60 



An Account of the Soil 



[PT. I 



in a warm moist autumn. Typical results are shown in 

 the curve of Fig. 15. In a dry summer the nitrate 

 formed is all left in the soil or taken by the crop : in a 

 wet summer some of it is washed out. This is shown 

 by comparing the amounts of nitrate present on an un- 

 manured fallow plot at Rothamsted during the wet 

 summer and autumn of 1912 with those present in the 

 dry summer of 1 9 13 . In the top 1 8 inches of soil amounts 

 were found equivalent to the following quantities of 

 nitrate of soda, in lbs. per acre, showing a very great 

 difference in favour of a dry summer : 



March Apl. May June July Aug. Sept. 



Fig. 15. Curve showing average amounts of nitrate present in 

 cropped soils at different seasons of the year. (Rothamsted.) 



The nitrates left in the soil at the end of September 

 represent the initial stock for the farmer during the 

 coming season. After a dry summer it is high, after a 

 wet one low. How much of it ever gets into the crop 

 depends on the winter weather. A wet winter will wash 

 much of it out while a dry winter conserves it safely. 



