MANURES FOR THE WHEAT CROP. 77 



that if there really is an annual liberation of mineral con- 

 stituents in available form for the growth of plants, at least 

 a portion of this may, -with propriety, be sold off the farm 

 for good and all. 



" The exact amount of annual loss of mineral constitu- 

 ents which any soil, with its workable subsoil, can per- 

 manently support without injury, cannot indeed be proved. 

 But such evidence as is at command goes to show, that, 

 under the conditions at present existing, the nature and 

 extent of the loss to which our soils are subject are such, 

 that the majority are deficient of available nitrogen rather 

 than of available mineral constituents, so far as the require- 

 ments for full crops of the cereal grains are concerned. 



" Insisting strongly then, as we have always done, upon 

 the absolute necessity of a full supply of available mineral 

 constituents within the soil, relatively to that of nitrogen, 

 we still believe that, in the actually existing conditions of 

 British agriculture, it is not they, but the available nitro- 

 gen, that is generally to be relatively deficient. 



" What then are the sources of available nitrogen, within 

 the soil, to which the farmer must look for the production 

 of good crops of wheat ? 



" In former papers in this Journal we have pointed out 

 that his chief means to this end was the adoption of a 

 suitable rotation of crops, alternating with his corn the so- 

 called 'green,' 'fallow,' or ' fodder ' crops, an important 

 office of which it is to collect from natural sources, or to 

 conserve on the farm in the form of manure, available 

 nitrogen for the increased growth of the saleable cereal 

 grains. We have further maintained that, as either by 

 bare fallow, or a rotation of crops, with the consumption 

 of the fallow crops and the retention of the straw on the 

 farm, the accumulation of available mineral constituents 

 will generally be in excess of the available nitrogen, it is 

 the amount of the latter rather than of the former, that 

 will be the measure of the increased produce obtained by 

 such means 



" Indeed, on many of our heavier soils, and even on 



