26 



EXPEEIMENT STATION EECORD. 



development of nitric nitrogen in them is more rapid than after other crops, hke 

 oats and corn." Tlie soil stirred once a week developed more nitric nitrogen than 

 th?t stirred once in 2 weeks, but there is no evidence that tillage exerted any- 

 notable influence in increasing nitrilication or the formation of soluble salts in the 

 soil below the stirred layer. 



The influence of the frequency and depth of tillage on the nitric nitrogen and 

 soluble salts was studied on uniform clay loam, using the cylinders described in a 

 previous report (E. S. R., 12, p. 521). The experiment was begun in December, 

 1899, and lasted 258 days. The amounts of nitric nitrogen in the surface foot in the 

 cylinders at the close of the 258 days were as follows: Not cultivated, 325.48 lbs. per 

 acre-foot; cultivated once a week, 1 in. deep, 217.60 lbs.; cultivated once a week, 

 2 in. deep, 323.4-4 lbs.; cultivated once a week, 3 in. deep, 441.24 lbs.; cultivated 

 once a week, 4 in. deep, 387.96 lbs.; cultivated once in 2 weeks, 1 in. deep, 213.29 

 lbs. ; cultivated once in 2 weeks, 2 in. deep, 199 lbs. ; cultivated once in 2 weeks, 3 

 in. deep, 401.68 lbs.; cultivated once in 2 weeks, 4 in. deep, 245.26 lbs. 



The nitric nitrogen was determined August 22, 1899, and April 30, 1900, in the 

 first, second, third, and fourth foot of soil of 9 fallow plats described in a previous 

 report (E. S. R., 12, p. 31), which were surrounded by trenches and raised border 

 at the beginning of winter to prevent washing and to secure as much leaching as 

 possible from the natural precipitation. The results show "that there was more 

 nitric nitrogen in the soil at the beginning of May, 1900, than was found after being 

 cultivated every week or 2 weeks from May, 1899, until August 22 of that year with 

 no crop on the ground." 



"If an average of the amounts of nitric nitrogen found in the surface 4 ft. of the 

 9 field plats in the spring is compared with the amounts found in the upper 4 ft. of 

 the 9 fallow plats, they will stand as given in the table below: 



The differences in the ainounts of nitric nitrogen in fallow ground and in that hearing crops 

 after the vnnter and early spring rains. 



[In pounds per acre. Calculated to dry soil.] 



Studies of the seasonal changes of nitrates and other soluble salts were continued 

 during 1900 with crops covering the entire surface, so that intertillage could not be 

 practiced, and with cultivated crops. The studies began in April, just after the frost 

 had left the ground, and continued until September 19, when most of the crops had 

 completed their growth. The combined results obtained are shown graphically. 

 The nitrates increased rapidly in the surface foot of the cultivated ground until 

 July 1, then fell rapidly until August 1, when the crops were making the most 

 rapid growth. From this date they rose slowly until corn was cut, September 1, and 

 then more rapidly until September 19, when the last observations were taken. With 

 uncultivated crops, such as clovers, on the other hand, the nitrates of the first foot 

 increased much more slowly, reaching a maximum June 1, or a month earlier, then 

 declining slowly, reaching a minimum on August 1, after which they again rose until 

 the end of the season. The most rapid increase in nitrates in case of the corn and 

 potato soil occurred in the surface foot. When, however, the crops came into vigor- 

 ous growth, the nitrates in the surface soil were rapidly reduced. Similar, but less 

 marked, fluctuations occurred in case of the uncultivated crops — clover, alfalfa, and 

 oats. 



