BKOADBALK FIELD DRAINAGE WATERS 233 



through into the drain is very low, so thoroughly have the 

 nitrates been removed by the 'growing crop. From September 

 onwards, however, to February, the concentration of the water 

 is comparatively high, and as the drains begin to run freely 

 during this period when the crop is off the ground, great losses 

 of nitrate are likely to occur. Nitrification goes on throughout 

 the winter ; even in years when the rainfall of the early autumn 

 is so excessive as to wash the soil clean of all nitrates produced 

 during the first nitrification following the removal of the crop, 

 yet fresh nitrates are still produced in considerable quantity, 

 and find their way into the drains in December and January. 

 Nothing, in fact, short of the absolute freezing of the ground 

 stops the production of nitrate and its consequent loss when- 

 ever the rainfall is heavy enough to wash through into the 

 subsoil. 



If the results obtained on the drainage water from the 

 manured plots be examined, it will be seen that nitrification 

 of manures like ammonium-salts is extremely rapid ; if there is 

 any percolation, nitrates begin to appear in the drainage water 

 immediately after the application of the manure. Even in 

 autumn an application of ammonium-salts is converted into 

 nitrate in a very short time, as may be seen from the following 

 series of analyses of the water running from the drain below Plot 

 15, in October 1880. 



On October 25th of that year, mixed ammonium- salts con- 

 taining 86 Ib. of nitrogen and 119 Ib. of chlorine per acre 

 were applied to Plot 15 and ploughed in. Heavy rain followed, 

 so that on October 27th the drain beneath the plot was 

 running; other rain fell at short intervals, and yielded the 

 series of samples set out in the table. It will be noticed 

 that in the first runnings, taken within forty hours of the 

 application of the manure, some ammonia was to be found. 

 This is a very exceptional occurrence, but the large excess in 

 which the chlorine was present in the water showed that the 

 decomposition of the ammonium chloride and retention of 

 the ammonia by the soil had progressed considerably. 



