不同土地利用方式下红壤磷素径流流失特征

土壤磷素流失已成为地表水富营养化的重要威胁,红壤在我国分布范围广、分布面积大,研究红壤磷素累积与流失特征可为红壤区农业面源污染控制、防止区域地表水污染提供科学依据。选取红壤区牧草地、休闲地、玉米地、菜地、大棚5种常见土地利用方式,采用人工模拟降雨方法,研究了红壤区不同土地利用方式下磷素累积状况、形态组成和随地表径流的迁移特征及其环境阈值。结果表明:(1)供试土壤Olsen-P含量的范围为6.81～178.17 mg/kg,土壤溶解态活性磷(CaCl_2-P)含量的范围为0.29～8.26 mg/kg,藻类可利用总磷(NaOH)的变化范围为30.34～369.81 mg/kg,不同利用方式红壤中均存在一定程度的磷素累积;(2)不同利用方式红壤的磷吸持指数PSI范围为31.95～47.05,均值大小表现为牧草地玉米地菜地休闲地大棚;(3)红壤地表径流中TP的浓度范围为0.245～2.073 mg/L,TDP浓度范围为0.023～0.308 mg/L,PP浓度范围为0.223～1.826 mg/L,不同场次降雨地表径流中TP和PP平均浓度和流失量大小与土壤表层Olsen-P含量分布规律一致,TDP平均浓度表现为大棚菜地旱地玉米牧草地休闲地,而TDP流失量却表现为大棚菜地牧草地休闲地旱地玉米;径流输出以PP为主,占TP的比例为82.46%～90.15%;(4)土壤Olsen-P与NaOH-P和CaCl_2-P存在极显著正相关,随着Olsen-P含量的增加,NaOH-P和CaCl_2-P提高,且Olsen-P与NaOH-P之间存在一个明显的"突变点",确定36.17 mg/kg为红壤磷素流失的环境阈值,同时还指出,径流TP浓度或流失量与土壤NaOH-P含量呈显著正相关。

Characteristics of Phosphorus Runoff Loss in Red Soil Under Different Land Use Patterns

The loss of soil phosphorus has become an important threat to the eutrophication of surface water. Red soil is widely distributed in China, and its distribution area is large. The study on phosphorus accumulation and loss in red soil can provide scientific basis for controlling agricultural non-point source pollution and preventing regional surface water pollution. In this study, 5 common land use patterns including pasture, leisure land, dry land corn, vegetable land, and greenhouse were selected, and using artificial rainfall simulation method, the forms of phosphorus accumulation, the characteristics of phosphorus transfer with surface runoff and the environmental threshold under different land use types in red soil region were studied. The result showed that: (1) Soil Olsen-P contents of red soils ranged from 6.81 to 178.17 mg/kg, CaCl₂-P contents ranged from 0.29 to 8.26 mg/kg, and NaOH contents ranged from 30.34 to 369.81 mg/kg, P accumulated in red soil among the different land use patterns; (2) The PSI ranged from 31.95 to 47.05 in red soil under different land use patterns, and the mean values were as follows: Grassland > Corn field > Vegetable field > Leisure area > Greenhouse; (3) The concentration of TP in surface runoff of red soil was 0.245~2.073 mg/L, TDP was 0.023~0.308 mg/L, and PP was 0.223~1.826 mg/L under different land use patterns. The average concentrations and losses of TP and PP in surface runoff of different rainfall events were consistent with the Olsen-P content in the soil surface layer, the average concentrations and losses of TDP in the order of greenhouse > Vegetable field > Corn field > Grassland > Leisure area and Greenhouse > Vegetable field > Grassland > Leisure area > Corn field, respectively. PP was the dominant form of TP in runoff under different land use patterns, which account for 82.46%~90.15% of TP; (4) There was a very significant positive correlation between soil Olsen-P and NaOH-P and CaCl₂-P. As the content of Olsen-P increased, the NaOH-P and CaCl₂-P increased, and there was an obvious "Change-point", 36.17 mg/kg was determined as the red soil phosphorus environmental threshold. It was also pointed out that there was a significant positive correlation between the runoff TP concentration or loss and soil NaOH-P content.