Impact Of Land Use Models On Soil Erosion In Red Soil Hilly Area In Southern China

Soil erosion by water is a major problem threatening agricultural development in southern China, large areas of which are hilly and mountainous. It is one of the key factors that will reduce the capacity of soil ,which supports the increase in agricultural production needed to feed the growing population in this region. Researches on soil erosion and soil loss controlling in this area were well documented. However, in the past research, there has often been inadequate understanding the rule of soil erosion by systems approach and soil erosion management from agroecosystem approaches has also been neglected. To identify the ecological factors influencing soil and water lose and to find out ecological rule of soil erosion, I conducted this research on 31 farming systems at two experiment sites within red soil hilly area during 2002-2005. The major results are as follows: 1 Fanning systems and soil erosion (1) Characteristics of soil erosion under different farming systemsBasing on the farming activities, the 31 farming systems, distributing in different slope land (details in chapter 2) , were grouped into 4 groups, i.e. pure forest systems, agroforest system, cropping systems and cropping systems + terrace. At the site that the slope was greater than 15°, the amount of soil erosion occurred in cropping systems was significantly higher than that in other systems, following the order: agroforest systems > cropping systems + terrace > pure forest systems. At sites that the slope was between 10-15°, therewas no significant difference of soil erosion between forest systems and cropping systems + terrace, between agroforest systems and cropping system, but the amount of soil erosion was significant higher in cropping systems and agroforest systems than that in forest systems and cropping systems + terrace. At sites that slope was less than 10, no significant difference was found among these four groups of farming systems.(2) Changes of soil erosion during the farming system developmentThe dynamics of soil erosion among the four groups of farming systems (forest systems, agroforest systems, cropping systems and cropping systems + terrace) was significant different. For cropping systems and cropping systems + terrace, which farming activities were presented around year and every year, the amount of soil erosion kept higher during the farming system development. For forest systems and agroforest systems, soil erosion was higher in early stage of farming system development, but soil erosion decreased rapidly and kept steady state in the late stage. Data from two farming systems at watershed scale also showed that soil erosion was serious in the early stage of development and then decreased.(3) Farming systems with different plant communities and soil erosionSoil erosion significant differed in farming systems with different plant communities. At the similar soil and slope situation, soil erosion was lower in the farming system with multiple plant canopy than that in the farming systems with single canopy. Farming systems with species diversified communities significantly decreased soil erosion compared to that with single species.(4) Soil erosion occurring around a year and farming systemsSoil erosion occurring around a year differed among farming systems. For cropping systems and cropping systems +terrace, soil erosion occurred major in March and June when was rainy season and sowing, tillage and weeding were conducted. For forest systems and agroforest systems, soil erosion only occurred in June when was rainy season.Data from fanning systems at watershed scale also showed that there two stage that serious soil erosion occurred during a year.2 Soil loss tolerance(1) The amount of soil loss tolerance for red soil hilly area of southern China was calculated by nutrient balance, and different values of soil loss tolerance for this area were presented. At the case of no significant different among nitrogen, phosphors and patassium, and among farming system, value of soil loss tolerance for this area was 383.67 Tkm" .a"1. At case that there was different only among farming systems, value of soil loss tolerance was 35.07 Tkm~2.a"' and 61.82 Tkm^.a"1 (for ecological restoration). If only considering nutrient (N, P and K) balance soil loss tolerance were 36.84 Tkm'2.a" and 23.59 Tkm'2.a"'(for ecological restoration). If considering the differences both among nutrients and farming systems, value of soil loss tolerance were 11 ^STkm^.a"1 and 2.75 Tkm"2.a"' (for ecological restoration).(2) The average value of soil loss tolerance was highest in the forest systems (422.00 Tkm"2.a"' and lowest in fallow (61.82 Tkm"2.a"',). This suggested that the forest system were the better land use patterns than the fallows by the view of soil loss tolerance.(3) Considering the value of soil loss tolerance varied because the calculating was based on nutrients and farming systems, it was necessary to reduce the difference by using average value to evaluate the value of soil loss tolerance. Results from this research suggested that the average value of soil loss tolerance was 383.67 Tkm" .a"1 for red soil hilly area of southern China. For the area of restoration, value of soil loss tolerance was 23.59 Tkm"2.a"', for utilizing area, value of soil loss tolerance 383.67 Tkm" .a"1, and for protection area, value of soil loss tolerance was 23.59 Tkm"2.a"'.3 Approaches to sustainable fanning systems based on soil conservationSustainable farming systems at watershed scale were studied by multi-objectives linear programming. Best approach was proposed after comparing the several scenarios. Underthis scenario, at watershed scale, the faming system will reduce soil erosion to 2.92 t/hm .a. At the same time economic output will be not decreases.Results from this research suggested that utilizing upland resource reasonably could control soil erosion and develop economy rapidly. For red soil hilly area, as most economic output was from economic forest, the better utilization was occupying area of forest systems was 43.17%, area of agroforest systems and farming systems was 30.04%and 4.22% respectively. Area ratio was economic forest: agroforest:farming land 9: 7: 4.