222 



NITRIFICATION 



for nitritication occur when the land is subjected to a bare 

 summer's fallow ; the land is being thoroughly worked, the 

 temperature is high through the complete exposure to the sun's 

 rays, and the soil also retains sufficient moisture for nitrification 

 because it is not being dried by the growth of a crop. The 

 favom^able results accruing from a l)are falloAv on strong land 

 have already been discussed, and though they are in part due 

 to the freedom from weeds and the improved tilth of the soil, 

 the main effect must l)e attributed to the accunuilation of 

 nitrates during the summer. 



The following table shoAvs the amount of nitrogen as 

 nitrate found in various Rothamsted soils after fallowing : — 



Table LXXVLI. — Effect of Fallowing — Nitrogen as Nitrates, lli. 2)or acir. 



I 



The accumulation of nitrates in the surface soil of the 

 uncropped land as the summer advances is to be seen very 

 plainly from the figures : the lowest amount of nitrate was in the 

 March sample, and both the July samples were poorer than that 

 drawn in October. In October also the continuous wheat land 

 had been broken up, and nitrification thus started afresh. It is 

 also plain that the fallow land was much richer in nitrates than 

 the plot which had been under continuous crop, although the 

 accumulation of nitrates was greater on the last plot where the 

 land had been manm^ed and was in good condition than on the 

 other plots, all of which had long been unmanured. 



It has already been pointed out in dealing with the wheat 



