NOVEL SLOW-RELEASING MICRONUTRIENT FERTILIZERS .2. COPPER-COMPOUNDS

The development of a new type of slow-releasing copper fertilizer whic h is based on a short-chain polyphosphate structure, is described. Kin etics of polymerization of cupric phosphate at various Cu:P ratios and temperatures were studied, and the products were characterized. The d esired 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, solubili ty studies, and plant growth experiments. They were observed to have s hort-chain P-O-P linkages and contain amorphous as well as crystalline phases. Their water solubility was <5%, but in organic complexants, l ike citric acid or diethylenetriaminepentaacetic acid, solubilities we re >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 requ ired with the former than with the latter.