A dark, healthy green foliage indicates a good supply of nitrogen, while a pale yellowish green may indicate a need of nitrogen.
A well developed head of grain, seed pod or fruit indicates liberal supplies of phosphoric acid and potash.
THE SOIL
Soils that are poor in humus are generally in need of nitrogen.
Heavy soils are generally supplied with potash but lack phosphoric acid.
Sandy soils are apt to be poor in potash and nitrogen.
SYSTEM OF FARMING
A system of general or diversified farming embracing crop products and stock raising, requires much less artificial manuring than does a system which raises special crops or quick growing crops in rapid succession, as in the case of truck farming or market gardening.
TESTING THE SOIL
Every farmer should be more or less of an investigator and experimenter.