不同施肥模式下黑土磷素垂直迁移规律与淋失特征研究

In recent years, there is increasing evidence that available phosphorus (P) remains at high levels in black soil of Northeast China and has a great potential to be transferred to subsoil by leaching. In addition, the continual input of phosphate and organic fertilizers under the traditional agricultural practice aggravates the downward P loss attributed by preferential flow through macropores, which is more likely enhanced by seasonal freeze-thaw cycles under the special climate. As a result, the problem of P loss in black soil of Northeast Chinastands out undoubtedly. Hence, to investigate the specific relationship among the accumulation of TP(Total P) and Olsen-P andthe quality and quantity of P fertilizers, and the vertical P transport and leaching characteristics, is of significant importance to balanced fertilization and sustainable agricultural development for this region. Based on the agricultural experiment base in Gongzhuling, Jilin Province, this project carries out both in-situ field experiment and intact soil columnleaching experiment using the techniques of 31P-NMR(Nuclear Magnetic Resonance Spectroscopy), dye-tracing and X-ray CT scanning, to study the dose-effect relationship between available P accumulation and fertilization in different layers of black soil under different fertilization modes, and to ascertain the vertical distribution characteristics, migration patterns and leaching risk of various forms of P in black soil profile. Along with the quantification of the contribution of water flow (preferential flow and matrix flow) to the vertical transport of soil P, this project can provide theoretical basis for agricultural safety, balanced and efficient P application in black soil area of Northeast China, and reducing the environmental risk caused by P application.

当前我国东北黑土区土壤有效磷水平已较高且易发生淋溶损失，而黑土区常规作物种植施肥模式仍不断施入磷肥和有机肥，加上季节性冻融等特殊的气候条件增加了土壤大孔隙优先流，致使黑土区磷素淋失问题更加突出。因此研究不同施肥模式下黑土全磷和有效磷积累与施肥间的量效关系，磷素垂直迁移规律与淋失特征对东北黑土区合理施肥和农业可持续发展具有重要意义。本项目依托吉林省公主岭黑土田间原位监测基地，采用田间原位试验和原状土柱田间淋溶试验相结合的方法，利用磷核磁共振（31P-NMR）、示踪染色与CT扫描技术，系统研究长期不同施肥模式下黑土不同剖面层之间有效磷积累与施肥间的量效关系；探明黑土剖面各形态磷素的垂直分布特征、迁移规律及其淋失风险；并结合黑土孔隙特征量化土壤各水流途径（优先流、基质流）对土壤磷垂直运移的贡献，为我国东北黑土区农业安全、合理、高效施磷，降低因施磷导致的环境风险提供理论依据。

我国东北黑土区土壤有效磷水平较高，而区域内常规作物种植施肥模式中磷素仍源源不断施入土壤中，致使磷素淋失风险日益增加。本研究依托东北黑土不同施磷处理中长期田间定位实验，系统研究了不同施磷量及不同磷素来源（有机肥、磷肥）条件下土壤磷素在1米剖面内的形态、组成及累积分布规律；依托玉米典型施肥模式中长期田间定位试验，通过土壤原位土柱连续多年观测淋溶液，分在剖面中的积累与垂直布规律，并结合亮蓝染色示踪技术和 CT扫描技术，系统研究了不同施肥模式下土壤中磷素淋溶损失的量级、形态、季节和年度的变化规律，以及不同层次土壤的孔隙特征，建立了施肥、孔隙、磷素淋溶三者之间的关系模型。主要研究结果如下：（1）常量化肥磷主要提高的是中等稳定态磷HCl-P，而增施50%磷肥仅使表层活性态磷累积明显。有机肥替代25%磷肥和替代50%磷肥处理与常量化肥磷相比在磷素累积的整体水平上差异不大。活性态、中等活性态和稳定态磷组分对土壤Olsen-P含量有较高的解释度，土壤中各个形态磷库间存在相互转化的现象，并共同维持土壤中Olsen-P水平的稳定。（2）东北黑土区常规施肥模式中，每年淋溶损失的磷量占当年施磷量的0.78%-1.62%，1m土层处淋溶液中溶解态磷和颗粒态磷的比例约为1：1，溶解态磷中无机磷和有机磷的比例约为3：2。不同施肥模式对1米深度土壤淋溶液中磷素形态组成有显著影响。（3）CT扫描表明不同施肥模式5年后0-40 cm土壤孔隙结构发生明显改变。其中，单施化肥使土壤孔隙更加致密，而秸秆还田和在此基础上配施适量动物粪肥可以指数型增加土壤大孔隙（等效直径 > 1 mm）、中孔隙（0.2- 1 mm）和长孔隙（孔隙长度 > 1 mm）的数量，从而增加土壤孔隙的连通性和各向异性，这些差异与外源有机肥输入带来大量的有机碳密切相关，大孔隙优先流是磷素淋失的主要途径。综上，黑土区典型施肥模式下磷素的淋失量仅占当年施磷量的1%左右。秸秆还田可在一定程度上可以减少磷素的淋失；而有机肥施用可增加土壤大孔隙，使磷素在各个土层累积，加剧磷素淋失风险。