412 Decomposition of Oi-ganic Matter in Soil 



only slowly mingles with the soil by reason of the high degree with which 

 it is absorbed. There is remarkably little evidence as to the rate of 

 nitrification of sulphate of ammonia in field soils, and more measure- 

 ments are needed. 



The Rothamsted evidence is obtained from the analysis of the 

 drainage water of Broadbalk field and is in some respects more satis- 

 factory than can be derived from direct field determinations. The 

 analyses have not been made as systematically as in the case of the 

 drain gauges because of the difiiculties of sampling, but sufficient", data 

 have accumulated to bring out the general facts. 



The composition of the drainage water from Plots 8 and 10 in 

 Broadbalk Wheat Field before and after the application of ammonium 

 salts was as follows : 



Nitrogen as nitrates per million of. drainage. 



Plot 8 receives complete mineral fertilisers in addition to ammonium 

 salts, while Plot 10 receives in addition superphosphate only, and no 

 potash. Here the marked increase is observed some weeks after the 

 application, but as the drains had not been running in the meantime 

 there is no way of telling at what period between March 1st and 

 April 26th it took place. 



In the autumn measurements the interval is less though it is not 

 clear whether this is due to more rapid action (the soil is certainly 

 warmer) or to more rapid detection because the drains ran at a shorter 

 interval. A small increase in nitrate has been detected only 40 hours 

 after the application of the ammonium salts, but the marked increase 

 did not come for three weeks. 



The salts added are a mixture of ammonium sulphate and ammonium 

 chloride, and the large amount of chloride on Oct. 27th shows that 

 washing out had already begun, so that any nitrate formed could have 

 been detected. 



Laboratory experiments have been made both by Schloesing and at 

 Rothamsted and have shown that action may be practically completed 

 in 8 to 15 days under favourable conditions. 



