CHAPTER VI 



VARIATIONS IN THE CHEMICAL COMPOSITION OF 

 FEEDING STUFFS 



WE have seen that plants manufacture more or less complex 

 organic substances and ash materials from carbon-dioxide, water, 

 and mineral components,, and that the energy thus stored up in the 

 plants is utilized by the animals feeding on these materials. Differ- 

 ent plants vary considerably in the amount of energy that they 

 supply, and the same plants vary according to their stage of growth 

 and other conditions. The main factors that influence the chemical 

 composition of plants will be considered in the following pages. 



The soil is an important factor in determining the quality as 

 well as the yield of the crops grown ; in a fertile soil, plants reach 

 their highest development, and maximum crops are secured. It 

 is possible to modify appreciably the percentage of different plant 

 constituents by special fertilization; an increase in the protein 

 content, e.g., may be secured by applications of a general fertilizer 

 that is high in nitrogen. By increasing the nitrogen content of the 

 soil in this manner the percentage of protein in barley was increased 

 from 13.77 to over 19 per cent. German scientists found the protein 

 content of wheat grown on different kinds of soil as follows: On 

 unfertilized soil, 16.25 per cent ; fertilized with nitrogen, 21.43 per 

 cent, and fertilized with nitrogen and phosphoric acid, 22.37 

 per cent. Differences are likely to occur in the composition of the 

 whole plant as well as, to a smaller extent, in the kernels, and it is 

 therefore as important for the stockman as for the general farmer 

 to adopt a good system of crop rotation that will secure the best 

 possible growing conditions for the different crops. Plants grown 

 in a soil rich in lime or phosphoric acid will contain a higher per- 

 centage of these constituents than those grown in a poor soil, and 

 will, therefore, be of superior value for feeding milk-producing 

 and growing animals, which require a liberal supply of these mineral 

 constituents. 



Climatic Environment. It would be wrong to assume, how- 

 ever, that the soil exerts the chief influence in determining the 

 physical properties or the chemical composition of a crop. In a 

 study of the influence of environment on wheat, which was continued 



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