Evaluation of Maize (Zea mays L.) genetypes for nitrogen use efficiency

Low soil Nitrogen (N) challenges of accessibility and high cost of N fertilisers in Zambia are the major constraints associated with maize production. Increased production can only be attained by the application of N fertilisers and by the use of improved germplasm with the ability to efficiently use applied N. Nitrogen Use Efficiency (NUE) technology has been used and remains a potential means of addressing some of the challenges associated with low available N in agricultural soils and the non-availability of inorganic nitrogen fertilisers to farmers. A study was carried at the National Irrigation Research Station, Nanga to evaluate and screen maize genotypes for NUE. To achieve this, the following were determined, NUE, N partitioning and secondary traits associated with low N tolerance. The experiment had two levels of N at 0 and 100 kg N ha-1 and was arranged in a Randomised Complete Block Design (RCBD). Nitrogen utilization efficiency, N uptake efficiency, N grain accumulation, N harvest index, harvest index, N uptake, grain yield and biomass yield varied significantly among genotypes at p < 0.001. The ranges for total grain N ha-1, harvest index, N harvest index, and biomass and grain yields were 28.9 - 235 kg ha-1, 0.2 - 0.45, 0.3 - 0.7, 5.7 - 27 tons ha-1and 1.4 - 9 tons ha-1, respectively. The NUE Partial Factor Productivity and NUE-AE exhibited significant differences at p < 0.001 and values ranged from 13 - 94 and 9.7 - 48.5 kg ha-1, respectively for all genotypes. Anthesis silking interval ranged from 0 to 5 days. Earliest genotype was L 857 and the latest were 151 and 152. The evaluation of NUE showed differences among the 30 genotypes. The results of this study show that among the 30 genotypes evaluated, 6 lines (658, 2035, 2026, 2006, 2091 and L 727) produced NUE-AE values higher than the reference genotype and the recorded world average, of 14.8 and 33 kg grain per kg N, respectively. For each kg of N applied these genotypes produced more grain than the rest of the genotypes. The genotypes that partitioned more of the vegetative N to the grain included 917, 2091, 652, 1061, 650, 658 and 2026. Based on the correlation analysis, genotypes with higher N utilisation efficiency partitioned more N to the grain. Overall, the NUE was determined mainly by the individual genotype and its interaction with the soil and environmental conditions. Secondary traits such as delayed senescence (stay green) N uptake, N uptake efficiency and grain N accumulation contributed positively to NUE. Based on the NUE-AE, the genotypes 658, 2035, 2026, 2006, 2091 and L 727 can be included in the next stage of the breeding programmes that have the objectives of breeding for tolerance to low N.