Effect of N Management on Root Yield and N Uptake of Radishes in Southern China

Efficient nitrogen (N) fertilizer management is crucial for ensuring the maximum economic yield and reducing the risk of environmental pollution. The objective of this study was to determine the effect of N fertilizer management on root yield and N uptake of radish in southern China by using N-15 isotope tracing. A 2-year field experiment was conducted with three N rates (0, 60, and 120 kg N/ha) and two different application proportions, viz, A [50% at basal, 20% at 15 days after seeding (DAS), 30% at 30 DAS] and B (30% at basal, 20% at 15 DAS, 50% at 30 DAS) for each N rate, which were expressed as N-0, N-60A., N-60B, N-120A, and N-120B, respectively. The results showed that root yields were significantly increased with N rates increasing from 0 to 120 kg N/ha. The root yields for N-120A and N-120B were 67.60 t.ha(-1) and 72.50 t.ha(-1) at harvest, 64.07% and 66.67% higher than those for the treatment of N-60A and N-60B, respectively. Mean radish recovery of N fertilizer ranged from 25.90% at N-120A to 32.60% at N-60B, and N fertilizer residual rate in the soil ranged from 11.50% at N-120A to 14.90% at N-60B. About 17.50% to 35.70% of total uptake of N-15 derived from basal fertilizer was absorbed at seeding stage. However, 61.87% to 80.18% of total uptake of N-15 derived from topdressing fertilizer absorbed at root expanding stage. Therefore, appropriate nitrogen application with increasing topdressing nitrogen amount could increase root yield of radish and the nitrogen recovery efficiency. Nitrogen fertilizer application recommended was 120 kg Wha with 30% for basal, 20% for 15 DAS and 50% for 30 DAS in this study.