IRRIGATION AND DRY-FARMING 715 



able crop, it is sometimes the practice to collect and store 

 the rainfall of two seasons in the soil. This is the system 

 of alternate-year cropping. In the intervening year the 

 soil is carefully fallowed and mulched, to hold the stored 

 moisture. That such long-time storage of available 

 moisture is possible has been clearly demonstrated * under 

 dry-farming conditions, and also in the study of irrigation 

 problems. An arid or a semiarid climate is especially 

 favorable for the formation and maintenance of an effi- 

 cient dust mulch, and the occurrence of dry earth in the 

 lower subsoil permits moisture to be stored and retained in 

 large quantities within reach of the roots of crops. It is 

 believed by some persons that the practice of fallowing 

 in alternate years is very destructive of organic matter 

 in the soil, and that it may be better to grow a green- 

 manure crop in that period to be turned under. It is 

 questionable whether the loss of water may not be a 

 serious objection to this. 



614. Drought-resistant crops. — For growth under dry- 

 farming conditions, crops are preferred which have a low 

 moisture requirement, which are not seriously affected 

 by severe drying, and which have a fairly deep root system. 

 The sorghums come in the first class and also fulfill the 

 second requirement. Corn is fairly satisfactory. Wheat, 

 barley, and alfalfa are favorite dry-farm crops. Drought- 

 resistant varieties of these crops are being sought. A 

 rotation is desirable which exposes the soil as little as 

 possible to evaporation, and permits continuous mulch- 

 ing with the minimum of plowing. 



1 Atkinson, A., Buckman, H. 0., and Gieseker, L. F. Dry 

 Farm Moisture Studies. Montana Agr. Exp. Sta., Bui. 87. 

 1911. Also Burr, W. W. Storing Moisture in the Soil. Ne- 

 braska Agr. Exp. Sta., Bui. No. 114. 1910. 



