Influence Mechanism Of Soil Thickness On Crop Growth In Purple Arable Land

Purple soil, characterized by fast physical weathering, rich mineral nutrition content, is an important type of farming soil in the Three Gorges Reservoir area.However, the trend of shallow purple soil not only hindered water storage, drought resistance, moisture and fertilizer retention, but also impeded the economic development of regional agriculture.The experimental plot was constructed with six different thicknesses of purple soil(70 cm, 60 cm, 50 cm, 40 cm, 30 cm, 20 cm) with chilli and lettuce as experimental crop. The experimental data obtained by using positional observation and sampling test.Analyzing time dynamic changes and profile distribution characteristics of soil moisture and soil nutrient, and also the influence on the growth of plant(pepper and lettuce) height, leaf area, biomass and yield, determining the influence factors of crop growth under different soil thicknesses by using multiple comparison test and path analysis.The results are as follows:(1) Under the circumstances of plentiful precipitation, all the six different kinds of soil thickness had higher moisture, and the value was between 22.58% ~ 24.41%. The profile of all the different soil thicknesses had higher moisture in the depth of 0 cm to30 cm, and the depth of 30 cm-70 cm had less precipitation recharge compared to the depths of 0cm to 30 cm.Under persistent drought conditions, the average soil moisture in the profile of the six different soil thicknesses was generally lower, and the value was 9.59% ~ 12.12%. The profile moisture displayed fluctuated trend within the depth increases, moreover, the thicknesses of 60 cm and 70 cm had obviously higher moisture than that of other shallow soil thicknesses. Six different soil thicknesses had positive correlation with soil surface moisture.(2) During the period of experiment crop growth, soil surface available N,available P, available K content in different soil thicknesses presented fluctuated trend,different nutrient elements in different month were also different. Available N,available P, available K in the profile of six soil thicknesses were mainly concentratedin the surface layer, moreover, the average nutrient content in profile of the six different soil thicknesses displayed downtrend. Soil thickness had positive correlation with the average soil surface nutrients.(3) The content of soil moisture and nutrient were great different in the condition of different soil thickness, and then the influence of crop growth and development was also great. The main factors affecting stem length under different soil thicknesses were soil moisture and available P, the thicker of the soil, the higher of element content, so the stem length growed higher, and also soil moisture occupied the main position,available P came to the second. The main factors affecting leaf area under different soil thicknesses were soil moisture, available N and available P, and the thicker of the soil,the higher of each element, so the leaf area growed larger, and available P occupied the main position, soil moisture and available N were decreasing in turn.The main factors affecting crop yield under different soil thicknesses were soil moisture, available N and available P, the thicker of the soil, the higher of each element, so the yield increased obviously, and soil moisture occupied the main position, available N and available P were decreasing in turn.(4) The thickness of 40 cm would be a critical thickness for vegetable crops on arable purple soil from the point of view that purple soil hinders water storage, drought resistance and the growth reaction(stem length, leaf area, biomass, yeild) of pepper and lettuce.