秸秆在土壤内分解初期氮素矿化与固持的模拟测定

Simulation of nitrogen mineralization and immobilization of crop straw during its initial decomposition in soil.

利用模拟软件Modelmaker对3种作物秸秆在土壤内分解初期氮素循环转化过程进行了模拟,取得了土壤铵态氮、硝态氮、微生物氮及其15N丰度等6个变量模拟值和测定值的良好一致性.模型模拟对氮转化速率测定的结果表明,土壤微生物主要固持铵态氮,对硝态氮固持非常微弱.氮矿化主要发生于作物秸秆,腐殖质氮的矿化极其微弱.一级动力学方程对秸秆氮素矿化过程的描述优于零级动力学方程.微生物固持氮的再矿化过程落后于氮固持过程,假定再矿化不发生或认为再矿化与固持化同时进行可导致氮矿化与固持速率测定的严重误差.忽略氮硝化过程和挥发损失将导致氮矿化和固持速率的测定值偏低.净固持或净矿化的产生不仅与秸秆碳氮比有关,而且与秸秆在土壤内分解时间有关.

The nitrogen (N) transformation of crop straw during its initial decomposition in soil was simulated by Modelmaker software.A good fit was obtained between the simulated and measured data of 6 variables,including the amount of soil ammonium N,nitrate N,microbial biomass N and their ~ ~15 N atom %.The simulation results indicated that the main N form immobilized by soil microbes was ammonium,while the immobilization of nitrate was very small.N mineralization occurred dominantly in crop straw but very small in humus.The N mineralization of crop straw could be better described by first order than zero order kinetics.N re-mineralization occurred later than N immobilization.The assumptions on the absence of N re-mineralization or the simultaneous presence of re-mineralization and immobilization during straw decomposition led to a serious error in calculating the gross N mineralization and immobilization; while no consideration of nitrification and volatilization losses led to a low estimation of gross N mineralization.The occurrence of net N mineralization or net N immobilization depended not only on the C/N of straw,but also on the duration of straw decomposition.