Novel slow-releasing micronutrient fertilizers .2. Copper compounds

The development of a new type of slow-releasing copper fertilizer which is based on a short-chain polyphosphate structure, is described. Kinetics of polymerization of cupric phosphate at various Cu:P ratios and temperatures were studied, and the products were characterized. The desired fertilizers were formulated by selecting the appropriate copper polyphosphates and then neutralizing them to improve their properties. The fertilizers were analyzed by chemical methods, IR, XRD, solubility studies, and plant growth experiments. They were observed to have short-chain P-O-P linkages and contain amorphous as well as crystalline phases. Their water solubility was <5%, but in organic complexants, like citric acid or diethylenetriaminepentaacetic acid, solubilities were >90%, thereby indicating excellent plant availability. Plant growth experiments showed that copper calcium polyphosphate is an efficient source of copper, comparable to CuSO4; however, lower dosages are required with the former than with the latter.