Response of Maize (Zea mays L.) to Deficit Irrigation Combined with Reduced Nitrogen Rate is Genotype Dependent

Deficit irrigation and low nitrogen (N) fertilization rate cause negative effects on maize grain productivity; such effects differ from genotype to genotype. The main objectives of the present investigation were to: (i) identify the drought and low N tolerant genotypes, (ii) estimate the superiority of tolerant to sensitive genotypes and (iii) assess the differential response of maize genotypes to elevated levels of nitrogen. Maize genotypes were evaluated in 2016 and 2017 seasons under three N rates: high; 285.6, medium; 166.6 and low; 47.6 kg N/ha and two irrigation regimes: well-watered (WW) and water stressed (WS) at flowering. A split-split-plot design with three replications was used. Main plots were allotted to irrigation regimes, sub-plots to N rates and sub-sub-plots to genotypes. The tolerant (T) and sensitive (S) genotypes were identified under each stress. Grain yield/plant (GYPP) of T genotypes was significantly (P≤ 0.01) superior to as compared to S genotypes by 109.5%, 39.6% and 141.9% under Low-N, drought, and drought combined with low-N, respectively. Superiority of T over S genotypes in GYPP was associated with significant (P≤ 0.01) superiority in ears/plant (11.5, 13.15 and 11.99%), 100-kernel weight (38.65, 30.46 and 30.99%), kernels/row (22.81, 11.28 and 20.07%), Nitrogen use efficiency (109.49, 39.62 and 141.89%) and shortening in anthesis-silking interval (-44.56, -29.58 and -29.08%), under the three environments, respectively. A significant linear response on elevated levels of nitrogen was shown by 13 genotypes, but a quadratic response was shown by six genotypes. The present study suggested that further investigation should be conducted to identify the optimum N fertilization rate for each newly developed variety of maize.