EFFECTS OF NITROGEN APPLICATION RATES USING TREATED WASTEWATERS, ON NITROGEN UPTAKE AND CROP YIELD BASED ON POT TRIALS WITH MAIZE AND SOYBEAN

Glasshouse experiments were conducted to evaluate the effects of wastewater nitrogen on soil-plant interactions, and thereby provide information for improving wastewater effluent irrigation practices. Various concentrations of treated effluent from a trickling filter wastewater treatment plant were applied under controlled conditions using soya bean (Glicine max (L.) merrill) and maize (Zea mays L.) as the test crops. Both crops responded well to effluent irrigation, but with important differences between them in terms of grain dry matter and nitrogen uptake. This response was influenced by the timing and the amount of effluent applied, with decreasing effluent applications early in the growing season stimulating nitrogen uptake from the soil. Recovery of the applied nitrogen was greater in maize than soya bean under full irrigation. In addition an improvement in nitrogen utilisation was observed when an effluent deficit in the vegetative stage was followed by full effluent irrigation applied during the reproductive period.