Effects of Copper Sources on Wheat and Soybeans Grown on Organic Soils1

Abstract

AbstractOptimum rates for and the residual effects of several new copper fertilizer materials have not been determined. Because the copper in these sources is complexed, usually with an organic ligand, it has been implied that they are more effective than copper sulfate.The immediate and residual effectiveness of copper sulfate and several new chelated and/or complexed copper materials were compared to determine the optimum rate of application for each source. Field experiments were conducted on four acid, organic soils, each of which was severely deficient in copper. Wheat (Triticum aestivum L.) yields were increased with an increase in the rate applied to 2.8 kg Cu/ha at three locations and to 5.6 kg Cu/ha at the fourth. There was no difference in the nature of the response obtained among sources so all sources were considered equally effective when equivalent amounts of copper were used.Soybeans [Glycine max (L.) Merr.] were double‐cropped behind wheat to determine the residual effect of these sources. Grain yields showed the same patterns of response to copper sources as were obtained with wheat. Plant analyses also revealed the same effects of copper applications as were obtained with grain yields. Distinct symptoms of copper deficiency developed in the control and low copper treatments in both crops.