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| Regulation of soil inorganic nitrogen by applying different nitrogen rate on flue-cured tobacco-planting soil |
| （1.College of Resources and Environmental Science, Henan Agricultural University，450002, Zhengzhou; 2.Enshi Autonomous Prefecture Tobacco Company,Hubei Province，445000，Enshi，Hubei：China） |
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Abstract Different nitrogen fertilizer rate were applied in the flue-cured tobacco planting soil to evaluate the nitrogen dynamic in different soil layers at different growth stages. In field trial nitrogen fertilizer with 5 different rates were applied to soil at 3 stages before and after transplanting. Soil were sampled at 3 layers for 7 times during tobacco growth, and the soil sample were stored under refrigeration and then analyzed with flow injection analyzer. The results are as follows: the nitrate nitrogen(NO-3-N) content within the upper 0-20cm was larger than the content of ammonium nitrogen(NH+4-N) since 6th weeks before the transplanting of flue cured tobacco and the more the nitrogen fertilizer applied, the higher inorganic nitrogen content was. The effect of nitrogen fertilizer on the inorganic nitrogen content in 0-20cm depth was larger than that in 20-40cm and 40-60cm depth. The nitrate decreased dramatically since 7th weeks after transplanting. The varied range of ammonium was much bigger than that of nitrate, ammonium begin to fluctuate from 6th week after transplanting and waved around about 50mg/kg for all applied nitrogen rates and in all soil layers, and a peak of ammonium content occured in 8th week in all soil layers. The decrease of NO3-N content stopped in 7th week, and then entered into a stage of smoothly fluctuation in the range of 0-100mg/kg. It was concluded that during earlier groth stages nitrogen fertilizer rates have profound impact on the inorganic nitrogen in layer of 0-20cm, ammonium regulation is the critical measure for optimizing nitrogen supply in the later growth stage.
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Received: 21 May 2012
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