“以碳调氮”阻控旱地农田土壤酸化的机制

Soil acidification of cropland is increasingly serious in China. Excess application of nitrogen (N) fertilizer induces intensive nitrification and loss of nitrate, which is the dominant factor for soil acidification in dry land. Addition of organic materials (organic carbon) could not only promote the microbial immobilization of inorganic N and consequently decrease nitrification and loss of nitrate, but also neutralize soil acidity. Thus, the addition of organic carbon coupled with N fertilizer may inhibit soil acidification. However, this idea got little attention. Thus, typically acid soils with different parent material and utilization type from dry land would be collected in this study. N nitrification, abiotic and microbial immobilization, and their relationship with these soil physicochemical and microbial properties would be investigated. Effect of organic materials on these N transformation processes would be identified. The isotope tracing technique with 15N combined with FLUAZ model, biomarker, and selectively biochemical inhibitors would be used to explore the mechanism in using organic carbon to adjust N transformation and inhibit soil acidification in the dry land. The technique principle of using organic carbon to adjust N transformation and inhibit soil acidification would be proposed. Effect of the technique on increasing N use efficiency and inhibiting soil acidification would be identified and optimized with pot and field experiments. The results obtained in this study may enrich the knowledge of soil N cycling and provide a scientific basis and technological support for soil acidification inhibition and high N use efficiency.

我国农田土壤酸化日益严重，氮肥过量施用引起大量氮的硝化和硝态氮的淋失是加速旱地农田土壤酸化的主要原因。外加有机物料不但可以促进土壤中氮的微生物同化，减少氮的硝化和淋失，而且可以中和土壤酸度，因此能够阻控土壤酸化。但这种“以碳调氮”阻控土壤酸化的方法还缺乏系统研究。本项目拟从我国采集不同母质和利用类型的旱地农田土壤，深入研究土壤中肥料氮的硝化、非生物固持和微生物同化作用及其与土壤理化和微生物性质的关系，以及易利用碳源和有机物料对肥料氮转化过程的影响。利用15N示踪技术结合FLUAZ模型、生物标记物和选择性生化抑制剂等方法揭示“以碳调氮”调控土壤氮转化和阻控酸化的机制，构建有机物料“以碳调氮”阻控土壤酸化的技术原理，通过盆栽和田间实验验证该技术提高氮肥利用率和阻控土壤酸化的效果、并优化调控方案。研究结果将丰富氮素循环过程的认识，并为我国农田土壤酸化阻控和氮肥高效利用提供理论依据和技术支撑。

我国农田土壤酸化日益严重，氮肥过量施用引起大量氮的硝化和硝态氮的淋失是加速旱地农田土壤酸化的主要原因。外加有机物料不但可以促进土壤中氮的微生物同化，减少氮的硝化和淋失，而且可以中和土壤酸度，因此能够阻控土壤酸化。但这种“以碳调氮”阻控土壤酸化的方法还缺乏系统研究。本项目主要研究了旱地土壤氮肥转化影响土壤酸化的作用及其关键的控制因子、外源有机碳调控旱地土壤肥料氮的转化和酸化的作用、以及“以碳调氮”提高氮肥利用率和阻控旱地土壤酸化的效果验证。研究发现酸性旱地土壤存在明显的硝化作用，且硝化速率为菜园土壤>农田土壤>茶园土壤，尿素对硝化的促进作用明显强于硫酸铵。旱地土壤的硝化作用主要受土壤pH和AOB丰度，特别是cluster 3物种的控制，而且硝化作用越强，其促进土壤酸化的作用也相应增强。增加土壤中有机碳的生物有效性可以促进微生物对氮素的同化作用，具有减少旱地土壤氮素损失和抑制土壤酸化的潜力。其中外源添加有机碳与肥料氮比值高于20即可明显促进微生物氮同化和酸化阻控作用，添加的C/N比越高，其作用越强；添加的C/N比在20-40范围内有利于肥料氮的短期缓冲缓释，高于40则有利于肥料氮的土壤固持。易利用和中等易利用的糖类有利于促进前期肥料氮的微生物同化作用及其后期有机氮的矿化作用，对肥料氮在作物生长季起缓存缓释作用，有机酸盐的相应作用较弱，但可通过脱羧作用快速消耗质子而提高土壤pH，而难利用的木质素类同化作用弱，但具有抑制硝化和提高土壤酸缓冲性能的作用。8年长期定位试验证明施用有机物料可以通过“以碳调氮”作用提高氮肥利用率和阻控氮肥诱导的土壤酸化。研究结果为我国农田土壤酸化阻控和氮肥高效利用提供理论依据和技术支撑。