Nitrogen Use Efficiency of Quality Protein Maize (Zea mays L.) Genotypes

Use of more nutrient-use efficient Quality Protein Maize (QPM) varieties will likely play a pivotal role in maintaining or increasing crop yields and nutritional values in fields where soils are degraded. This study aimed to: (i) assess the nitrogen use efficiency (NUE) of different QPM inbred lines at various levels of nitrogen (N) fertilizer application; (ii) determine the relationships among NUE indices and yield; and (iii) determine the appropriate rate of fertilizer application for QPM genotypes under conditions of this study. Thirty-two QPM inbred lines were evaluated at 0, 30, 60, 90 and 120 kg N ha−1 N fertilizer application in a split-plot randomized complete block design with two replicates at the University of Fort Hare Crop Research farm, South Africa. Results revealed highly significant differences (p ≤ 0.001) for total nitrogen in biomass (Bio Total N), total nitrogen in grain (G Total N), grain yield, NUE and almost all the indices estimated across N levels. The top three genotypes which showed high-yielding potential at 30 kg N ha−1 include L2 (6.24 t/ha), L3 (6.47 t/ha) and L4 (6.34 t/ha), and were considered the most N-efficient genotypes under low N soils. The highest grain yields (6.74 t/ha) and highest NUtE (Nitrogen Utilization Efficiency) (1.93 kg grain/total N) were obtained at 90 kg N ha−1. Highly significant and positive correlation coefficients were found between NUE and yield (+0.9), NUE and NUtE (+0.9), NUE and HI (Harvest Index) (+0.5), NUtE and yield (+0.99), HI and yield (+0.5) and NUtE and HI (+0.5). Highest nitrogen uptake efficiency (NUpE) was obtained from the lowest fertilizer rate, which was 30 kg N ha−1.