164 POMOLOGY 



It is further stated that at no time during the four years 

 in which the investigation was in progress did the soil sam- 

 ples in the sod plots show more than 14.78 parts nitrates 

 per million of dry soil, while under clean tillage they were 

 as high as 63 in some cases, and where a cover-crop was 

 plowed in they occurred as high as 132, although the average 

 for the plots is not in this proportion. 



138. Is nitrification retarded under sod? — Since the 

 grass is making use of large amounts of nitrates in a sod plot, 

 it is but reasonable to concede that the quantity, as deter- 

 mined by analysis, would be low, although nitrates may be 

 formed as readily there as when the soil is cultivated. 



In order to arrive at some conclusion on this point, ob- 

 servations were taken on the sod plot in the above experi- 

 ment. A small plot three feet square was selected very near 

 to the point where the soil samples had been taken each 

 year previously and the sod was carefully removed without 

 stirring the soil beneath. Another plot of equal size was 

 selected close to the first and after the sod was removed it 

 was spaded to the depth of the surface soil and subsequently 

 cultivated with a hoe weekly. This gave three conditions 

 within the original sod plot: (1) sod; (2) bare unshaded 

 soil; (3) cultivated soil. While the bare soil would not rep- 

 resent the exact conditions under sod, yet it seems to be 

 as near as is practical to obtain in the field. There was 

 practically no difference in soil-moisture at the time these 

 observations were made. The results would seem to indi- 

 cate that, under the conditions obtaining in this experi- 

 ment, nitrification progressed much more rapidly under 

 tillage than when the land is iii sod or bare and uncul- 

 tivated. 



