13 



nurse crop for clover and grass, the possibility of either fall View 

 or spring sowing, the comparatively early ripening of the 

 crop, the fertility of the soil, and other conditions. 



Hoed crops and summer fallow, especially if cultivated, 

 tend to leave a greater quantity of water in the soil than 

 growing broadcasted and uncultivated crops, such as the 

 small grains, In a dry season, for this reason, wheat after 

 corn or cultivated summer fallow is likely to give a much 

 better yield than if grown after wheat or oats. On some new 

 soils wheat sometimes is grown for several years in succession 

 on the same land, but continuous cropping experiments have 

 shown that after a series of years the yields begin to decline, 

 and rotation experiments have indicated clearly that better 

 yields are obtained from soils under rotation than those 

 growing wheat year after year. 



IRRIGATION AND RAINFALL. 



Successful wheat culture does not depend so much upon 

 the total annual rainfall as upon the amount of moisture the 

 soil furnishes the crop during the growing period. The total 

 rainfall in some of the wheat-growing localities of the West and 

 Northwest ranges annually from 12 to 18 inches and yet 

 good crops are produced without irrigation; but in other sec- 

 tions the same amount of rainfall is insufficient for a profit- 

 able yield. Again, in many humid regions where the yearly 

 precipitation is as much as 40 inches, most of the water runs 

 off in the drainage, less than half of the total precipitation 

 being available to the growing plants. The question, therefore, 

 is not alone how much rainfall there is, but how much of it is 

 retained by the soil for the use of the crop. The relation of 

 rainfall to wheat culture is largely a question of soil condi- 

 tions. It is a significant fact that a very large proportion of 

 the wheat of the world, as well as a superior quality of grain, 

 is produced in rather dry regions or on lands subject to ex- 

 tremes of temperature and drought. 



Wherever or whenever the rainfall is deficient, irrigation 

 generally insures a crop and secures larger yields and better 

 grain. It must be practiced judiciously, however, to be 

 successful. Furrow irrigation is considered best in some 30 

 sections and flooding in others. Irrigation sometimes has a 

 marked influence on the composition of the grain. At the 

 time the kernel is filling out, the soil should be properly sup- 

 plied with moisture to promote the production of full and 31 

 plump grain. Too much water at this period has a tendency 32 

 to yellow the crop, retard its maturity, and lower the yield. 



