冻融交替对农田氮磷淋溶影响的研究进展

农田施肥过量导致氮磷养分淋溶引发的水体污染问题日益突出,冻融交替是中高纬度、高海拔和部分温带地区的自然现象,对冻土区农田生态系统的土壤生物地球化学过程有重要影响。了解冻融交替如何影响土壤氮磷养分淋溶,对建立阻控养分淋溶的措施至关重要。本文对国内外已有的研究结果进行归纳和梳理,从土壤物理、化学和生物学角度阐述了冻融交替对农田土壤氮磷淋溶的作用机制和影响因素。冻融交替主要是通过以下几个方面影响养分淋溶:1)土壤水的相变对土壤颗粒、孔隙结构、微生物细胞的破坏作用;2)对土壤微生物群落组成、结构及其参与的养分循环的影响; 3)最终导致土壤对养分和水分固持能力、可淋溶养分的含量和形态以及淋溶通道的改变。此外,气候因素包括气温和积雪覆盖对冻融模式的影响以及土壤自身的性质决定着冻融期间养分淋溶损失程度。基于冻融对养分淋溶的影响机制,阐述了增施生物炭、种植覆盖作物、采用免耕秸秆覆盖等耕作方式在减缓养分淋溶方面的研究进展和潜在机制,为今后相关研究工作提供了理论依据。最后简要指出当前研究的不足之处,提出未来相关研究的方向。

A review of the freeze-thaw cycling effect on arable soil nitrogen and phosphorus leaching

Excessive agricultural fertilization has caused nutrient leaching and severe surface and groundwater pollution in recent years. Soil freeze-thaw cycling (FTC) is common at middle and high latitudes, high altitudes, and partial temperate regions. FTC plays an important role in soil biogeochemical processes in cold regions and may be complicated by climate change. Understanding the effects of FTC on soil nitrogen (N) and phosphorus (P) leaching is critical for effective mitigation. This study reviewed the involvement of FTC on soil nutrient leaching based on soil physical, chemical, and biological properties and found that FTC affects soil nutrient concentrations, leachate forms, and nutrient leaching pathways. FTC damages soil aggregates, microbial cells, and plant root residues, leading to the release of organic matter and various N and P forms into the soil, subsequently stimulating soil mineralization and increasing the mineral nutrient concentrations. Soil hydrothermal regime variations and soil structure changes during the FTC period promote preferential flow, thereby increasing the nutrient leaching potential. FTC affects the soil microbial biomass and the microbial community composition and structure, which changes the nutrient cycling processes. Soil chemical properties, including organic matter, pH, and cation exchange capacity, indirectly influencing soil aggregate stability, microbial resistance, and nutrient holding capacity changed during the FTC period. Soil properties (e.g., soil texture, organic matter content, and soil moisture) and climate (e.g., air temperature and snowpack) determine the nutrient leaching degree during the FTC period. The relationships between nutrient leaching and existing agricultural practices were also analyzed. Mineral fertilizer application is the primary source of nutrient leaching on farmlands. Therefore, fertilizing for the efficient use of nutrients by plants is crucial for mitigating nutrient leaching. Other practices, such as biochars, cover crops, no-tillage with straw mulching, may have a role in reducing nutrient leaching. Biochars have a high sorption capacity and may increase the soil water and nutrient holding capacity, cover crop implementation may absorb excess fertilizer nutrients from the soil and reduce leachable N and P, and no-tillage with straw mulching may change FTC by avoiding exposed soil and influencing soil physicochemical and microbial properties, thereby increasing fertilizer efficiency. However, these measures have shortcomings; cover crops and crop residues are the nutrient leaching sources during FTC. Further research is needed to understand the nutrient leaching mechanisms of these practices and to establish a complete evaluation system.