod land, as compared with corn land under 

 the same manuring, were as follows : 



Table 31. — Nitrates in Soil Under Sod and Under Corn 



There was more nitrogen contained in the corn crop than 

 there was in the timothy crop, so that the larger quantity 



