MANURES FOR THE WHEAT CROP. 73 



with few exceptions, the worse the so-called " condition " 

 of the land, that is, the more it is in the agricultural sense 

 exhausted, the more striking would he the effect of exclu- 

 sively nitrogenous compared with that of exclusively min- 

 eral manures. 



" What, then, are the common practices of British agri- 

 cult are which lead to this result 1 



" Let us take an example as we have done "before the 

 practice of the so-called four-course rotation of roots, 

 barley, clover (or beans), and wheat. Let us further assume, 

 for the sake of argument, that on the average, 30 bushels 

 of wheat, 35 bushels of barley, and the meat from the con- 

 sumption of 10 tons of swedes and clover, equal to 6,000 Ibs. 

 of clover hay (or 1,500 Ibs. of bean corn), are the products 

 sold from each acre of the farm in the four years, and that 

 the straw of the corn crops, and the excrements from the 

 animals feeding on the roots and the clover or beans, are 

 retained on the farm as manure, and returned periodically 

 to the land. Confining attention, for the sake of simpli- 

 city of illustration, to those mineral constituents which, so 

 far as existing knowledge goes, are the most likely to be- 

 come relatively deficient in the majority of soils, it may be 

 estimated that, under such a course, the average annual loss 

 per acre by the sale of corn and meat would be, of potass 

 from 4^ to 5 Ibs., of phosphoric acid from 7 to 8 Ibs., and 

 of silica about 3 Ibs. 



" But all practical men will admit that the amounts of 

 produce here assumed to be exported from each acre, or 

 equivalent amounts in other forms, could only be so under 

 one of two conditions. Either the soil must be naturally 

 a very fertile one, or the produce must be kept up by means 

 of purchased cattle food, or artificial manures. In the case 

 of a soil so fertile as to have yielded, for any considerable 

 number of years, the average produce supposed, without 

 assistance from import, it may well be questioned whether 

 it, with its workable subsoil, would not be competent to 

 yield annually, by decomposition, the necessary amounts of 

 the mineral constituents mentioned ; and if of them, of 



