农林复合系统中物种间水肥光竞争机理分析与评价

低丘红壤农林复合系统被认为能通过引入树木而利用土壤深层水分及防治水土流失，从而作为亚热带地区应对季节性干旱的有效利用方式。然而，复合也可引起光能、水分和养分的竞争，导致农作物减产。通过作物生长量的测定、利用多年监测的土壤水文数据、15N微区试验及光合有效辐射的测量，综合探讨了南酸枣-花生复合系统引起的物种间水肥光的变化；通过其交互作用形成的协同，竞争关系分析，较为全面地评价了农林复合系统水肥光竞争特征。研究表明：低丘红壤上南酸枣与花生复合，促进了南酸枣生长，却减小了20％～50％的花生产量和生物量。其原因不单是南酸枣遮荫引起复合花生光合有效辐射减弱，还与水、肥竞争有关。复合系统在旱季加大利用50～100cm土层土壤水分，从而缓冲了干旱造成的影响；但南酸枣与花生间作系统也存在着一定的水分竞争。复合使得南酸枣能够利用施于花生区及淋失到60cm深处的养分，提高了养分的利用率；但同时也导致养分的竞争并影响花生的生长。在花生产量、生物量受复合南酸枣竞争影响因子中，以光最大、养分其次、水分最小。农林复合系统水肥光交互作用因其组分类型与时空配置而异，需从生态、经济、社会效益方面对复合模式加以优化。

Assessment of competition for water, fertilizer and light between components in the alley cropping system

Alley cropping systems can positively utilize deep soil water and leached nitrogen in the dry season,and help prevent soil and water erosion in the rainy season.In the surface soil,however,competition for nitrogen and water,and above the ground the competition for sunlight between the components may occur.The objective of this paper was to assess the alley cropping system,consisting of Choerospondias axillaris trees and peanut(Arachis hypogaea) plants in subtropical China in terms of uses of soil water,soil nitrogen and light.()~(15)N injection experiments were carried out to determine N use by tree and crop.Spatial variations of photosynthetic available radiation(PAR) were measured to determine the shadowing effect.Spatial and temporal variations of soil water regime were monitored to determine the competition for water between the trees and peanut plants.In addition,crop and tree growth were also recorded.Compared to the tree alone systems,alley cropping systems encouraged the fast growth of the trees,and depressed the biomass and yield of peanut by 20% to 50%. The impact of PAR was profound and had a negative relationship to the biomass and yield of peanut plants.The spatial and temporal variations of soil water regime indicated that the tree utilized soil water beneath the surface layer and alleviated the seasonal drought.Competition for soil water between the tree and peanut plant occurred at the beginning of the dry season.Compared with the mono-peanut cropping system,the alley cropping system decreased()~(15)N recovery by peanut plant and increased()~(15)N recovery by the tree,indicating that the tree utilized soil nitrogen leached to 60 cm depth.The yield and biomass of peanut plants were influenced mostly by light,but also by fertilizer and water.The results suggest that these competitions for resources must be taken account to optimize the alley cropping system.