98 



NITROGENOUS MANURES 



[chap. 



scheme of experiment is to take four plots for each 

 manure ; one receives the manure in any particular year, 

 while the others remain unmanured except for the 

 residues that may remain from a similar application 

 that had been made one, two, and three years pre- 

 viously, a fifth plot continuously unmanured being 

 employed as a check. 



The experiments have not been in progress long 

 enough to enable exact results to be obtained, especially 

 as regards the residues remaining in the second or 

 third year after the application, but the following 

 figures show the kind of return which may be antici- 

 pated. In order to eliminate the effect of season and 

 crop, the increase given by a residue is always compared 

 with the increase brought about by a fresh application of 

 the same manure, which increase is reckoned as lOO. 



Table XXX.— Increased Yield due to residues of Nitrogenous 

 Manures compared with Increase produced in First Year. 

 Rothamsted. 



Thus rape cake, a manure which we have seen to 

 be comparatively active, leaves behind for the following 

 year a very small residue, having only 9 per cent, of 

 the effect of a fresh application of manure ; whereas a 

 wool shoddy increases the crop in the second year by as 

 much as 79 per cent, of the increase produced by a fresh 

 application of the same manure, and even after two 

 crops have been removed the residue is still one-third 

 as effective as a fresh application. 



