SOIL MOISTURE AND DRY FARMING 91 



pitious time, that is, when the soil has dried enough to 

 prevent it from sticking to the harrow, but not enough 

 to cause it to crumble into particles too fine. Of course 

 in practise this cannot always be done when very large 

 areas are to be harrowed. 



The chief use of the mulch is 'to prevent the loss of 

 soil moisture. This loss is far greater in the upper layer 

 of the soil than in those layers that are lower, hence the 

 great importance of maintaining the soil mulch on sum- 

 mer tilled lands. But it may also serve to aid in the 

 increase of the moisture content of the soil, and in put- 

 ting the soil in a condition that will favor the active 

 working of the bacteria that inhabit the same. The first 

 result follows from the added moisture through rain, 

 which, because of the tillage, finds easy penetration into 

 the soil. The amount of such accumulation will be pro- 

 portionate to the amount of precipitation, and to the 

 effectiveness of the measures for preventing its escape. 

 All the moisture that enters the soil cannot be saved, but 

 a very large proportion of it can, as much in some in- 

 stances as 50 per cent. The second follows from the 

 moisture thus maintained in the soil and the aeration 

 given. 



In some soils and under some conditions, the drying 

 of the surface soil is so rapid and complete that this in 

 itself forms a mulch, so to speak, through which moisture 

 cannot pass up from below.' This explains why moist 

 soil may sometimes be found under soil that is quite 

 dry on the surface. Such a condition may also be brought 

 about where the temperature is high, the sunshine abun- 

 dant and the relative humidity low. 



The results that follow the judicious cultivation of 

 growing crops are virtually the same in kind as those 

 that follow the maintenance of the soil mulch on land 

 that is fallow. The cultivation is given with the har- 

 row when applied to cereals and with both the harrow 



