Impacts and mechanism of Eulaliopsis binata hedgerow system on soil and water losses control in purple hilly area in Sichuan basin.

The purple hilly area of Sichuan basin,located in the upper reach of the Yangtze River,is one of the most severe soil erosion in China,where three quarters of its land surface are seriously affected by soil erosion and the average erosion rate can reach 3200-7900 t/km2/a.This area is the most important agricultural section of Sichuan province and Chongqing municipal.Extensively cultivation,dense population and heavy soil and water losses is not only a severe environmental problem but also an obstacle to agricultural sustainable development.To improve soil erosion environment,reduce soil and water losses using hedgerow system is one of the most important issues in over-farming land and ecological fragile area.Eulaliopsis binata(Retz.)G.E.Hubb has abundant roots and high yield,and the time when Eulaliopsis binata(Retz.)G.E.Hubb growths fast is as the same as the time of the rainy season in this area,so Eulaliopsis binata(Retz.)G.E.hubb can mulch soil surface well and reduce soil and water losses significantly.The total length of roots in a 120 cm wide and 90 cm deep soil profile is 98714.8cm,which can enlace soil about 235 circles.The average diameter of Eulaliopsis binata(Retz.)G.E.Hubb root is from 0.20 mm to 0.50 mm,and 95% roots,diameter is thinner than 0.40 mm.The total surface areas of roots is 10139.68 cm2,and the surface areas of roots is about 2 to 3 times to soil surface areas in the surface layer.Enlacing and concretion to soil profile of Eulaliopsis binata(Retz.)G.E.Hubb root and the gigantic adsorption to soil grains of root surface are the mechanism why Eulaliopsis binata(Retz.)G.E.Hubb can reduce soil and water loss significantly.The monitoring result from 2003 to 2004 indicates that,when the gradient is 12 degrees,the runoff rate of planting Eulaliopsis binata(Retz.)G.E.Hubb completely after changing slope land to ladder(PECC,so as the follows) is only 49.90 m3/hm2·yr.and the soil loss rate is 155.78 kg/hm2·yr,however,the runoff rate of farming and being not change slope land to ladder(FNC,so as the follows) is 314.29 m3/hm2·yr that is 6.30 times to PECC,and the soil loss rate is 3322.50 that is 21.33 times to PECC;When the gradient is 24 degrees,the runoff rate of planting eulaliopsis binata(Retz.)G.E.Hubb in the ridge and border slope land after changing slope land to ladder(PERBC,so as the follows) is 248.04 m3/hm2·yr and the soil loss rate is 612.00 kg/hm2·yr,the runoff rate of PECC is only 42.44 m3/hm2·yr and the soil loss rate is 153.75 kg/hm2·yr,however,the runoff rate of FNC reaches to 785.73 m3/hm2·yr that is 3.17 times to PERBC and 18.52 times to PECC,and the soil loss rate reaches to 37503 m3/hm2·yr that is 61.33 times to PERBC and 244.12 times to PECC.