1163. Why are mixed soils favourable to vegetation?
Because they contain the elements of nutrition essential to the development of the vegetables, and the plants absorb from them those constituents which are necessary to their growth.
1164. Why do farmers sow different crops in rotation?
Because every plant takes something from the soil, and gives something back; but all kinds of plants do not absorb nor restore the elements in the same proportions. Therefore a succession of crops of one kind would soon impoverish the soil; but a succession of crops of different kinds will compensate the soil, in some degree, for the nourishment withdrawn.
"He watereth the hills from his chambers; the earth is satisfied with the fruit of thy works."—Psalm civ.
1165. Why do farmers manure their lands?
Because, as soils vary, and crops impoverish the soils, the farmer employs manure to restore fertility, and to adapt the soils to the wants of the plants he desires to cultivate.
It is remarkable that Nature herself points out to man the necessity for changing the succession of vegetable growths.