THE WHEAT CROP. 89 



We thus see what we have to return to the soil as a 

 compensation for the mineral substances which a crop of 

 wheat takes from it. Now, of the mineral constituents 

 given in the analyses there are but two which we need 

 concern ourselves about the potash and the phosphoric 

 acid as all soils suitable for cultivation may be said to 

 contain the others in sufficient abundance. These two 

 then ought to be supplied either at once to the soil, in the 

 shape of a special manure, or by manuring through the 

 agency of other crops in the course of the rotation. M. 

 "Way in his investigations gives 31*37 as the average per- 

 centage of potash, and 45* as the average proportion ot 

 phosphoric acid in the grain of wheat, and suggests that 

 the mineral constituents of an average crop of wheat may 

 be returned to the soil by a mixture of the following 

 composition. 1 



84 Ibs 

 20 



4 



8 



1 



23 



H 



of Silica (as a soluble salt). 

 Phosphoric acid. 

 Sulphuric acid. 

 Lime. 

 Magnesia. 

 Peroxide of Iron. 

 Potash. 

 Soda. 



These mineral (inorganic) substances form, as is shown, 

 but a small portion of the grain, the bulk being composed 

 of water and what are termed proximate organic com- 

 pounds. In wheat in good condition the average pro- 

 portion of water is about 1 2 per cent., 2 and the proportion 

 of bran may be taken at from 10 to 12 per cent. also. 

 These two constituents furnish but little alimentary 

 matter to the consumers. The other ingredients, consist- 

 ing principally of starch and gluten, with small propor- 



1 Roy. Agri. Soc. Jour., vol. vii. p. 676. 



2 The saiue quantity is found in both the straw and the chaff. 



