SPECIAL FARM TOPICS 227 



The monthly distribution of the rainfall in the Western States 

 can be divided roughly into three types the summer rainfall of 

 the Great Plains, the winter and spring rainfall of the Inter-moun- 

 tain district, and the winter rainfall of the Pacific Coast region. In 

 the Pacific Coast region the rainfall occurs almost entirely during 

 the winter months, and the summer months are very dry. In the 

 Inter-mountain region the maximum precipitation occurs during 

 the late winter and spring months. 



In the Great Plains the monthly distribution of the rainfall is 

 quite different from that of the Intermountain region, the greatest 

 monthly rainfall occurring in June, July and August. Summer 

 tillage for moisture conservation is not so well adapted to this region. 

 The frequent rains during the summer months repeatedly pack the 

 surface mulch on the summer-tilled land. This requires frequent 

 cultivation in order to avoid the loss of water by evaporation, and 

 so increases the expense of maintaining the mulch. Owing to the 

 high evaporation in the Great Plains during the summer months, 

 very little water will be stored in the summer-fallowed land unless 

 the mulch is carefully kept up by thorough cultivation after every 

 rain. The higher annual precipitation in the Great Plains and the 

 increased cost of maintaining a good mulch on summer-tilled land 

 have thus combined to make summer fallowing in this region much 

 less popular than in the Great Basin country. Furthermore, the 

 blowing of the dry surface mulch of the summer fallow sometimes 

 becomes very serious in the Great Plains owing to high winds. 



For the above reasons annual cropping is largely used in pref- 

 erence to summer tillage in the Great Plains, although in some 

 parts of the area summer-tillage methods are considered necessary 

 to insure sufficient moisture, even at the cost of the increased labor 

 necessary to maintain the surface mulch. Spring grains are gen- 

 erally used under the annual cropping method, since the crop escapes 

 the dry fall and winter, and the land, having been recently worked, 

 is in the best condition to absorb the summer rainfall. The shade 

 of the growing crop partially protects the ground from excessive 

 loss of water by evaporation, while the small summer showers that 

 are useless on summer-tilled land always help the growing crop. 

 Thus we have a radically different system of farm practice in the 

 Great Plains from that found in the Intermountain country, owing 

 in part to the difference in the distribution of the monthly rainfall 

 of the two regions and in part to the greater rainfall in the Great 

 Plains. 



The way in which the rain comes has a great deal to do with its 

 usefulness. Summer-fallowing methods, for example, are not well 

 adapted to regions in which the rainfall comes largely in the form 

 of little showers from one-tenth to one-half inch. Rains of this 

 kind penetrate the soil only a few inches, and the water is practically 

 all lost through subsequent evaporation even when the surface of 

 the soil is cultivated after the rain, since the rainfall does not pene- 

 trate below the depth of the mulch. These small rains are, however, 

 usually sufficient to pack the mulch and form a surface crust, which 



