Nitrogen Use Efficiency of Early Open-Pollinated Maize Varieties and their F1 Hybrids for Tolerance to Low Soil Nitrogen Stress

In the tropical savanna of Africa where low soil nitrogen (N) is a major constraint to maize production, the development of early maturing maize tolerance to low-N and drought is very essential. Field trials were conducted at the Lower Niger River Basin Development Authority, Ilorin, Nigeria on a Typic Paleustalf soil to assess the response of ten early drought-tolerant open-pollinated varieties (OPVs) and their F 1 hybrids to low-N fertilizer conditions. The trials were set up in a split-plot arrangement with three N fertilizer levels (0, 45 and, 90 kg N ha −1 ) as the main plot and the genotypes as sub-plot. Each sub-plot within N level was four-row, laid out in a randomized complete block design of four replications. Planting was carried out on 22nd July, 2018 and 20th July, 2019. There were significant interactions between the genotypes and N level for all characters, with increased variation as the level of N decreased. The maize grain yield advantage was 1.72 t ha −1 and 1.95 t ha −1 for OPVs and hybrids, respectively; with applied 90 kg N ha −1 over no N. Nitrogen use efficiency (NUE) was optimum at 45 kg N ha −1 in all the genotypes. Grain yield and NUE correlated positively with all the traits measured except days to 50% silking. Kernel number was most severely reduced by N stress but had a positive and highly significant correlation with grain yield at all N-rates. The hybrids Dmr-Esr Y Cif 2 × Ak 95 Dmr-Esrw, Ev Dt-Y 2000 Str C0 × Ak 95 Dmr-Esrw, and Tze Comp 4 C2 × Tze Comp 3 C2 had superior grain yield and NUE. This suggests that selecting for tolerance to drought may simultaneously confer tolerance to low-N stress.