PRINCIPLES OF MANURING 123 



deciding whether to use nitrate of soda or 

 sulphate of ammonia, he cannot do better 

 than apply both, either separately or in 

 mixture. Field experiments have shown 

 conclusively that on the average of soils and 

 seasons one will usually get a larger crop 

 by applying half dressings of both nitrate of 

 soda and sulphate of ammonia to the same 

 area of land, than by using only one or other 

 of these two substances. The gain in yield 

 may not be striking, but, in the case of the 

 turnip crop, for instance, it may amount 

 to as much as a ton per acre, and the value 

 k of this weight of roots is much more than 

 sufficient to compensate for the extra labour 

 of mixing the two manurial substances. 

 Sometimes, indeed, the crop given by the 

 mixture will be greater than the crops 

 grown by either of the two substances used 

 alone. The reason of the superior action 

 of the mixture would appear to be that it 

 furnishes two kinds of nitrogen, one of which 

 acts quickly, and the other more slowly. 

 The former, therefore, nourishes the crop in the 

 early part of the season, while the latter 

 becomes operative somewhat later, at a 

 time, namely, when the effects of the other 

 are on the wane. 



Of late years considerable attention has 



