Fate of Urea Nitrogen Applied to Rape Grown on a Red Soil and Efficiency of Urea in Raising Rape Yield

摘要

Fate of urea nitrogen (N) applied to rape grown on a red soil was investigated by the ~(15)N mass balance technique, and efficiency of urea and effect of nutrients balance in raising rape yield were investigated in a field plot experiment. One hundredand thirty-eight kg N/ha, 86 kg N/ha as basal dressing and 52 kg N/ha as top dressing, was applied with baud application technique. The experiment was conducted in the southeast of China, near Yingtan City, Jianxi Province. Results from ~(15)N mass balance study showed that when urea was applied as basal dressing the plant recovery was 44.0% of the applied N for Treatment T (with application of N, P, K, B and lime). Plant recoveries were 38.0% — 40.5% for Treatments -K, -B, -lime and +RS (without application of K, B or lime as well as with additional rice straw compared with Treatment T), which were not significantly different from Treatment T. In contrast, plant recovery was only 5.1% for Treatment -P (without application of P), indicating that P was the factor limiting N uptake by rape. However, N remaining in 0—0.30 m soil was high up to 71.6% for Treatment -P, while the corresponding data were 33.0%-42.6% for the other treatments. The total recovery of applied N (including plant recovery and Nremaining in 0-0.60 m soil) was 91.5% for Treatment T when urea was applied as basal dressing, while almost all the applied N was recovered when urea was applied as top dressing. It was suggested that N loss was greatly controlled by using band application method in this experiment. Results from the field plot experiment showed that N supply capacity of this red soil was very low, and the efficiency of the applied N was quite high, 7.1 kg rape seed was increased by application of one kg N for TreatmentT. Nitrogen and phosphorus were the key factors limiting rape yield, and the yield was very low when neither of them was applied. The yield in Treatment -K was significantly lower than that in Treatment T, with the former accounting for 77% of the later.