稻田土壤硝化作用是陆地氮循环的重要组分之一，也是影响着水稻氮吸收的潜在途径。耕作通过改变土壤底物浓度与通气性，影响硝化微生物与硝化作用，然而作物的生长往往掩盖与混淆了耕作对其的影响。同时，当前研究较少从“土壤—微生物—作物”角度探讨免耕稻田土壤硝化作用、硝化微生物与水稻氮吸收的内在关系。为此，本项目拟以创建5年的常规翻耕、平作免耕与厢作免耕稻田为研究对象，利用定量—聚合酶链式反应方法、聚合酶链式反应—变性梯度凝胶电泳法等研究硝化功能微生物（氨氧化细菌AOA、氨氧化古菌AOB）的丰度与结构的动态变化特征，探明其对硝化作用的相对贡献；通过大田多时段采样分析，研究稻田土壤硝化作用的动态变化规律；结合水稻氮吸收模型与结构方程模型，探明免耕稻田硝化作用、功能微生物与水稻氮吸收的关联机制，揭示硝化作用对水稻氮吸收的影响。本项目旨在为免耕稻田合理施用氮肥与推广免耕技术提供科学依据。

Nitrification in paddy soil is one of important components of terrestrial nitrogen cycling, which affects nitrogen uptake by rice. Tillage practices affect soil nitrifying microorganism and nitrification through altering soil carbon/nitrogen substrate and permeability. However, the crop growth masks generally the tillage effects on nitrifying microorganism and nitrification. In addition, relative few studies investigated relationships among nitrification, nitrifying microorganisms and rice nitrogen uptake under no-tillage based on the soil-microorganism-crop system. Therefore, a field experiment established 5 years ago will be conducted to study the effects of different tillage modes (conventional tillage, conventional no-tillage, and no-tillage with wide ridge) on nitrifying microorganism and nitrification in central China. Using RT-PCR and PCR-DGGE methods, our objective is to assess seasonal changes in AOA and AOB abundance and structure under different tillage modes, and also to estimate contributions of AOA and AOB to soil nitrification. Moreover, the study will discuss the seasonal changes in soil NH4+ content, NO3- content, and nitrification as affected by tillage modes. Furthermore, the study will reveal the relationships among nitrification, nitrifying microorganism and rice nitrogen uptake under different tillage modes by Structure Equation Modeling and Rice Nitrogen Uptake Modeling. Therefore, the study will provide a scientific basis on how to apply nitrogen fertilizer in rice field to develop sustainable rice production.