SOILS AJND FERTILIZERS 135 



by good methods of cropping and tillage. As a rule, how- 

 ever, the better the soil the better the yield, unless the land is 

 so rich that the crop lodges before it matures, in which case 

 grain of poor quality is sure to be produced. 



The best wheat sections are in that portion of the tem- 

 perate zones where there is an annual rainfall of from 20 to 40 

 inches, distributed quite uniformly throughout the growing 

 season. Wheat, however, is grown in the Pacific states, 

 where most of the rainfall comes during the winter and very 

 little of it during the growing season ; but soils in this section 

 have great water-holding capacity, which enables them to 

 hold the moisture till it is needed by the crop. Wheat is 

 also grown under irrigation with very satisfactory results. 



174. Manures and Fertilizers. Grain is the chief 

 product of the wheat crop. It removes from the farm con- 

 siderable amounts of nitrogen, phosphoric acid, and potash. 

 Of the mineral constituents of wheat the grain contains about 

 50 per cent of phosphoric anhydride and 33 per cent of 

 potash, while in the straw there is only about 3 per cent of 

 phosphoric anhydride and 15 per cent of potash. Most of 

 the soils in the wheat belt have a much larger supply of 

 potash than of nitrogen and phosphoric acid, and as the 

 potash is used more largely in the production of straw, which 

 as a rule remains on the farm, nitrogen and phosphorus are 

 first depleted. Where live stock is kept, clover grown, and 

 the land manured frequently, satisfactory yields of wheat 

 may be obtained on naturally fertile soils for generations 

 without the addition of commercial fertilizers. But where 

 wheat is the main crop or where wheat and other exhaustive 

 crops are grown and land is seldom if ever manured, it ulti- 

 mately becomes necessaiy to add to the soil some kind of 

 commercial fertilizer that will supply the needed elements as 

 they become deficient. Clover may be grown to add nitro- 

 gen, and clover, green manure, and stable manure will main- 

 tain the supply of vegetable matter. Where this practice 



