Interactive effects of plant growth regulators and nitrogen on corn growth and nitrogen use efficiency

Our objective was to determine the combined effect of some plant growth regulators and nitrogen (N) on corn growth, yield and nitrogen use efficiency. A potted experiment was conducted with two levels of growth regulators [i.e. with or without treatment with Seed king (Kinetine), Root king (Indole-butyric acid) and More king (Chitosan)], two maize cultivars (Calabar White and Obatanpa-98 and three nitrogen rates (0, 90 and 180 kg/ha in the form of urea). The measured parameters were growth attributes, nitrogen uptake, dry matter yield, harvest-index, shoot to root ratio, yield attributes and agronomic and physiological nitrogen use efficiency. Calabar White had taller plants (154.53 cm) more leaves (12.00) and larger leaf area (466.98 cm2) than obatanpa-98 at 6 weeks after sowing. The dry matter yield of both leaf and stem increased significantly (P ≤ 0.05) with increasing N rates but the growth regulators significantly (P ≤ 0.05) increased only the leaf dry matter. The interaction between growth regulators and nitrogen significantly affected the leaf dry matter but not the stem dry matter. There was a considerable (P ≤ 0.05) increase in harvest-index (HI) at the 90 kg/ha N rate with growth regulators and Obatanpa-98 had better HI (30.81%) than Calabar White (27.41%). Obatanpa 98 also had much (P ≤ 0.05) higher grain yield (87.42 g/plant) than Calabar White (65.40 g/plant) but for both cultivars, the grain yield increased progressively with increasing N rate. The uptake of N differed significantly (P ≤ 0.05) among the different partitions of maize (leaves, stems and grains) at various growth stages. Calabar White had the highest N uptake in the leaves and stem whether at silking or at harvest. Obatanpa-98 partitioned more N to the grains than Calabar White. Agronomic nitrogen use efficiency (ANUE) was highest (21.31 gg−1) at the 90 kg/ha N rate with Obatanpa-98 having a superior (20.26 gg−1) ANUE to Calabar White (15.94 gg−1). The physiological nitrogen use efficiency (PNUE) was also highest (8.14 g/kg) at the 90 kg/ha N rate with Obatanpa-98 being more efficient (8.08 gkg) than Calabar White (6.26 g/kg). Thus, both cultivars treated with 90 kgN/ha with or without growth regulators would best optimize nitrogen fertilizer use. However, the growth regulators increased the yield of Calabar White significantly only when no N was applied. In contrast, they increased the yield of the hybrid Obatanpa-98 at all N rates especially at the 180 kgN/ha rate. Thus, under the low input cropping common with Calabar White, treatment with the growth regulators would boost yield. A combined treatment of 180 kg N/ha with the growth regulators would ensure the best yield of Obatanpa-98.