no TILLAGE— MOVEMENTS OF SOIL WATER [chap. 



Down to the depth of 54 inches the plot receiving 

 minerals and ammonium salts contained 200 tons, and the 

 plot receiving minerals and nitrate 325 tons, less water 

 than the unmanured plot, quantities in this case some- 

 what less than would be indicated by the amount of 

 dry matter produced. 



There are two important cases in which the drying 

 effect of vegetation needs to be taken into account, in 

 the use of catch crops and in the planting of fruit trees. 

 On the lighter lands of the south of England catch 

 crops are not uncommonly taken on the land before 

 roots. The stubbles are quickly broken up, and 

 vetches, trifolium, or rye, are sown in time to make a 

 start while the land is warm, and to be either cut green 

 or fed off before the land is wanted for turnips in the 

 following spring. The advantages of the practice are 

 that the summer-formed nitrates in the stubble-ground 

 are saved from washing out, and that a valuable bite of 

 early fodder is obtained : with the leguminous crops also, 

 the farm is enriched by the nitrogen gathered from the 

 atmosphere. The difficulty of getting catch crops lies 

 in the fact that the stubble ground is left very dry by 

 the preceding crop, so that a timely rainfall is needed to 

 obtain a plant. The danger of their use is that they 

 may so deplete the available soil water as to give the 

 succeeding crop of roots a very poor chance of germin- 

 ating or growing well. In America the practice has been 

 suggested of sowing some leguminous crop like clover 

 in the tillage orchards about the end of July, so that the 

 new surface crop should so dry the ground as to forward 

 the ripening of the apples on the trees; again, any 

 second growth of the trees due to a late summer rainfall 

 would be prevented, this moisture being dealt with by 

 the catch crop. 



The second illustration worthy of notice is that fruit 



