III.] 



HYGROSCOPIC MOISTURE 



87 



In each field the upper layer of soil possesses a 

 higher capacity for retaining hygroscopic moisture than 

 does the lower layer, but in field C. this upper layer is 

 thicker than in field B. It will be seen from the table 

 that as regards total water there is no great difference 

 between the two fields, but when the hygroscopic 

 moisture is deducted, B. contains 3-4 per cent more 

 water available for the plant This difference was 

 manifested in the following season in the yield, which 

 was only 2160 lbs. of grain and straw on C. and 9200 

 lbs. on B. 



Though it is doubtful if the hygroscopic moisture 

 gathered by the surface soil in the cooler and damper 

 periods of the night, can be passed on to the subsoil and 

 given up to the roots, yet by its evaporation the next 

 day it may help to keep the temperature of the soil 

 down, and so indirectly diminish the loss of water to the 

 soil. Of course in certain conditions of air and soil 

 temperature there is condensation upon the soil of visible 

 water which can be available to the crops ; for example, 

 in some months drain-gauges yield more water than the 

 rainfall, though a certain amount of loss by evaporation 

 must also have taken place. This usually happens in 



