施氮量对植烟土壤不同土层无机氮质量含量的调控

为研究不同施氮量对土壤各层次和烤烟各生长期土壤中无机氮质量含量的影响,大田试验中设置5个氮肥施用量并分配在基肥、苗肥和追肥时期施用,烟苗移栽后第5周开始分7次钻取3个土层样,样品冷藏贮存并用流动注射分析仪测定硝态氮和铵态氮质量含量。结果表明：各施氮处理在移栽后第6周前0～20 cm土壤中硝态氮质量含量大于铵态氮,施用氮肥越多,土壤中无机氮质量含量提高幅度越大,施氮肥对0～20 cm土壤中无机氮质量含量的影响在烟株生育前期要远大于对20～40 cm土壤中无机氮质量含量的影响,同一时期不同深度比较,0～20 cm土层中硝态氮质量含量略大于20～40 cm和40～60 cm土层的硝态氮质量含量;烟株移栽7周后,0～20 cm土层中硝态氮被极大耗竭。各施氮量在各土层铵态氮质量含量变化幅度远大于硝态氮,铵态氮质量含量从第6周即开始上下波动,并在50 mg/kg附近上下变动,第8周土壤各层铵态氮质量含量有一个上升峰,而硝态氮质量含量在第7周停止快速下降后进入0～100 mg/kg范围的较平稳波动阶段。认为：不同施氮量对于生育前期和0～20 cm土层硝态氮质量含量影响深刻,但促进烤烟打顶前足量吸收并形成健壮烟株的合适施氮量还需结合烟草产量与品质而定;铵态氮调控是调节后期氮供应的关键。

Regulation of soil inorganic nitrogen by applying different nitrogen rate on flue-cured tobacco-planting soil

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 0-20 cm 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 0-20 cm depth was larger than that in 20-40 cm and 40-60 cm 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 50 mg/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 0-100 mg/kg.It was concluded that during earlier groth stages nitrogen fertilizer rates have profound impact on the inorganic nitrogen in layer of 0-20 cm,ammonium regulation is the critical measure for optimizing nitrogen supply in the later growth stage.