148 DRY FARMING 



cedure can with profit be followed on all fields. The 

 actual causes of low yield on a given field must first be 

 determined and then the cultural treatment that is likely 

 to control these particular causes must be given, if the 

 largest net advantage to the farmer is to be derived. 

 ■ 120. The Control of Soil Moisture. — The low moisture^ 

 content of the soil is the principal cause of low yields on 

 stubble land. "A dry season'', "too little rain", "hot 

 winds" are generally given as causes of partial failure. 

 So far as this portion of the general problem of manag- 

 ing stubble fields is concerned only two things can be 

 done — (1) endeavor to prevent the moisture already in 

 the soil from escaping, and (2) try to get more in. 



The moistutre in stubble land escapes in only two 

 ways — by evaporating directly into the air and by 

 being transpired by weeds or other volunteer plants 

 growing on the land. The loss by evaporation from 

 most stubble fields in dry climates is very little, prob- 

 ably not sufficient to warrant any but the cheapest form 

 of tillage or mulch making, if for this purpose only. The 

 loss of moisture through the growth of weeds is very 

 great and this can and should be controlled by killing 

 the weeds when they are small. 



Getting additional moisture into stubble fields in fall 

 and spring is a more difficult problem in this climate 

 than keeping in what may be already there. Our 

 autumn, winter and spring seasons are dry. In the 

 seven months from September to March, inclusive, only 

 about one-third of the year's precipitation falls, and a 

 large portion of this is in the form of snow and, there- 

 fore, not easily controlled. To prevent the "run off" in 

 spring, plowing is preferable to surface cultivation or 

 no cultivation, and fall plowing is better than spring 



