三峡库区紫色土坡耕地不同桑树-作物配置模式下土壤氮磷的淋溶

Leaching losses of nitrogen and phosphorus from arable hillslope purple soils under different mulberry-crop combinations in Three Gorges Reservoir Region

利用混合离子交换树脂填埋吸附法对重庆市涪陵区王家沟小流域内4种不同桑树-作物配置模式下的坡地土壤氮磷淋溶量进行了定量化研究。试验所设置的4个处理分别为横坡农作、横坡农作+三带桑树、横坡农作+四边桑树、横坡农作+等高桑树+四边桑树。各处理耕作、施肥措施均保持一致,作物种植制度为玉米-榨菜轮作。结果表明,玉米季各处理土壤总氮(TN)的淋溶量在10.19~11.37 kg·hm^(-2)之间,榨菜季在11.06~12.23 kg·hm^(-2)之间,同一季不同处理间或同一处理不同季间土壤TN的淋溶量差异均不显著(P>0.05)。硝态氮(NO_3^--N)和铵态氮(NH_4^+-N)对TN年淋溶量的平均贡献率分别为63.9%和36.1%,说明NO-3-N是氮素垂直淋失的主要形式。同一处理土壤在榨菜季的NO_3^--N淋溶量均高于玉米季,NH_4^+-N则相反;不同处理土壤总磷(TP)年淋溶量范围为0.19~0.21 kg·hm^(-2),处理间无显著差异(P>0.05)。不同桑树配置模式对土壤氮磷淋溶拦截效果的差异并不明显,可能是由本试验中的桑树种植年限较短及根系还不发达所致。

A field monitoring was carried out at the Wanjiagou catchment of Fuling District in the Three Gorges Reservoir Region, to quanti-fy the vertical leaching losses of nitrogen（N）and phosphorus（P）from arable hillslope purple soils under different mulberry-crop systems by employing mixed ion exchangeable resin burying and adsorption method. The experiment consisted of four treatments, i.e., contour culti-vation, contour cultivation with mulberry trees planted on the upper, middle and lower slopes, contour cultivation with mulberry trees planted on the four sides of the slope, and contour cultivation with mulberry trees planted on the four sides of the slope and the middle slope. All ex-perimental plots received the same tillage and fertilization treatments and were subjected to a maize-mustard rotation system. Results showed that leaching rates of total N（TN）from soils under different treatments varied from 10.19 to 11.37 kg·hm-2 for the maize-cropping 〈br〉 season and from 11.06 to 12.23 kg·hm-2 for the mustard-cropping season. The loss of TN was not significantly different among different treatments during the same cropping seasons or between different cropping seasons for the same treatments（P〉0.05）. The contribution of nitrate-N and ammonium-N to the annual TN loss averaged 63.9% and 36.1%, respectively, indicating that nitrate dominated in the N leaching loss. For the same treatments, the leaching loss of nitrate-N was greater during the mustard season than during the maize season, and vice versa for the loss of ammonium-N. The annual leaching loss of total P（TP）from soils ranged from 0.19~0.21 kg·hm-2, and no sig-nificant differences were found among different treatments（P〉0.05）. The poor development of mulberry-root systems associated with the short planting duration may fail in differentiating the retention capacity of N and P leaching loss among different treatments.