Optimal ratio of nitrogen basal application and top-dressing for N uptake, distribution and yield of sesame

Objectives The study aimed to ascertain the appropriate application ratio of nitrogen in basal and topdressing to achieve high sesame yield and quality, high fertilizer use efficiency, and low soil N residue.

Methods A pot experiment using the ¹⁵N-tracer technique was conducted with white sesame cultivar of ‘Zhengtaizhi 1’ as tested material. At the base of same N application rate of 0.9 g ¹⁵N-labeled urea per pot, the N was applied in ratio of basal to topdressing (at the initial flowering stage) of 1∶0 (N_1∶0), 2∶1 (N_2∶1), 1∶2 (N_1∶2), and 0∶1 (N_0∶1). The N uptake, distribution and yield of sesame were examined.

Results Among the four treatments, N_2∶1 had the highest single plant yield, followed by N_1∶2, and the yield difference with both N_1∶0 and N_0∶1 reached a significant level. The total uptake of nitrogen per plant at the initial flowering stage decreased with the decrease of ratio of basal fertilizer, the uptake of N per plant was the highest in N_2∶1 treatment and the lowest in N_0∶1 treatment. The N uptake from fertilizer by sesame at the initial flowering period was in order of N_1∶0 > N_2∶1 > N_1∶2, and that from soil was the highest in N_2∶1 treatment. The distribution of N both from soil and fertilizer was in order of leaves > stems > root at the initial flowering period. At maturity, the largest single plant biomass, the highest seed N uptake and total plant N uptake were obtained in N_2∶1 treatment, while the lowest in N_1∶0 treatment, with a significant difference in the items between N_1∶0 and N_2∶1 treatments. The proportion of fertilizer N uptake by plant was 23.7%−29.1%, that of soil N was 70.9%−76.3%. The N uptake from both fertilizer and soil was in order of seeds > leaves > stems > capsule > root, and the seed N uptake was significantly higher than others and accounting for 33.0%−44.3% of total plant N uptake. The fertilizer N utilization rate of the four treatments was in range of 17.8%−32.5%. The fertilizer N utilization rate in N_2∶1 treatment was significantly higher than that in N_1∶0, and the difference among the N_2∶1, N_1∶2, and N_0∶1 was not significant. The recovery rate of ¹⁵N in different treatments varied significantly from 16.2% in N_2∶1 to 31.3% in N_0∶1 at harvest.

Conclusions Under the experimental condition, applying nitrogen fertilizer in ratio of basal to topdressing of 2∶1 could produce the highest sesame yield and fertilizer nitrogen use efficiency, and leave less in soil, so is thought to be optimal nitrogen application strategy.