Effects Of Soil And Water Conservation Measures On Runoff And Sediment Reduction In Red Soil Slopes Of North Jiangxi

The research of water erosion on slopes has been priorities and hotspots at home and abroad. So far, lots of research work was carried on its regulation mechanism. While, most of the research results in China are about the water erosion in the Loess Area, and the targeted outcomes of other areas, such as the Southern Red Soil Area, are still relatively limited. To study the mechanism of different soil and water conservation measures affecting water erosion in red soil slopes in southern China, field experiments were performed on the representative area named Jiangxi Eco-science Park of Soil and Water Conservation(SWC), including sixteen runoff plots treated by different measures,i. e. forest and grass measures, agricultural cultivation measures, clean tillage in orchard, fruit terraced measures and bare control. The precipitation, surface runoff and soil loss of each treatment under each natural rainfall events were recorded from 2001-2009 and the physical soil properties and chemical soil properties were tested after 9 years. This research explores the effects of SWC measures on runoff and sediment yield, water and flood regulation and soil anti-erodibility in red soil sloping land which can provide a scientific refference for the optimization of SWC measures and sustainable development of ecological environment construction. The main results are as follows:(1) The rain process mostly happened in the rainy season(from April to September), so the runoff amount from the bare slope in the rainy season accounted for 86.3% of the average annual runoff loss, and the sediment yield from the bare slope in the rainy season accounted for 96.5% of the average annual soil loss. Thus, the rainy season is the key period to control and prevent soil and water loss. Under the conditions of national rainfall, the rainfall intensity was not stable and continuous, so the runoff process of the bare slope was also unstable and uncontinuous, with one or more peak values. The process of runoff and sediment under the same rainfall condition was the same in barren slope. The cumulative sediment yield and the cumulative runoff with time showed a slight growth at the first, then a rapid growth and a smooth change finally. Due to runoff yield under saturated storage, the relation of runoff with rainfall was higher than that with rainfall intensity. There existed linear regression between runoff and rainfall, rainfall energy, while there was power function regression between runoff and I30-Comparing to average rainfall intensity,â… -30 can better reflect the relation between soil erosion and rainfall intensity. There existed power function regressions between runoff andâ… 30, rainfall, rainfall energy and runoff amount.(2) These SWC measures can effectively reduce the amount of soil and water loss. Comparing to the control plot, the runoff of forest and grass measures (Citrus+grass) were reduced by more than 90% and the sediment were reduced by more than 99%. The runoff of agricultural cultivation measures were reduced by more than 65% and the sediment were reduced by more than 75%. The runoff reduction rates of clean tillage in orchard were above 33%, and its sediment reduction rates were above 58%. The runoff reduction rates of fruit terraced measures (Citrus+terrace) were above 70%, and their sediment reduction rates were above 89%. Among the Citrus+grass treatments, the benefits of water reduction was above 95% among grass full covered, grass stip covered and grass+crops stip covered, while their benefits of soil reduction rates were above 99%. Therefore, to reduce the cost and avoid species competition, grass or crops strip covered in orchard are suggested. Among the three species of Bahia grass, Broadleaf paspalum and Cynodon dactylon, their reduction benefits of runoff and sediment had no obvious difference. Therefore, the three grasses can all be applied to orchard with grass strip covered. Among strip intercropping in Citrus orchards, the cumulative SWC benefits of contour strip intercropping was better than that of downslope strip intercropping, and the former's SWC benefits were more outstanding under the special case of stroms. Therefore, contour strip intercropping to increase the coverage rate in new orchards is an effective measure to prevent soil erosion. As it is known, soil and water loss concentrated in the rainy season in this area. When planting intercropping crops, we should try to choose those their harvest and planting time aren't in the rainy season. On some special cases, the runoff and sediment reduction effects of clean tillage in Citrus orchard were significantly decreased even had more soil and water loss than that of the bare control. This can well explain that only tree layer without the coverage of litter, shrub or grass, is easy to cause the forest soil erosion phenomenon in South China. Among Citrus+terrace measures, SWC benefits of mound before and ditch behind on terrace platform, grass planting on the terrace wall, and inward inclined terrace were well, especially in the special case of storms. Thus, integrating these three individual technologies will obtain better SWC benefits, to enhance the erosion resistance of orchards to storms.(3) Reducing effects and lagging effects of runoff and its peak of several typical SWC measures, i.e. Citrus+Bahia grass full covered, Citrus+contour strip intercropping, clean tillage in Citrus orchard, Citrus+level terrace with mound before and ditch behind+grassed wall were analyzed. It was found that compared with the bare control, all these SWC measures had obvious benefits to reducing surface runoff amount and its peak values. Citrus+Bahia grass full covered had the greatest benefits, with 93.7% of runoff amount reduction rate and 99.1% of runoff peak reduction rate. While, clean tillage in Citrus orchard had the lowest benefits, with 53.8% of runoff amount reduction rate and 49.8% of runoff peak reduction rate. In addition to clean tillage in Citrus orchard, these three measures also have certain benefits to lagging runoff and its peak. Citrus+ Bahia grass full covered had the greatest benefits, with 93.3% of runoff lagging rate and 57.5% of runoff peak lagging rate. Clean tillage in young Citrus orchard hasn't the coverage of litter, shrub or grass, runoff is more sensitive to rainfall. So, its lagging time of runoff and its peaks were significantly shortened, even shorter than that of the bare control. Tor the same SWC measure, the benefit to reducing surface runoff amount and its peak valus was relatively stable. While, the benefit to lagging runoff and its peak was more unstabcle, mainly due to its multi-factors of rainfall (including early rainfall) and surface conditions.(4) Red-soil anti-erodibility was poor on barren slope in North of Jiangxi. Different SWC measures were applied to improve soil anti-erodibility. By grey correlation analysis of different anti-erodibility parameters on soil erosion modulus, it was shown that in the 10 anti-erodibility parameters, the first 2 factors affecting soil erosion modulus was soil agglomeration and soil erodibility index. The descending rank of the last 2 factors affecting sediment yield was EMWd and MWDC. The effects of soil particle dispersivity on sediment yield was better than that of stability of soil water-stable aggregates, their average grey correlation value were 0.618 and 0.599, respectively. Based on observed K factors of red soil in the study area, uncertainties of six K-factor prediction models(i-e-, nomogragh model, modified nomogragh model, EPIC model, two kind of geometricmean particlemodel, and Torri model) were evaluated. Results show that the six models were all high in uncertainty. Immeasurable error might result from direct indiscriminate use of these empirical models in estimating K factor. So, an optmized modified nomogragh model can minmize the uncertainty.