褐土区氮磷在土壤发生层中淋溶的差异性

农业氮磷淋溶已经成为地下水污染最普遍和突出的问题。为揭示氮磷在包气带不同土层的淋溶特征，以典型褐土的5个土壤发生层（耕层、淋溶层、钙积层、黏化层和母质层）为研究对象，采用室内土柱模拟淋溶试验，在施肥量相同的条件下分析不同形态氮磷淋溶量，研究氮磷在不同土壤发生层中的迁移特征及其影响因素。结果表明：1）进行5次淋溶，耕层、淋溶层、钙积层、黏化层和母质层淋溶液中可溶性总氮总量分别为2412.63 mg·L^-1、3028.94 mg·L^-1、244.16 mg·L^-1、3648.99 mg·L^-1和3356.51 mg·L^-1，淋溶层、黏化层和母质层可溶性总氮淋溶量显著高于耕层，而钙积层可溶性总氮淋溶量较耕层显著减少；耕层淋溶液中可溶性总磷总量为0.52 mg·L^-1，且显著高于其他4层。2）在试验初期，耕层、淋溶层的硝态氮、可溶性总氮和正磷酸盐淋溶量显著高于黏化层和母质层，进行到第4、5次淋溶，黏化层、母质层的硝态氮和可溶性总氮淋溶量显著高于其他3层，而各发生层间正磷酸盐淋溶量无显著差异；单次淋溶黏化层和母质层铵态氮淋溶量均显著高于其他3层，而耕层可溶性总磷淋溶量始终显著高于其他各层。3）耕层和钙积层的淋溶液中硝态氮是氮素淋溶的主要形态，占可溶性总氮比例分别为69.0%和85.4%，而在淋溶层、黏化层和母质层中分别为41.3%、5.1%和4.6%；在可溶性磷中，以无机态正磷酸盐为主，最高占可溶性总磷的75.9%。4）土壤有机质含量、阳离子交换量、黏粒含量对土壤氮磷的迁移转化有明显主导作用。有机质与氮磷淋溶量呈显著正相关关系，有机质含量高，会增加淋溶初期氮磷的淋溶风险；而阳离子交换量和黏粒含量则与氮磷淋溶呈显著负相关关系，阳离子交换量大和黏粒多能减少氮磷素的淋溶风险。该试验结果说明，由于5种发生层土壤理化性质不同，各发生层氮磷淋溶特征及其淋溶形态也有差异，并且氮磷的淋溶受土壤本身阳离子交换量、黏粒和有机质含量的影响。

Nitrogen and phosphorus leaching differs among cinnamon soil layers

Leached agricultural N and P are the most prominent groundwater pollutants. Five cinnamon soil layers (cultivation, leaching, calcium, clay, and parent) were analyzed via leaching tests to investigate N and P migrations. After five tests, the amount of soluble total N in the leaching solutions were 2412.63 mg·L^-1 in cultivation layer, 3028.94 mg·L^-1 in leaching layer, 244.16 mg·L^-1 in calcium layer, 3648.99 mg·L^-1 in clay layer, and 3356.51 mg·L^-1 in parent layer. The amount of soluble total N in the leaching, clay, and parent layers was significantly higher than that in the cultivation layer but that of soluble total N in the calcium layer was significantly lower than that in the cultivation layer. The amount of soluble total P in the cultivation layer leaching solution was 0.52 mg·L^-1, which was significantly higher than that in all other layers. In the 1st to 3rd leaching time, the leached amounts of nitrate nitrogen, soluble total N, and orthophosphate in the cultivation and leaching layers were significantly higher than those in the clay and parent layers. However, in the 4th and 5th leaching time, the leached amounts of nitrate nitrogen and soluble total N in the clay and parent layers were significantly higher than those in the other layers, and the leached orthophosphate amount did not differ among layers. The amount of leached ammonium nitrogen in the clay and parent layers was significantly higher than that in the other layers after each test, and that of soluble total P in the cultivation layer was always significantly higher than that in the other layers. Nitrate nitrogen was the primary form of leached N in the cultivation and calcium layers, accounting for 69.0% and 85.4% of the total amount of N, respectively; the nitrate nitrogen percentages in the other layers were 41.3% (leaching layer), 5.1% (clay layer), and 4.6% (parent layer). Inorganic orthophosphate was the primary form of soluble P, accounting for 75.9% of the total amount of soluble P. The soil organic matter content, cation exchange capacity (CEC), and clay content affected the migration and transformation of soil N and P. There was a significant positive correlation between organic matter and N and P leaching, and more organic matter content increased the leaching risk in the initial leaching stage. The CEC and clay content were negatively correlated with N and P leaching, and increased CEC and soil clay particles reduced the leaching risk. The physical and chemical properties and N and P leaching characteristics differed among soil layers, and leaching was affected by soil CEC, clay and organic matter contents.