410 Decompositioyi of Organic Matter in Soil 



in June and July, and a very marked rise to 1-9 % in August. After 

 this there is a sudden fall to 0-3 % in September and October, followed 

 by a rise to 0-5 % in November. 



The nitrate curve shows the same fluctuations as the COg curve till 

 June, and again from early August onwards. It rises sharply in April 

 to 88 lbs. per acre of nitric nitrogen in the top 18 inches, then falls to 

 66 lbs., rises to 75 lbs., drops and rises, and then falls in two abrupt 

 steps to 38 lbs. in July. Then it rises to 72 lbs. in August, keeps con- 

 stant in September, rises in October to nearly 90 lbs. and falls from 

 this level in November. The maximum difference between the cropped 

 and the fallow plot is in September, when the fallow contained 170 lbs. 

 and the cropped only 70, a difference of 100 lbs. per acre in the top 

 18 inches. By December all this difference has been lost and both 

 have fallen to the same level (Fig. 8). 



In previous years the highest quantity of nitric nitrogen recorded in 

 parts per million had been 18 : this year the peaks on the curve are at 

 20 although in one case we found 25. 



As before, the nitrate curve is like that for bacterial numbers but 

 about three weeks later : the exception is at the time of the very high 

 COg content when the numbers are low. 



Great Harpenden Field (Fig. 5). 



In general condition this comes between the Broadbalk unmanured 

 and the Broadbalk dunged plots : it is farmed in the ordinary way ; it 

 carried potatoes in 1913 when it was dressed with dung and artificials, 

 wheat in 1914 without manure, and oats in 1915 with a spring dressing 

 of 1 cwt. sulphate of ammonia and 2 cwts. superphosphate per acre. 

 Observations were made here to see how far the relationships observed 

 on the Broadbalk plots would be likely to hold under ordinary soil 

 conditions. 



In the main the fluctuations are very similar to those of the Broad- 

 balk plots : as compared with the dunged plot, there are the same rises 

 in April and May, and the same violent outpouring of COo in July and 

 .4ugust. Up till July the curves are flatter than on the Broadbalk 

 dunged plot, and by themselves do not show so close a relationship with 

 the rainfall curves. But when placed alongside of the Broadbalk curves 

 it becomes obvious that the same relationships with rainfall exist but 

 they are less pronounced. 



On the Broadbalk unmanured plots the flattening out process begun 



