太湖稻麦轮作区磷肥减施土壤磷素周转特征与供给机制

The need for efficient use of phosphorus (P) in agriculture has been highlighted recently by concerns about the finite amount of P fertilizer resources. Crop production in the Taihu Lake Region (TLR) of China has been greatly improved by increasing P fertilizer input, but overuse of P has led to a dramatic spike in P accumulation, low P use efficiency, and increased environmental risk. In our previous study, we found that P fertilization only during the wheat-growing season produced grain yields as well as the traditional P fertilization regime, P fertilization during both the rice- and wheat-growing seasons, while it maintained soil Olsen-P accumulation and phosphate utilization efficiency. However, soil P transformation characteristics and supply mechanism under the regime of phosphate reduction is unclear. This project will be proposed on our field experiments of phosphate reduction, study soil P fractionation and transformation using 31P-NMR and oxygen isotopic composition of soil phosphate fractions; investigate P biological effectiveness and release kinetics in situ, especially in rhizosphere soil, combined with the diffusive gradient in thin films (DGT) technique and high-resolution chemical imaging; clarify P distribution in the crop and soil, set up the relationship of soil P annual supply capacity and the crop total P response; and seek the adaptive mechanism of soil P supply meeting P demand of rice growth. The results will provide the theory and technology of phosphate reduction and use efficiency increase in TLR.

当前太湖流域农业生产中普遍存在磷肥养分利用率低、资源浪费严重、面源污染突出等问题。本申请在前期研究中阐明了稻季不施磷的减磷措施在稳产的同时能够节约资源、减少环境风险。然而，磷肥减施下土壤磷素的周转特征与供给机制却不清楚。因此，本项目拟依据已有的太湖稻麦轮作农田磷肥减施定位试验，按照修正的Hedley分级方法，结合31P-NMR与土壤磷酸盐氧同位素技术，研究土壤磷素的赋存形态及转化特征；借助薄膜扩散梯度技术(DGT)以及高分辨测定技术原位探讨磷在土-水界面和根际微区的生物有效性及释放动力学；阐明磷素养分周年运筹与其在作物及土壤中的分配特征，建立土壤磷素周年供给能力与作物磷素吸收的动态响应关系；同时探究减磷土壤中磷供给满足水稻生长磷需求的适应性机制。研究结果将为稻麦轮作农田磷肥减施增效的理论和技术体系提供科学依据。

当前太湖流域农业生产中普遍存在磷肥养分利用率低、资源浪费严重、面源污染突出等问题。本项目依据中国科学院常熟农田生态系统国家野外可续观测研究站长期定位试验点，从磷循环角度（包括磷输入途径及输入量、磷输出途径及输出量）计算了磷平衡，阐明了磷素养分周年运筹与其在作物及土壤中的分配特征，建立了土壤磷素周年供给能力与作物磷素吸收的动态响应关系。研究结果表明稻麦轮作农田均施磷肥处理（40 kg P2O5 ha-1每季）能基本保持磷输入输出平衡，稻季不施磷麦季施磷的磷肥减施处理磷平衡为负值，但是能够维持作物产量及磷吸收，因此土壤累积态磷在磷肥减施过程中发挥着非常重要的作用。进一步按照修正的Hedley分级方法，结合31P-NMR与土壤磷酸盐氧同位素技术，研究了稻季不施磷减磷措施下土壤磷素的赋存形态及转化特征，揭示了传统稻麦季均施磷肥处理下，土壤利用的主要是NaHCO3-Pi，而稻季不施磷的磷肥减施处理主要利用土壤中NaHCO3-Pi以及NaOH-Pi；同时借助DGT技术结合高分辨测定方法原位探讨了土壤尤其根际微区磷的生物有效性及释放动力学，发现稻季不施磷减磷措施能够维持土壤中的有效磷源供给，水稻根际土壤中磷供给充足，且磷的移动与释放受铁循环控制。研究结果最终回答了稻麦轮作农田稻季不施磷土壤磷素周转特征与供给机制，为磷肥减施增效的理论和技术体系提供科学依据。