The Effect Of Different Terrace-protecting Plants On The Physicochemical Property And Soil And Water Conservation Of Terrace Bio-banks

Middle part hilly area of Sichuan province, as typical hilly area in China, there is Mesozoic purple sandstone and mudstone with crunchy texture, which is highly vulnerable to erosion and weathering, resulting in serious soil erosion, what’s more, the problem in the hilly area of cropland is the most prominent. How to solve the soil loss problem has become an important research topic. The terrace bio-banks is a kind of agroforestry systems, which can control soil and water erosion, improve ecological environment of farmland, raise biological production and economic capacity of per unit area. Meanwhile, the terrace bio-banks raise land utilization rate and ameliorate the structure of the soil in sloping and nutrients, which provides a better reference and basis for the comprehensive utilization of mountain hil y area of land.The study was in the area of Huxi small watershed in Shehong County in Sichuan province. The overall objective of the project was to study the effect of soil and water conservation of four different terrace bio-banks, including the daylily, alfalfa, tall fescue and radix ophiopogonis terrace bio-banks, and the blank terrace bio-bank worked as the control group. What’s more, every type of terrace bio-banks set up 3 similar slopes as replications, and every slope set up 3 replications again. Through field investigation and laboratory experiments, the soil structure of different terrace bio-banks of different slope locations（top, middle and bottom of slope） and soil layers(0-5cm soil layer with artificial covering earth and 5^-10 cm soil layer of mother rock) were analyzed, for specific performance, soil bulk density, soil p H, mother rock, water storage conditions, fractal dimension characteristics of mechanical composition and soil aggregates, soil infiltration characteristics, soil cohesion and angle of internal friction and other indicators of the different terrace bio-banks were compared. The study results could provide evidences for the further improvement and popularization of grid terrace bio-banks. And the main study results as follows:1) The average values of soil bulk density of plant terrace bio-banks were 1.34¹.58 g·cm-3, while that of the control group were 1.58¹.65 g·cm-3 so that the soil bulk density values of the control group were larger than that of plant terra ce bio-banks, and the minimum values of that were tall fescue and radix ophiopogonis terrace bio-banks. The soil bulk density of plant terrace bio-banks showed the top< the middle< the bottom of the terrace bio-banks slope surface, but the control group showed an inverse pattern. The soil bulk density average values of 0-5cm soil layer were lower than that of 5^-10 cm. The average values p H of plant terrace bio-banks were 7.197⁸.200, while that of the control group were 8.204⁸.274 so that plant terrace bio-banks were beneficial to adjusting p H of soil. Before rainy season, the slope position was the influence factor to p H of soil of terrace bio-banks, while the soil layer was the influence factor to plant terrace bio-banks. After rainy season, both the slope position and soil layer were the influence factors to plant terrace bio-banks. The average values of organic content of plant terrace bio-banks were 3.31²0.73 g·kg^-1, while that of the control group were 1.18⁵.08g·kg^-1. It was observed that the organic content of plant terrace bio-banks was higher than that of the control group. After rainy season, organic content of all the terrace bio-banks decreased, and the control group showed greatest change.2) The distribution regularity of slope surface of the maximum amount of soil moisture retention reservoir, maximum soil moisture retention water storage and saturated soil moisture water storage of plant terrace bio-banks showed the top> the middle> the bottom of the terrace bio-banks slope surface, while the control group showed an inverse pattern. The water storage parameters of soil of terrace bio-banks after rainy season were lower than that before rainy season, and the effect of rainy season on daylily terrace bio-banks was most conspicuous. On the whole, the water storage properties of alfalfa, tall fescue and radix ophiopogonis were better performance. Before rainy season, slope location and soil layer had no significant influence on the maximum amount of soil moisture retention reservoir of alfalfa, tall fescue and radix ophiopogonis terrace bio-banks, but had significant influence on that of daylily and the control group. The slope location and soil layer had significant influence on the maximum soil moisture retention water storage of the control group, and soil layer had significant influence on that of the plant terrace bio-banks. The soil layer had significant influence on the saturated soil moisture water storage, while the influence of slope location depended on the vegetation type of terrace bio-banks, what’s more, the vegetation type of terrace bio-banks were the factors to the saturated soil moisture water storage. After rainy season, slope location had significant influence on the maximum amount of soil moisture retention reservoir of alfalfa and the control group. The soil layer had significant influence on the maximum soil moisture retention water storage. The soil layer, slope location and the vegetation type were the factors to saturated soil moisture water storage. The soil infiltration parameters showed the initial infiltration rate> the average infiltration rate> stable infiltration rate. The distribution regularity of slope surface of the soil infiltration parameters showed the top> the middle> the bottom of the terrace bio-banks slope surface, while the control group showed an inverse pattern. The soil infiltration parameters decreased 37.57%⁹1.79% after rainy season. To sum up, before rainy season, the improvement of soil permeability of plant terrace bio-banks showed tall fescue> radix ophiopogonis> daylily.3) Research on the soil mechanical composition of different terrace bio-banks the showed that before rainy season, the content of coarse sand and fine sand of plant terrace bio-banks was lower 16.86%⁷5.16% than that of the control group, and the content of clay increased 7.79%³1.55%; after rainy season, the content of crude clay of plant terrace bio-banks increased 46.94%⁹5.05% than that of the control group; the improvement effect of different plant terrace bio-banks on soil texture was different. Research on the soil micro-aggregates of different terrace bio-banks the showed that before rainy season, the content of coarse sand of plant terrace bio-banks was lower 5.25%⁸0.90% than that of the control group; after rainy season, the content of coarse sand decreased; the effect of rainy season was decreasing coarse sand and increasing coarse silt. The distribution regularity of slope surface of mechanical composition of soil fractal dimension of plant terrace bio-banks showed the top> the middle> the bottom of the terrace bio-banks slope surface, while the control group showed an inverse pattern. Before rainy season, the mechanical composition of soil fractal dimension of terrace bio-banks showed alfalfa（2.7238）> daylily（2.7000）> rad ix ophiopogonis（2.6699）> tall fescue（2.6696）> the control group（2.6690）, while after rainy season showed that daylily（2.6666）> alfalfa（2.6607）> radix ophiopogonis（2.66383）> the control group（2.60688）> tall fescue（2.5714）. Before rainy season, the mechanical composition of soil fractal dimension values of 0-5cm soil layer were less than that of 5^-10 cm soil layer, while after rainy season showed instead law. The distribution regularity of slope surface of soil micro-aggregates fractal dimension showed the top< the middle< the bottom of the terrace bio-banks slope surface, while the control group showed an inverse pattern. Before rainy season, the soil micro-aggregates fractal dimension of terrace bio-banks showed radix ophiopogonis（2.5838）> the control group（2.5486） > daylily（2.5407） > tall fescue（2.5047） >alfalfa（2.4852）, while after rainy season showed that radix ophiopogonis（2.6160）>daylily（2.6017）> the control group（2.5786） > tall fescue（2.5685）>alfalfa（2.5425）. The soil micro-aggregates fractal dimension of terrace bio-banks after rainy season increased 1.25%, 2.40%, 1.18%, 2.55%, 2.30% than that before rainy season.4) Before rainy season, the average values of soil cohesion of different terrace bio-banks showed daylily（37.49 kpa）> alfalfa（34.00 kpa） >tall fescue（28.85 kpa）>radix ophiopogonis（22.50 kpa）> the control group（20.31 kpa）, while after rainy season showed alfalfa（29.81 kpa） >daylily（19.81 kpa）> tall fescue（13.55 kpa）>radix ophiopogonis（11.73 kpa）> the control group（11.25 kpa）, and the average values of soil cohesion after rainy season decreased 12.33%⁵3.02%. The soil cohesion average values of 0-5cm soil layer were lower than that of 5^-10 cm. The distribution regularity of slope surface of soil cohesion of daylily, tall fescue and the control group terrace bio-banks and the 0-5cm soil layer of radix ophiopogonis showed the top< the middle< the bottom of the terrace bio-banks slope surface, while the control group showed an inverse pattern, while that of alfalfa terrace b io-banks and the 5^-10 cm soil layer of radix ophiopogonis showed the top> the middle> the bottom of the terrace bio-banks slope surface. Before rainy season, the average values of soil friction angle of different terrace bio-banks showed tall fescue（27.69°）> daylily（27.04°） >alfalfa（26.18°）> radix ophiopogonis（24.18°） > the control group（20.88°）, while after rainy season showed radix ophiopogonis（22.66°） > tall fescue（22.07°）>daylily（21.82°） > alfalfa（18.64°）> the control group（17.56°）. The soil friction angle average values of 0-5cm soil layer were lower than that of 5^-10 cm. The distribution regularity of slope surface of soil friction angle of terrace bio-banks was different.