基于变化阶段特点的亚热带红壤硝化模式及其影响因素分析

在土壤最大持水量60%和温度30℃的实验室培养条件下,对采自江西的15个第三纪红砂岩母质发育的自然土壤（灌丛和林地）和农业利用土壤（茶园、旱地和水稻）进行了56 d实验室培养,研究了土壤NO3--N含量随时间的变化过程及阶段特点。结果显示,发生净硝化作用的14个土样NO3--N质量分数随时间的变化表现＂J＂型增长和＂S＂型增长2种模式。＂J＂型增长模式的6个土样,67%为自然土壤,其NO3--N质量分数增长具有15~35 d的延滞期,符合指数方程N=N0e kt（P〈0.001）,N0值与有效磷质量分数呈显著的指数关系（P〈0.05）。＂S＂型增长模式的8个土样,88%为农业利用土壤,NO3--N累积无明显延滞期,符合Logistic修正模型N=Np/（1＋e2.e-rt）（延滞期td=0,P〈0.001）,由模型获得的土样最大硝化速率vm与土壤全氮质量分数和全碳质量分数具有极显著的正相关关系（P〈0.001）,达到最大硝化速率所需的时间tm与风干土的NO3--N质量分数呈显著正相关（P〈0.05）。上述结果表明,农业利用措施,特别旱作种植可消除亚热带土壤硝化作用的延滞期,从而使铵态氮肥施入土壤后快速转化成为硝态氮,增大硝态氮淋失的风险。

Nitrification model of the time course characteristics of subtropical red soils and factor analysis

A total of 15 soils derived from tertiary red sandstone in Jiangxi Province,including the natural soils covered by the brush and forest and the agricultural soil covered by tea,upland crops,and flooded rice,were incubated at 30 ℃ with a soil moisture content of 60% water holding capacity（WHC） for 56 days.The characteristics of the time course of NO3——N accumulation were analyzed and the nitrification models were investigated.The results show that there are two types（J mode and S mode） of time courses for NO3——N net accumulation.Six soils,mainly natural soils（67%） were classified under ＂J＂ model with an obvious delay step for 15~35 days.The nitrification in these 6 soils followed the exponential model N=N0e kt（P0.001） and the values for N0 were significantly correlated exponentially with the available phosphorus content.Another 8 soils,mainly agricultural soils（88%） were classified under the ＂S＂ model with no delay step.The nitrification in these 8 soils followed the modified logistic model N=Np/（1＋e2？e-rt）（delay step is 0 d;P0.001）.The maximum nitrification rate（vm）,calculated using the model parameters,were significantly positively correlated with total nitrogen and total carbon contents（P0.001）,and the days reaching to the vm were correlated with initial NO3——N content（P0.05）.These results indicate that agricultural use,especially upland cropping,could eliminate the delay step of nitrification in the subtropical red soils,which would accelerate the transformation of NH4＋-N into NO3——N and then threaten the environment with a high risk of NO3——N leaching and runoff.