Objectives Many factors affect cabbage yield and ammonia volatilization in rice–cabbage rotation system in purple soil. The research was aiming to clarify the trends of NH3 volatilization affected by nitrogen rates and climate factors, to give some recommendation for mitigating nitrogen loss in Sichuan Province.
Methods Field experiments were conducted with different nitrogen rates on cabbage in a purple soil. The nitrogen rate included N 0, 112.5, 150, 187.5, 225 and 300 kg/hm2. The N fertilizer was divided into two equal parts and applied for basal application and topdressing. A continual air-flow chamber method was used to measure the ammonia volatilization. The measurement was conducted successively for 14 days after basal fertilization or topdressing at 9:00–10:00 am and 16:00–17:00 pm till no ammonia volatilization was detected. The cabbage yield and nitrogen content in the cabbage were measured after maturity.
Results The total NH3 volatilization of the entire season increased from 2.27 kg/hm2 to 22.72 kg/hm2 with increasing nitrogen rate from 0 to 300 kg/hm2. When the nitrogen rate was increased from 0 to 150 kg/hm2, NH3 volatilization after basal fertilization was in range of 1.08–23.58 kg/hm2, greater than that after topdressing (0.21–2.83 kg/hm2), which was due to the higher temperature after basal fertilization than after topdressing. Cabbage yield increase became not significant when the N rate was over 187.5 kg/hm2, however, the total NH3 volatilization kept increased. The NH3 volatilization increase was not significant when the N rate was increased from 150 kg/hm2 to 187.5 kg/hm2, but became significant from 187.5 kg/hm2 to 225 kg/hm2 or 300 kg/hm2.
Conclusions Ammonia volatilization of cabbage occurs largely during the first two weeks after fertilization. Nitrogen rates and soil temperature are the two main factors affecting ammonia volatilization. Comprehensively considering the yield and N loss, the optimal total nitrogen rate is 187.5 kg/hm2.
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