362 



THE PRINCIPLES OF SOIL MANAGEMENT 



extent of decomposition of organic matter. A soil poor 

 in humus, and which has not been treated with farm 

 manure or green manure, is not likely to respond very 

 strongly to an application of raw phosphate. The fact 

 that superphosphate is available under these conditions 

 is likely to lead to its use without any attempt to im- 

 prove the humus-content of the soil, and thus increase 

 those difficulties that arise from a deficiency of organic 

 matter. It is this condition that makes it necessary 

 to constantly increase the dressings of fertilizer in order 

 to maintain productiveness. 



Experiments by Thorne have shown that the use of 

 farm manure in conjunction with raw phosphates serves 

 to increase greatly the availability of the latter. In 

 these experiments stall manure was used at the rate of 

 eight tons per acre, in one case alone, and in another 

 in connection with 320 pounds of rock phosphate. 

 The manures were applied to clover sod, and plowed 

 under for maize in a rotation of corn, wheat and clover. 

 In the following table, average yields from the manured 

 plats and from the unmanured ones are given. 



Table L 

 Effect of Stall Manure on Availability of Rock Phosphate 



