Abstract

Effects of annual spraying of copper (Cu) fungicide by cocoa farmers in Nigeria needs immediate investigation to avoid copper toxicity which will affect uptake of other essential nutrients for plant growth. Laboratory and Screenhouse studies were carried out to investigate the effects of Cu application on availability of P, Zn, Fe and growth of maize. In the laboratory, copper was applied as CuSO₄ at 0, 10, 20, 30, 40 and 50 mg Cu kg^-1 to 100 g soil and left for 5 weeks for equilibration while in the Screenhouse, the same rate of Cu was thoroughly mixed with 1 kg soil in a plastic container. Maize was used as the test crop and growth parameters were monitored. Soil and tissue samples were analysed for Cu, P, Zn and Fe at the end of Laboratory and Screenhouse experiments. The experiment was arranged in a completely randomized design and replicated three times. Data obtained were subjected to analysis of variance; differences in means were tested using the Duncan Multiple Range Test. The results from Laboratory and Screenhouse experiments showed significant decrease in soil available P, Zn and Fe as rates of Cu increase over control experiment. The effect was more pronounced at application rate above 20 mg Cu kg^-1. Gradual decrease in maize plant height, stem girth, leaf areas index, P, Zn and Fe uptake were observed as rate of Cu application increased. For instant, at application rate of 10 and 20 mgkg^-1, available P uptake was 5.49 mg/pot and 3.08 mg/pot respectively. The negative impact of Cu accumulation on available P was consistent in all the experiments. The result of the experiment clearly revealed strong negative impact of excess Cu on availabilities and uptake of P, Zn and Fe in soil.

Key words: Copper, fungicides, application rate, Screenhouse, nutrients.