Effects of Planting Dates and Nitrogen Fertilizer Application on Growth and Yield of Contrasting Genotypes of Maize (Zea Mays L.)I: Leaf Growth and Its Relationship with Grain Yield

Field experiments were conducted at the University of Ilorin Teaching and Research Farm, Bolorunduro, to evaluate the effects of different levels of N application on leaf growth and its relationship with grain yield of contrasting maize genotypes planted at three planting dates. Leaf extension growth at three leaf insertions (nodes 4, 8, and12) was measured from emergence until two consecutive measurements were the same. Thereafter, leaf growth parameters including leaf extension rate, leaf extension duration and final leaf length were calculated by fitting a linear regression of leaf length against time (days after planting DAP). Leaf area index was also calculated at weekly intervals from 21 to 63 DAP. Increasing N application increased leaf extension rate (LER) in both genotypes and at all planting dates, but had no significant effect on leaf extension duration (LED). These results indicate that LER was the most important factor influencing the final leaf area production. Leaf area index was consistently higher with maize planted in May and least with those planted in June. Positive relationships were obtained between grain yield, LER and final leaf area (FLA), while LED showed inverse relationship with grain yield. These results suggested that N application increased grain yield through improved leaf area production resulting from faster LER and shorter LED. The determination of the contribution of leaf growth parameters to grain yield through regression analyses showed that the combined effects of LER, LED, and FLA made significant contribution to grain yield ranging from 33.3%with June planting to 53.4% with July planting. The results further showed that the combined effects of the leaf growth parameters were similar for both the hybrids (R2=47.5%) maize genotypes. Overall, application of 90kg N/ha gave the best leaf area production and hence the highest grain yield thereby indicating the rate to be the optimum for maize production in the study area. JARD Vol. 3 2004: pp. 83-98