Nitrates in Soils. 



105 



being higher the following May than they were August 22 

 before. 



121. Nitrates on Fallow Ground in Spring Compared with 

 That not Fallow. Comparing the mean amount of nitric 

 nitrogen in nine field plots bearing crops in 1899 with that 

 of the nine fallow plots of the same year, as found in the 

 spring of 1900, the amounts are as stated in the table below 

 and represented graphically in Fig. 33. 



Table showing the differences in the amounts of nitric nitro- 

 gen after the winter and early spring rains in ground kept 

 fallow and free from weeds the previous season and that 

 bearing crops. 



From this it is clear that the crops on the fallow ground 

 start out in the spring under conditions very superior to 

 those on the fields which had not been fallow, there being 

 245.68 Ibs. of nitrates more per acre in the surface four 

 feet. 



122. Development of Nitrates Influenced by Depth and 

 Frequency of Cultivation. When a series of cylinders like 

 those represented in Fig. 58, p. 187, are mulched by stir- 

 ring at different depths and the stirring is repeated at dif- 

 ferent intervals the rate of formation of nitrates is ma- 

 terially modified, as shown in the table below : 



Difference in the amount of nitric nitrogen, after 258 days, due 

 . to differences in depth and frequency of cultivation. 



