Overliming is often a cause of a shortage of manganese since this element readily locks up (becomes insoluble) in alkaline soils. Formerly the addition of sulfur was recommended when manganese deficiencies were suspected. This worked only if manganese was present originally and had locked up because of too high a pH. Thus when this element seems to be needed, lowering the pH to about 6.0 by the addition of sulfur is recommended. The manganese itself is supplied by applying 10 pounds of manganese sulfate per acre, or four ounces to 1,000 square feet of garden area. If the soil is already acid, 3 to 5 pounds of manganese sulfate per acre should be enough.
Although needed in fantastically small amounts (an ounce will supply enough to fertilize an acre for several years!), molybdenum is being recognized more and more as a vital micro-nutrient. Its most
important function is to help certain free-living bacteria to fix nitrogen directly from the atmosphere, without the need for growing a crop of legumes. True, this molybdenum action is hardly a major source of nitrogen, but moly (as it is called for short) is needed for other purposes anyhow. If a soil contains none of it, clovers, tomatoes, certain fruit trees and a number of other plants will not grow. The amount needed is one part in 100,000,000 parts of soil, yet this barely-detectable bit of molybdenum is critical.
Unlike many other metallic elements, moly is released by liming. Normally, soils which are limed regularly are not deficient in molybdenum.
At various times in recent years, other elements have been studied in relation to plant nutrition but the need for them is not well established. Cobalt, for example, is taken up by plants but plants grow well without it. It is, however, essential to animal growth and lack of it in forage plants causes serious deficiency diseases in cattle. These ailments go by such names as salt-sickness, bush-sickness, pining, pine, vinkish and dasing (the last four are English dialect names) and marasmus (in Australia).
Certain plants need some chlorine to grow but this element is so often present in fertilizers, table wastes or organic matter that it is never deficient in garden soils. Iodine and fluorine have not been proved essential, although they are absorbed by most plants.