施用铵态氮肥促进石灰性设施菜田土壤磷素移动的机制研究

Excessive fertilization and irrigation in vegetable greenhouse caused high accumulation of nitrogen (N) and phosphorus (P) in soil and high risk of non-point pollution. Previous studies showed that ammonium-N fertilizer addition could significantly increase P mobility in calcareous soil and strengthen the environmental risk. In this study, P forms in soil are analyzed using modified Hedley P fractionation, 31P NMR and XANES methods and, P content and forms in leachate at 90 cm soil depth are investigated with micro-lysimeter to quantify the relationship between change of P forms due to ammonium-N fertilizer application and soil P mobility in the long-term experiment. Soil pH, contents of Ca, Mg, Fe, Al and CaCO3 and the characteristic of P adsorption-desorption in relation to the contents of P, Ca and Mg in the leachate are investigated through field trial, soil incubation and soil column leaching experiments to determine the strategy to increase inorganic P mobility through soil acidification influenced by ammonium-N fertilizer application. Meanwhile, soil C/P ratio, microbial biomass C and P, soil phosphatase activity and microbial community structure (high-throughput sequencing (HTS) technology) are investigated to determine the strategies to reduce organic P mineralization and increase labile P fraction under ammonium-N fertilizer application in calcareous soil with high P accumulation. This study will provide theoretical reference for understanding the strategies to increase P mobility affected by applying ammonium-N fertilizer in calcareous greenhouse vegetable soils.

设施菜田氮磷高量累积和大水漫灌特点造成很高面源污染风险，施用铵态氮肥增加石灰性设施菜田土壤磷素移动性和环境风险。本研究基于定位试验，采用修正的Hedley磷分级、31P核磁共振（NMR）和同步辐射X射线吸收近边结构光谱（XANES）方法分析土壤磷素形态，同时运用田间渗漏池装置原位监测0-90 cm土层土壤淋洗液中磷素含量和形态，解析长期施用铵态氮肥导致的土壤磷素形态变化与磷素移动性的量化关系。结合定位试验、土壤培养和土柱淋洗实验，分析土壤pH、钙镁铁铝和CaCO3含量、磷素吸附解吸特征以及淋洗液中磷钙镁含量，解析施用铵态氮肥通过影响土壤酸性增加无机磷移动性的机制；采用高通量测序方法分析土壤微生物群落结构，结合土壤C/P比、微生物碳磷量、土壤磷酸酶活性等指标，解析铵态氮肥施用降低土壤有机磷矿化，增加易移动有机磷形态的原因。进而揭示铵态氮肥施用促进石灰性设施菜田土壤磷素移动的机制。

设施生产中盲目施用氮磷肥料虽然稳定了作物产量，但也造成了资源浪费和面源污染等环境风险。铵态氮肥施用和大水漫灌不仅导致土壤酸化和微生物活性变化，而且可能直接或间接影响石灰性土壤磷素形态转化和增加其移动性，它是土壤物理、化学和生物因素过程的综合反应，而其影响过程和因子分析尚缺乏系统的机理性研究。本项目分别利用13年的设施菜田长期定位试验、模拟淋洗试验和土壤培养试验，结合连续浸提磷分组、液体磷31核磁共振、同步辐射X射线近边吸收结构技术对土壤磷素形态进行表征，同时结合酶活性、微生物群落结构和磷相关功能基因丰度等技术，探究铵态氮肥施用对高磷设施土壤磷素形态和移动性的影响、土壤无机磷溶解性和吸附解吸特征的影响以及土壤有机磷形态转化的微生物过程，揭示铵态氮肥施用促进设施菜田土壤磷素移动性的机制。研究结果表明铵态氮肥施用可通过非生物和生物过程影响土壤磷素形态和迁移。非生物过程为长期氮肥导致高磷累积的设施菜田土壤酸化和CaCO3溶解，进而增加表层土壤磷素释放（溶解、解吸等）及剖面迁移；但土壤酸化增加了土壤铁铝氧化物对磷素的吸附固定，但在表层土壤中其作用弱于土壤酸化导致的钙磷释放作用，土壤pH和钙镁铁铝含量变化可以解释土壤无机磷素变化量的95.3％；此外，在淹水淋洗条件下，铵态氮主要通过影响土壤铁磷的释放促进了磷素淋洗。生物过程为施用氮肥导致的土壤酸化影响微生物转化和降低了土壤磷酸酶活性等，进而抑制了有机磷矿化矿化作用；同时氮肥施用增加了微生物对土壤有机碳的利用，可能导致活性磷库中有机磷比例增加，因此土壤pH、CaCO3、有机碳和碱性磷酸酶能够解释土壤有机磷变化量的83.1％。在本项目中也进一步通过外源添加碳氮刺激改变土壤微生物量，研究其间接影响土壤磷素形态和转化过程。总之，对于设施高磷土壤而言，铵态氮肥施用加速了表层土壤磷素的移动，这些结果为进一步理解土壤磷素养分循环特征、阻控农田土壤氮磷面源污染有重要意义。