188 The Rothamsted Grass Experiments. 



part, lost by drainage ; and that, so far as it k not so, it 

 becomes so locked up, or distributed within the soil, that it 

 is at any rate very slowly, and, in some cases, perhaps 

 never fully recovered in subsequent crops. 



Secondly, the principle ignores the difference in the 

 character and capabilities of different soils. Take two 

 opposite cases : A light, porous, almost exclusively sandy 

 soil, which itself yields up little or nothing to growing 

 plants, but which may, nevertheless, produce good crops 

 under high farming, will probably suffer great loss of 

 manurial constituents by natural drainage; so that, if no 

 more were to be supplied than were removed, there must 

 obviously be a decline of fertility. Suppose, on the other 

 hand, a rich and deep loam, which would, under good 

 mechanical cultivation and drainage, supply annually a 

 considerable amount of potash, for example, to say nothing 

 of other constituents, for hundreds and perhaps for thousands 

 of years ; surely, in such a case, it is not necessary to supply 

 as much in manure as has been removed in the crops. 



Further, experience teaches that, in the actual condition 

 of our soils, and of agricultural practice, the exact compo- 

 sition of the crops we remove, or wish to grow, is no direct 

 guide to the description and the amount of manurial con- 

 stituents which will be most effective. Thus, an average 

 crop of wheat will remove even rather more phosphoric acid 

 than an average crop of barley; but experience teaches 

 that, in the case of land of the same description, and in the 

 same condition, superphosphate of lime is, as a rule, used 

 with very much more benefit to the spring-sown barley than 

 to the autumn-sown wheat. The wheat, being put in four 

 or five months earlier, has so much more time for root- 

 distribution, and acquires a greater capability for food 

 collection. The barley, on the other hand, depends very 

 much more upon the stores available within the surface 

 soil. Again, superphosphate is, in practice, of very special 

 benefit to the so-called " root crops," though the amount of 



