经营模式对大渡河干暖河谷黄果柑坡地果园土壤养分的影响

Effects of management modes on soil nutrients in sloping Huangguogan orchards in the dry-warm valley of the Dadu River

坡地果园是大渡河干暖河谷两岸一种常见的土地利用方式,大面积坡地果园垦殖导致了严重的水土流失和一定程度的氮、磷面源污染.为了解经营模式与坡位是否及如何影响果园的土壤养分,选择大渡河流域两类典型经营模式(散户和集体经营)下的黄果柑坡地果园作为研究对象,比较不同坡位(下坡、中坡、上坡)土壤养分的差异,并探讨土壤有机质(SOM)、可溶性有机碳(DOC)、可溶性有机氮(DON)及全氮(TN)、全磷(TP)、土壤铵态氮(NH4+-N)和硝态氮(NO3--N)含量与细根生物量、土壤持水性能等的关系.结果显示:与下坡位相比,中上坡位的土壤养分(SOM、TN、DON、DOC)含量降低,表明下坡位出现土壤养分的聚集现象;与散户经营的坡地果园相比,集体经营的坡地果园中每土层TN、DON、NH4+-N、NO3--N含量分别增加28%、17%、85%、72%,而SOM、DOC含量分别降低4%、3%;TP在两类经营模式的坡地果园间差异不大,每土层均值均为0.49 g/kg.不同经营模式和坡位土壤养分的差异性与不同经营模式和地形位置下的细根、土壤容重及涵水能力的差异化有关.总之,经营模式的差异会导致土壤养分循环的变化,从而影响植物对养分的吸收,不合理的经营模式将会增加坡耕地土壤氮、磷和有机质的流失,这可能是造成坡地黄果柑果园土壤养分下降的重要原因;上述结果对于指导坡地种植时控制水土流失带来的土壤养分流失和氮、磷面源污染有一定的理论与实践意义.(图3表2参56)

Sloping orchards,which are distributed in the dry-warm valley of the Dadu River,are a common landuse type.Large-scale cultivation of orchards on slope land has resulted in serious soil erosion and non-point source pollution of nitrogen and phosphorus.However,whether and how the management mode and the slope position affect soil nutrients are largely unknown.In two Huangguogan sloping orchards with typical management modes(individually managed and collectively managed),the differences in soil nutrients among three slope positions(bottom,middle,and upper slope)were compared,and the correlations among soil organic matter(SOM),dissolved organic carbon(DOC),dissolved organic nitrogen(DON),total nitrogen(TN),total phosphorus(TP),soil ammonium nitrogen(NH4+-N),soil nitrate nitrogen(NO3--N),fine root biomass,and soil water holding capacity were examined.The findings showed that compared with the bottom slope position,in the middle and upper slope positions,the mass fraction of the soil nutrients(SOM,TN,DON,and DOC)decreased,indicating a tendency for soil nutrient accumulation in the bottom slope position.Compared with the individually managed orchards,in the collectively managed orchards,the mass fractions of TN,DON,NH4+-N,and NO3--N in each soil layer increased by 28%,17%,85%,and 72%,respectively,but the SOM and DOC contents decreased by 4%and 3%,respectively.The TP content showed little difference between the management modes,and the average content in each soil layer was 0.49 g/kg.The differences in the soil nutrient contents between the different management modes and slope positions were mainly influenced by the soil fine roots,soil bulk density,and water holding capacity under different management modes and terrain locations.In conclusion,the differences in management modes will lead to changes in soil nutrient cycling,which will affect the absorption of nutrients by plants.Unreasonable management modes will increase the loss of soil nitrogen,phosphorus,and organic matter on sloping farmland,which could be the main cause of the decrease in the nutrient content in these sloping orchards.These results can provide a theoretical and practical guide for controlling soil nutrient loss and nitrogen and phosphorus non-point source pollution caused by soil and water loss in newly established sloping orchards.