Nitrogen use efficiency and yield of corn (Zea mays L.) as affected by weed management and time of nitrogen fertilizer application.

Results of the study showed that weed control methods had no significant effects on all parameters studied except for leaf area index (LAI) and weed fresh weight at 50 DAP [days after planting]. Leaf area indices from W6 (handweeding four times) and W5 (preemergence application of atrazine and pendimethalin + hilling-up) were significantly higher than W1 (offbarring + hilling-up) and W2 (hoeing + hilling-up). W6 gave the most effective control of weeds based on fresh weed weight at 50 DAP. W2 and W5 provided poor control of weeds. W1 and W4 (preemergence application of pendimethalin + spot hoeing + hilling-up) provided less satisfactory control of weeds than W6 but better control than W3 (preemergence application of atrazine + spot hoeing + hilling-up). The differences in crop LAI and weed control efficacies were not reflected in grain yield and nitrogen use efficiency of the crop indicating that all the six weed control methods provided adequate control of weeds in the trial site. The time of N fertilizer application efficiency affected early crop growth and vigor, days to tasseling and silking, plant and ear height, leaf area index, total dry matter yield, ear kernel filling length, number of kernel rows per ear, number of kernels per ear, total N uptake, efficiency of N absorption, and utilization for grain production of corn. Early application of N fertilizers (F1, F3, F4) gave taller, greener, and more vigorous crops while delayed N fertilizer (F2) produced nitrogen deficient plants. Days to tasseling and silking were shortened with application of higher rates of N at early stages (F1, F3) but were delayed when N fertilization was done later (F2) and when lower rate of N was used (F4). Plant and ear height were increased with high and early split application of N (F1). Higher LAI was obtained with high and early split application of N (F1, F3) but delayed N fertilization (F2) and split application of small amounts (F4) gave lower LAI of corn. Total dry matter yield from F2 was higher than other treatments.