Symptoms of boron and calcium deficiencies are much alike. When calcium uptake is low, plants need less boron. When calcium use is high, boron deficiencies develop more rapidly. The two chemicals should be in a certain ratio to work well together-eighty parts calcium to one part of boron as maximum and 600 parts calcium to one of boron as a minimum. There is also evidence of a relationship between boron and potash, but the exact nature of this has not been clarified.
The addition of organic matter to soil releases boron that has been locked up in an insoluble form and makes it available to plants. Soil moisture also affects boron availability. As long as the soil is moist, boron remains soluble but in dry soil it reverts to an insoluble form.
Boron is credited with affecting fifteen different functions in plant growth. Certainly it is a mighty midget of an element.
Copper is both a poison and a nutrient. One of the earlier chemical weed killers was copper sulfate. The famed Bordeaux mixture, perhaps the first chemical fungicide, is a copper material that is used to destroy a fungus, which is, of course, a form of plant life.
The fact that copper is a nutrient was not proved until 1927. About that time, lack of copper was proved to be the cause of a slow decline in vigor of citrus trees. Its lack seems to affect many func-
tions of plant growth, yet its role has not as yet been well defined. Two places where it may be in short supply are in mucks and in sandy soils of Florida. One way to test whether copper is needed is to spray plants with a weak solution of Bordeaux mixture. If copper is lacking, a marked improvement in foliage color and vigor will be evident in a week. For soil treatment, an application of 10 pounds of copper sulfate per acre is recommended.
Many obscure and puzzling diseases have been traced to manganese deficiency without too many clues as to how this affects plants. Recently, chlorophyll research with radioactive isotopes has shown why the lack of manganese causes so much trouble. Along with iron, it is vital in chlorophyll formation and, if it is missing, production of starches and sugars is severely checked.
In most cases, manganese deficiency alters the color of foliage in some way. When leaf veins remain a dark green but areas between veins turn yellow or brown and finally break up, you can suspect a lack of manganese. It is seldom toxic when present in excess but in tobacco fields in Kentucky and Connecticut signs of poisoning have been noted. Again, leaf color is affected, with severe chlorosis and yellowing of the foliage.