自然降雨下玉米秸秆堆沤还田对滇中小流域坡耕地氮素流失的影响

为探究自然降雨下不同堆沤方式秸秆还田对小流域坡耕地径流泥沙及氮素流失的影响,以滇中二龙潭流域坡耕地为研究对象,设置9种不同玉米秸秆堆沤方式,分别为CK及8种处理,各处理包括2种秸秆还田量(0.75,1.5 kg/m^2)、2种秸秆粒度(1,5 cm)、2种秸秆堆沤方式(水或水与尿素堆沤),研究烤烟坡耕地产流产沙及氮素流失特征。结果表明:(1)在4场具有典型产流的降雨中,施用较高秸秆还田量(1.5 kg/m^2)和粗颗粒秸秆(5 cm),均可有效减少坡耕地产流产沙量(10.06%~38.60%和10.07%~38.60%);(2)施用较低秸秆还田量(0.75 kg/m^2)、粗颗粒秸秆(5 cm)及未添加尿素堆沤的秸秆径流TN、NO3--N浓度低于施用高秸秆还田量(1.5 kg/m^2)、细颗粒秸秆(1 cm)及添加尿素堆沤的处理(1.96%~32.79%和3.97%~40.89%);(3)各处理下NO3--N/TN、NH4+-N/TN、PN/TN分别为63.64%~86.18%,5.31%~13.86%和5.33%~25.80%,表明坡耕地地表径流氮素主要流失形式为NO3--N,溶解态氮是径流中的主要氮素污染物;(4)施用较低秸秆还田量(0.75 kg/m^2)、粗颗粒(5 cm)秸秆、未加尿素堆沤的秸秆,泥沙TN流失浓度降低(16.87%~48.15%);(5)施用较高秸秆还田量、粗颗粒秸秆及未添加尿素堆沤可有效降低滇中坡耕地氮素的流失风险(0.32%~35.05%和54.52%~77.23%)。TN径流和泥沙流失中,以径流输出为主,占TN流失量的50.09%~71.67%。为了减少该流域氮素流失量,可选择施用较高秸秆还田量(1.5 kg/m^2)和粗颗粒(5 cm)秸秆,并依据烤烟不同生长期的吸收情况和土壤养分情况等选择少量或不添加尿素堆沤进行秸秆还田。

Effect of Compost of Corn Straws Returning Under Natural Rainfall on Nitrogen Runoff Losses in a Slope Farmland of Small Watershed in Central Yunnan Province

To explore different compost methods of straw returning on runoff, sediment and nitrogen losses in small watershed, a slope farmland in Erlongtan watershed in central Yunnan Province was chose as research object. Nine different compost methods of corn straw returning were set up: CK and 8 treatments. Each treatment included two straw return amounts to the field (0.75,1.5 kg/m²), two straw particle sizes (1,5 cm), two straw heap retting methods with urea reactor (water or water and urea stacking). In this study, the characteristics of runoff, sediment and nitrogen losses in a flue-cured tobacco slope farmland were studied. The results showed that: (1) In the 4 rainfalls with typical runoff, the application of higher straw return amount (1.5 kg/m²) and coarse grain straw (5 cm) could effectively reduce runoff and sediment losses in the slope farmland (10.06% ~ 38.60% and 10.07% ~ 38.60%). (2) The concentrations of total nitrogen (TN) and NO₃^--N in runoff under the application of lower straw return amount (0.75 kg/m²), coarse grain straw (5 cm), and compost with no urea were lower than those with higher straw amount, fine grain straw, and compost with urea (1.96% ~ 32.79% and 3.97% ~ 40.89%). (3) The proportions of NO₃^--N/TN, NH₄⁺-N/TN and PN/TN were 63.64% ~ 86.18%, 5.31% ~ 13.86% and 5.33% ~ 25.80%, respectively, and the main form of nitrogen loss in runoff on slope farmland was NO₃^--N, dissolved nitrogen was the main nitrogen pollutant in runoff. (4) TN losses concentration of sediment with the application of lower straw return amount (0.75 kg/m²), coarse grain straw (5 cm), and compost with no urea decreased (16.87% ~ 48.15%). (5) TN losses of runoff and sediment with the application of higher straw return amount, coarse grain straw and compost with no urea could effectively reduce the risk of nitrogen loss in the slope farmland in central Yunnan province (0.32% ~ 35.05% and 54.52% ~ 77.23%). Among TN runoff and sediment loss, runoff output was the main factor, accounting for 50.09% ~ 71.67% of TN runoff. In order to reduce the nitrogen losses in this watershed, higher straw returning amount (1.5 kg/m²) and coarse grain straw (5 cm) was recommended. Small or compost with no urea also could be applied according to different growth periods of flue-cured tobacco absorption and soil nutrient conditions.