222 



NITRIFICATION 



for nitrification 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 

 favourable results accruing from a bare fallow 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 be attributed to the accumulation of 

 nitrates during the summer. 



The following table shows the amount of nitrogen as 

 nitrate found in various Rothamsted soils after fallowing : 



TABLE LXXVII. Effect of Fallowing Nitrogen as Nitrates, Ib. per acre* 



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 manured and was in good condition than on the 

 other plots, all of which had long been unmanured. 



* 1 have retained these figures (obtained by VVarington) for their historic 

 interest. More extended recent observations confirm them. (See p. 239 for 

 References.) 



