5o6 



Journal oj Agricultural Research 



Vol. VI, No. 13 



Table XV. — Dry matter produced in cowpeas by Tennessee brown rock phosphate with 

 the addition of dextrose and calcium carbonate — series lo 



a Soluble phosphate. 



b In pots 21 and 22 potassium chlorid was substituted for potassium sulphate. 



Under the conditions of this experiment", fermenting dextrose was a 

 failure in bringing about the liberation of phosphorus. Since the use 

 of crop residues is a common farm practice for supplying organic matter, 

 which is said to aid in the liberation of phosphorus, the series next re- 

 ported was planned with timothy hay and clover substitutes for dextrose. 



Timothy and clover cultures on which data are reported in Table III 

 are used for this phase of the problem. Of the duplicate pots the hay 

 from one was taken for analytical study, while the product of the other 

 was ground and returned as organic matter. This series (Table XVI) 

 shows the original treatment with the quantity of air-dried hay turned 

 under. The contents of the pots to which organic matter was added 

 were turned out and the ground material thoroughly incorporated with 

 the sand on December 3, 1914. On January 23, 1915, the pots were 

 planted to the respective crops. They were harvested on April 17, 191 5. 



The organic matter with phosphate in the above series gave larger 

 returns in most cases than where the phosphate was alone. This increase 

 is probably due to the liberation of phosphorus by the decaying residues 

 or the organic phosphorus in the crop residues themselves. 



