Cooperative Work with Columbia University 435 



Comparative Plant Food Value of Nitrogen in Animal and Vegetable 



Materials 



availa- 

 bility 

 OR crop- 

 material containing nitrogen producing 



value 



Sodium nitrate 100 



Ammonium sulphate 95 



Dried blood 70 



Cottonseed meal 70 



Castor pomace 70 



Fish, dried and ground 68 



Horn-and-hoof meal 65 



Leather, dissolved with acid 65 



Leather, steamed 15 



Leather, roasted 10 



Leather, raw 2 



There is, perhaps, not so much saving in money by the home 

 mixing of fertilizer as there once was, but there remains the very 

 great advantage of knowing what you are putting on. And behind 

 that is the educational value of knowing why you are going to put 

 on just what you do. A man can go on for years with purchased 

 brands and know nothing more about fertilizers than the cost per 

 ton and the result, but he cannot mix a solitary batch at home 

 without some consideration of the crop he is to grow and the soil 

 upon which he grows it. 



FORM OF PHOSPHORIC ACID 



There has been considerable controversy over the merits of rock, 

 bone, and acid phosphate. The chief value of the acid phosphate 

 lies in the superior distribution that you get by solution. Bone 

 phosphate has no particular merit. That derived from rock is as 

 good, and usually much cheaper. The Ohio experiments in the 

 use of rock are very instructive. When a soil is rich in organic 

 matter, so that the bacterial processes are rapid and there is much 

 carbon dioxide in the soil water, a long-season crop may do as 

 well with ground rock as with acid phosphate. But the quantita- 

 tive comparison is more fair. For comparison in results, the phos- 

 phoric acid supplied in rock must be three or four times that sup- 

 plied in the acid phosphate. Under the conditions named, and 

 where the former is used in the manure heap, the rock may be the 

 cheaper source.* 



* See Bulletin 187, Agricultural Experiment Station, Lafayette, Ind. 



