三峡库区农桑配置对地表氮磷流失的影响

Effects of Crop/Mulberry Intercropping on Surface Nitrogen and Phosphorus Losses in Three Gorges Reservoir Area

为优化三峡库区紫色土旱坡地农桑配置方式,提高库区水土保持效果和生态环境效益,本试验通过采用三带等高桑＋等高耕作、三带等高桑＋交叉耕作、两带等高桑＋等高耕作、两带等高桑＋交叉耕作、传统等高耕作等5种处理研究了不同农桑配置方式对旱坡地地表氮磷流失的阻抗效果。结果表明,农桑配置方式能够显著阻抗地表径流和氮磷流失,但不同配置方式间存在显著性差异;三带等高桑＋交叉耕作方式较其他方式能更显著地降低地表径流中全氮（磷）、可溶性氮（磷）、颗粒态氮（磷）的流失和氮（磷）年流失负荷量,地表径流中氮、磷流失分别以可溶性氮（约50.1%~60.2%）和颗粒态磷（约54.9%~59.6%）为主,并且硝态氮的年流失负荷（约0.19~0.27kg hm-2 a-1）高于铵态氮（约0.12~0.17 kg hm-2 a-1）。综上可知,三带等高桑＋交叉耕作对地表径流和氮、磷流失的阻抗效果更显著,最符合三峡库区旱坡地开发利用的生态保护理念。

Aquatic ecosystems are seriously threatened because of fragile Eco-environment and severe non-point pollution in Three Gorges Reservoir Area of China. Crop/mulberry intercropping is popular because of efficiency to reduce nitrogen（N）and phosphorus（P）loss and control agricultural non-point source pollution. However,there is a huge controversy to achieve optimal crop/mulberry intercropping in the Three Gorges Reservoir Area. In order to optimize the crop/mulberry intercropping pattern in purple dry slope-land so as to improve its effects of soil and water conservation and eco-environment benefits in the Three Gorges Reservoir Area,an experiment with five treatments（i.e. Treatment I：Contour tillage with contour mulberry tree lines on upper-slope,middle-slope and lower-slope,Treatment II：Cross cultivation with contour mulberry tree lines on upper-slope,middle-slope and lower-slope,Treatment III：Contour tillage with contour mulberry tree lines on middle-slope and lower-slopes,Treatment IV：Cross cultivation with contour mulberry tree lines on middle-slope and lower-slopes and Treatment V：Conventional contour tillage.）was carried out in Wangjiagou catchment of the Three Gorges Reservoir Area from January 1,2014 to December 31,2014. N and P in surface runoffs was analyzed for forms（ammonium nitrogen,nitrate nitrogen,total nitrogen（TN）,dissolved nitrogen（DN）,particulate nitrogen（PN）and total phosphorus（TP）,dissolved phosphorus（DP）,particulate phosphorus（PP））and annual loading of N and P loss with surface runoff was assessed. Results showed that on the whole,crop/mulberry intercropping significantly retarded N and P losses with surface runoffs,but the effect varied sharply with rainfall intensity and pattern of the intercropping. Treatment II was the most effective in retarding the loss of TN,DN,PN,TP,DP and PP,regardless of rainfall intensity and Treatment III came the next. However,under rainfalls moderate or low in intensity（44.2 mm d-1 and 53.9 mm d-1）,Treatment I was the most effective in retarding the loss of ammonia nitrogen and nitrate nitrogen,while under rainfalls high in intensity（122.4 mm d-1）,Treatment I was obviously lower than Treatment II and Treatment III in such an effect. Furthermore,the treatments also differed sharply in annual loading of N and P loss with surface runoff because the effects of cultivation practice,location of contour mulberry tree lines,and their interactions on N and P losses were different. Compared with Treatment V,Treatment III reduced TN by 12.8%,TP by 19.3%,DN by 20.2%,DP by 10.9% and PP by 25.7%;Treatment IV reduced TN by 41.7%,TP by 44.7%,DN by 44.7%,DP by 38.1%,PN by 36.1% and PP by 48.5%;Treatment I reduced TN by 23.7%,TP by 42.5%,DN by 25.5%,DP by 40.2%,PN by 19.7% and PP by 44.1%;and Treatment II reduced TN by 43.6%,TP by 58.8%,DN by 45.7%,DP by 55.4%,PN by 39.3% and PP by 61.1%. The nitrogen and phosphorus lost with runoff were dominated with DN（approximately 50.1%~60.2%）and PP（approximately 54.9%~59.6%）,and the annual loading of NO3--N loss（approximately 0.19~0.27 kg hm-2 a-1）was higher than that of NH4＋-N loss（approximately 0.12~0.17 kg hm-2 a-1）. In conclusion,because of combined effects of cultivation practice,location of contour mulberry tree lines,and their interactions on surface N and P losses,four kinds of crop/mulberry intercropping practices reduced surface runoffs,N and P concentration in surface runoff caused by each rainfall event,and N and P annual loading. But treatment II（cross cultivation with contour mulberry tree lines on upper-slope,middle-slope and lower-slope）is more pronounced in retarding and controlling N and P loss with surface runoff,and therefore it is an optimal intercropping pattern for exploiting the resources of purple dry slope-land in the Three Gorges Reservoir Area of China.