310 THE SMALL GRAINS 



must first be slaked by treating it with J its weight of 

 water, covering it with soil, and allowing it to remain so 

 for 2 or 3 weeks before using. 



336. Fertilizers. As previously stated, the plant-food 

 constituents in one or more of which almost all the older 

 agricultural soils are deficient are nitrogen, phosphorus, 

 and potassium. It is therefore necessary to supply these 

 foods in some form or another in order to provide a bal- 

 anced ration for the cereal crop. It has been determined 

 at the Missouri Experiment Station that a 30-bushel crop 

 of wheat to the acre, producing also l| tons of straw, 

 removes from the soil 49 pounds of nitrogen, 7j pounds 

 of phosphorus, and 33 pounds of potassium, and that a 

 60-bushel crop of oats, including if tons of straw, re- 

 moves 55 pounds of nitrogen, 8j pounds of phosphorus, 

 and 39 pounds of potassium. The total cost of ferti- 

 lizers necessary to replace these foods lost from one acre 

 is $11.61 for the oats, and $10.43 for the wheat. 



Nitrogen is furnished by barnyard manure, cottonseed 

 meal, and in nitrate fertilizers, but its principal source is 

 from the air. Cottonseed meal is often employed in wheat 

 fertilizers, but is considered to be less effective and eco- 

 nomical than an equal value of nitrate of soda. Potas- 

 sium is ordinarily present in the soil in sufficient quantity, 

 but is often unavailable, until rendered so by the pres- 

 ence of other substances, such as lime. When absent, it 

 is supplied usually in the form of the mined product 

 kainit . or the manufactured muriate of potash. It is 

 particularly essential in fertilizers intended for light, 

 sandy soils. Phosphorus is generally deficient in the older 

 wheat soils, and must be supplied in the form of acid 

 phosphate, bone meal, rock phosphate, or basic slag. 

 It appears from results of experiments that, in the pres- 



