324 



SYSTEAIS OF MANURING CROPS 



[chap. 



of nitrogen removed in the crop from each piece of 

 land was estimated as follows : — 



Table XCIV.— Gain of Nitrogen by Clover Crop, 

 rothamsted. 



Thus, although 151 lb. per acre of nitrogen was 

 removed in 1873 from the clover portion of the field, as 

 compared with 37 lb. from the barley portion, the former 

 in the following year yielded an extra 20 bushels of 

 barley. 



As to the manurial treatment of clover, it is difficult 

 to quote very extensive experiments, because of the 

 failure of the plant which takes place through clover 

 " sickness." On the best clover soils in this country it 

 cannot be grown more frequently than once in four 

 years, and more often once in seven or eight years only 

 is safe. The Rothamsted experiments all go to show 

 that manuring alone will not keep off clover sickness, 

 though it was found possible to maintain a long succes- 

 sion of clover crops on a small patch of rich garden soil. 

 Lime and potash salts are helpful but cannot be trusted 

 to maintain the plant in health. The Rothamsted 

 experiments, however, served to show that nitrogenous 

 manures have little effect (indeed, sulphate of ammonia 

 may be harmful), but that mineral manures, and potash 

 in particular, are of great value. Nitrate of soda has 

 sometimes been found beneficial to st-'mu'ate a weakly 



