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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