A STUDY OF CERTAIN GREEN MANURE CROPS IN 

 MAKING ROCK PHOSPHATE AVAILABLE IN SOILS. 



ROSS L. BANCROFT AND B. J. FIRKINS. 



At the present time the world is in the midst of the greatest 

 conflict ever staged. The byword on the lips of every thoughtful 

 American is, ' ' Food will win the war. ' ' In order that food may 

 be conserved it must first be produced. Therefore, increased 

 crop production must be stimulated. We must produce larger 

 crops upon a given area, that is, intensive farming should be 

 practiced. 



Primaiy among the controlling factors in securing increased 

 crop production is an abundant supply of active organic matter 

 and sufficient solulble phosphorus for the entire needs of the grow- 

 ing crop. 



Availalble or soluble phosphorus is obtained commercially by 

 mixing raw phosphate with sulfuric acid. At the present time 

 sulfuric acid is difficult to obtain. Accordingly the idea was 

 conceived of growing a green manure crop on soil to which raw 

 rock phosphate had been applied. By selecting a green manure 

 crop which is able to utilize so-called inert phosphate obtained 

 from raw rock and by plowing the same under, the succeeding 

 crop should derive at least two beneficial effects. In the first 

 place an essential and desirable amount of active organic matter 

 would be supplied to the soil, also a quantit}^ of soluble phos- 

 phorus might be made available for the following crops. 



Accordingly in order to study this problem a miami silt loam 

 soil was selected. This soil contained a small amount of organic 

 matter and an analysis showed the total phosphorus content to 

 be .033 per cent. Ten pounds of this miami soil w^as placed in 

 pots of one gallon capacity. The equivalent of 1200 pounds per 

 acre of Tennessee brown rock phosphate was added to the miaani 

 silt loam soil. Soluble salts containing plenty of the other essen- 

 tial plant foods were added and thus phosphorus was made the 

 controlling element in the crop production. 



The following green manure crops were sown on this soil: 

 buckwheat, Japanese millet, German millet, both bearded and 

 beardless barley, rape, Iowa 103 oats, durum wheat, soy beans, 

 cane, alfalfa, alsike and red clover, cow peas and timothy. Ma- 

 nure crops were allowed to grow for three months and then were 



