Study on the proper nitrogen application rate and the ratio of basal to dressing in radish

A field experiment was conducted to study the effect of nitrogen application rates and methods on the uptake and distribution of N by radish using 15N isotope tracing method. Three N rates (0, 60 and 120 kg/ha) and two application proportions of basal∶15 d after seeding∶30 d after seeding［50%∶20%∶30%(A) and 30%∶20%∶30%(B)］were designed with total of five treatments reordered as N0, N60A, N60B, N120A and N120B, respectively. The result showed that the nitrogen absorbed from fertilizer and soil by radish，the residual N amount in the soil were increased significantly，the absorption and utilization rate and soil residual rate were decreased as consequence, although the N loss rate still increased with the nitrogen application rate increased from 0 to 120 kg/ha. At the application rate of 120 kg/ha, the nitrogen absorption was 30.50 kg/ha from the fertilizer and 53.64 kg/ha from soil, and the residual N amount in soil was 14.88 kg/ha with the treatment of N120A, the N absorption was 35.56 kg/ha from fertilizer and 56.61 kg/ha from soil and the residual N amount in soil was 17.81 kg/ha with the treatment of N120B. The root yield for the treatments of N120A and N120B were 67.6 t/ha and 72.5 t/ha, respectively, 64.07% and 66.67% higher than those for treatment N60A and N60B. The highest nitrogen use efficiency was obtained in the treatment of N120B. Therefore, appropriate nitrogen application with increasing topdressing nitrogen ratio in later growth stage could increase root yield of radish and the nitrogen use efficiency. The recommended N application rate for radish in the studied area is N 120 kg/ha with application ratio of 30% for basal, 20% for 15 d after seeding and 50% for 30 d after seeding.