紫色土发育过程中氮转化过程演变规律研究

Purple soil is widely distributed in the hilly areas of southern China, and it is notably concentrated in the Sichuan Basin. Purple soil is non-zonality soil with week capacity to maintain inorganic nitrogen. Great attention has been paid to nitrogen loss and its associated environmental effect of purple soil, as well as methods to increase N use efficacy of purple soil. However, few of them investigated the mechanisms of N transformation in purple soils and its relationship with the nitrogen loss. Land-using type changed both the development rates and N transformation process of purple soil. The project will measure N gross transformation rates in the purple soils in Sichuan by combined using the paired 15N labelling method and 15N tracing model, to investigate the relationship between land-using approach (forest、dry-land、rice-paddy) and the changes of soil N transformation mechanisms, and the relationships between soil N transformation and inorganic N form, fate, the transferred N form in purple soil of different developing stage. The research would be helpful to elucidate the mechanisms of the temporal-spatial variability in N transformation process of purple soil, to understand the influence of land-using approach on N transformation process of purple soil, and provide basic knowledge for N fertilization of purple soil.

紫色土广泛分布于我国南方地区，特别是四川盆地。紫色土是一种非地带性土壤，无机氮保持能力较弱。我国在紫色土氮去向及其对环境的影响、提高氮肥利用率等方面已进行了较多的研究，但最本质的紫色土氮转化特性及其与氮肥去向间关系则尚不清楚。农业利用及其利用方式不仅影响紫色土的发育速度，而且影响氮转化过程。本项目通过采集森林、旱作和水田利用方式下不同发育程度的紫色土系列，以15N成对标记结合模型数值优化分析方法测定土壤氮初级转化速率为基本手段，研究森林、旱作和水田利用方式下不同发育程度的紫色土系列土壤氮转化特性与土壤无机氮类型和去向的关系，揭示紫色土发育过程中氮转化过程的演变规律及旱作和水稻种植对氮转化过程演变的影响，为调控紫色土氮转化演变过程，根据氮转化特点合理施用氮肥提供理论依据。

本项目通过采集森林、旱作和水田利用方式下不同pH紫色土系列，采用15N同位素标记、15N示踪模型等方法，分别研究了1）不同土地利用方式下紫色土氮净转化及N2O产生速率；2）不同pH紫色土好氧条件下氮初级转化过程速率、厌氧条件下反硝化速率。研究结果表明，紫色土硝化活性因土壤母质、pH、土地利用方式不同而存在差异。pH是影响氮素净转化速率的重要因素之一。紫色土初级硝化速率的变化范围为1.19~9.05 mg N kg-1 d-1，土壤氮初级硝化速率随pH的增加而显著增加（P<0.05）。好氧条件下硝化过程对N2O产生的贡献比例为71-94%。相关分析表明，N2O产生于土壤中NO2-含量呈正相关关系。紫色土反硝化速率的变化范围为0.032-0.253 mg N kg-1 h-1。紫色土反硝化速率随pH的升高而显著增加。反硝化速率与初级硝化速率呈显著正相关关系（P<0.05）。综合以上分析，紫色土氮初级硝化速率是控制NO3-反硝化、淋溶及N2O排放的关键因素,调节紫色土初级硝化速率是增强其“保氮”能力的关键。研究结果可为依据紫色土氮转化特征制定氮肥施用计划提供依据。