largely of quartz-silicon dioxid--are very deficient in potassium;
consequently the experiments or demonstrations conducted by the
potash syndicate at Southern Pines, North Carolina, show very marked
increases from the use of potassium salts on such soil, although the
result ought not to be used to encourage the use of such fertilizers
on normal soils, which are exceedingly rich in potassium.

Even in soils abundantly supplied with potassium temporary use may
well be made of soluble potassium salts when no adequate supply of
decaying organic matter can be provided. For this purpose,
kainit--which contains potassium and also magnesium and sodium in
chlorids and sulfates--is preferred to the more concentrated and
more expensive potassium salts. About 600 pounds an acre every four
years is a good application. The kainit will not only furnish
soluble potassium and magnesium but will also help to dissolve and
thus make available other mineral plant food naturally present or
supplied, such as natural phosphates. When the supply of organic
matter produced in crops and returned either in farm manure or in
crop residues becomes sufficiently abundant, then the addition of
kainit may be discontinued on normal soil.

Thus, as an average of 112 separate tests covering four different
years, on the Southern Illinois experiment field on worn, thin land,
at Fairfield, the use of 600 pounds an acre of kainit once in four
years increased the yield of corn by 10.7 bushels where no organic
manure was used, and by only 1.7 bushels when applied with eight
tons of farm manure.

Liming the Soil