100 DRY LAND FARMING 



more deeply than would otherwise be possible. But 

 beneficial as subsoil moisture is to growing crops, there 

 are limitations as to the extent to which it should be 

 drawn upon. The idea has prevailed that the large yields 

 in the Canadian west are the outcome of moisture lib- 

 erated gradually in the subsoil by the melting of the 

 frost of winter as summer advances. It would be claim- 

 ing too much to say that no advantage results to the 

 crop from this source, but it is correct to say that the 

 chief advantage to the crop comes from moisture that 

 has been stored in the soil and subsoil the previous sum- 

 mer, and as the outcome of the nitrates which the sub- 

 soil moisture contained. 



Under some conditions, from 50 to 90 per cent, of 

 the precipitation that falls may be stored in the soil and 

 subsoil. The larger percentage, of course, goes to the 

 surface soil. Much of the water stored in the surface is 

 drawn upon by the crop in the early stages of growth. 

 The question naturally arises, how much of the moisture 

 stored in the subsoil should be drawn upon in the grow- 

 ing of crops and how much should be left because of 

 the influence which it exerts on the accumulation of 

 subsoil moisture. The larger the quantity of water in 

 the soil in the autumn, the more 'quickly will the winter 

 and spring precipitation go down, and the greater will 

 be the store of the accumulation. It is very evident, 

 therefore, that it would be unwise to follow a system 

 of tillage that would at any time exhaust the soil of its 

 supply of subsoil moisture. Experiment has shown that 

 when moisture is maintained in the subsoil, the tendency 

 is to increase in such moisture. More especially is this 

 true in areas where much of the precipitation falls in the 

 winter. Subsoil moisture is sometimes drawn upon to 

 no good purpose. 



Moisture from the subsoil is drawn upon to no good 

 purpose when the supply is insufficient to properly ma- 



