The Stimulating Effect of External Applications of Copper and Manganese on Certain Chlorotic Plants of the Florida Everglades Soils 1

The successful growth of agricultural crops on raw peat soils has been a di~cult problem for many dacades. This was one of the outstanding problems confronting the Florida Everglades Experiment Station immediately upon its establishment in 1923. At that time poor plant growth was rather general on the Experiment Station soils, as well as on other raw peat soils of the Everglades. The first indication of a corrective for this poor plant growth was obtained in the summer of 1925. This work was enlarged and published by Allison, et c~l (~),3 in ~ 927. The results show in a remarkable way the stimulating influence of copper and manganese sulfates on the peat soils of the Florida Everglades. The exact nature of the stimulating action of these chemicals was unknown. However, several hypotheses seemed plausible. The most important of these were as follows: (a) Fungicidal action harmful soil organisms, (b) specific effect of the chemicals on soil toxins, and (c) nutritive effect. Since field trials showed that 2o to 30 pounds Of copper sulfate (CuSO4.sH20) per acre produced normal plant growth, the assumption concerning the fungicidal action seemed to be untenable, particularly in a m_edium of as high absorptive capacity as the soil in question. The counteracting effect of the chemicals on soil toxins also seemed untenable in view of the fact that appreciable amounts of soil toxins could not be isolated. However, the nutritive effect appeared more or less plausible in the light of recent investigations (7, ~ ~) concerning the effect of copper, manganese, tc., on plant and animal life. On the assumption that a portion of all soluble soil constituents pass into the growing plant, the increased amount of copper or manganese in plants grown on soils treated with these elements over that contained in plants grown on non-treated soils would not