| The black soil region in Northeast China is the main grain production area and commodity grain base of China. In recent years, soil erosion has become more and more serious, which greatly affects regional food production and food security of our country. Therefore, revealing the effects of soil erosion-deposition on soil quality and crop yield in the black soil area had become more important for protecting the valuable black soil and guarantee food security of China. This dissertation took Dongshangou watershed, located at Songhua River Basin of typical eroded black soil area of Northeast China, as a research area site. According to field investigation combining with laboratory analysis, mathematical statistical analysis, radioisotope tracer and GIS technology, the dissertation analyzed the spatial distribution characteristics of soil erosion-deposition, studied the influence of soil erosion-deposition on soil physical, chemical and biological characteristics, determined soil quality assessment indicators under erosion environment and established evaluation model, and then explored the effect of soil erosion-deposition and soil quality on maize yield. The main results were as follows:(1) Spatial distribution characteristics of soil erosion-deposition were studied. The results showed that soil erosion rate in the watershed was ordered as follows upperstream>downstream> middle. Soil erosion was dominated in upper stream area, erosion and deposition was coexisted in middle reaches area, soil deposition was dominated in downstream area. Erosion rate along slope length followed as:middle slope position> crest position> upper slope position> lower slope position.(2) The distribution characteristics of soil water-stable aggregate ability and broken mechanism were analyzed. Results showed that aggregate breakdown in black soil was mainly caused by the compression of air entrapped inside aggregates, the second was clay swelling during wetting. The soil aggregate stability of plough layer was fluctuated along the slope surface.Then the effects of soil organic matter, clay particles content and reclamation duration on soil aggregate stability were analyzed.(3) Effects of soil erosion on soil nutrient, soil enzyme activities and microbial biomass C and N were studied. Results showed that spatial distribution of soil organic matter, total nitrogen, available nitrogen, available phosphorus, invertase, urease, alkaline phosphatase and microbial biomass C and N were significantly affected by erosion. In the mass, soil nutrient, soil enzyme activities and microbial biomass C and N was increased from upperstream to downstream in watershed and the variation tendency ordered as follows:higher(top-slope)-lower(up-slope)-low(mid-slope)-high(down-slope) along the slope surface. The relationship between soil erosion rate and soil organic matter, total nitrogen, invertase was highly significant negative correlation. Soil erosion rate had significant negative correlation with available nitrogen content, microbial biomass carbon and nitrogen content, and had negative correlation with urease and alkaline phosphatase. Thus, soil erosion is the important factor that can affect soil nutrient, soil enzyme activities and microbial biomass.(4) Soil quality assessment indicators were selected, and assessment model was established under erosion environment. Based on correlation analysis, sensitivity analysis, the dissertation chose MWDsw,>0.2mm soil water-stable aggregate,sand, soil organic matter, total nitrogen, available nitrogen, rapid available phosphorus, CEC, invertase, urease, alkaline phosphatase soil microbial biomass carbon and nitrogen as base indicators for soil quality evaluation. According to principal component analysis, the dissertation chose MWDsw,>0.2mm soil water-stable aggregate, soil organic matter, total nitrogen, available nitrogen, rapid available phosphorus, invertase and soil microbial biomass carbon as appropriate indicators for soil quality evaluation. According to discriminant analysis, soil invertase, organic matter, total nitrogen, available nitrogen and MWDsw were selected as key soil quality indicators and soil quality evaluation model which based on different index system was established. The calculation results of the soil quality index (SQI) showed that soil quality had degenerated seriously and stayed at low level in the study area. The distribution manifestation of soil quality is as follows:downstream of the watershed>middle reaches of the watershed>upstream of the watershed, and the variation tendency ordered as follows:middle-lower-low-high along slope length. SQI had highly significant negative correlation with soil erosion rate, which indicated the soil erosion intensity had important influence on spatial distribution of soil quality, and it was the most important and direct reason that led to soil quality impoverishment.(5) Effects of soil quality and soil erosion on maize yield were analyzed. Results showed that, maize yield was decreased from downstream to upstream, and the variation tendency ordered along slope length as follows:down-slope> top-slope> up-slope> mid-slope. Maize yield in soil erosion area were significantly lower than deposition area in the watershed, and it was mainly the middle-and-low-yield farmland in maize field. Maize yield had a highly significant positive correlation with soil quality. The results indicated that soil quality had a positive effect on the level and spatial distribution of maize yield.On the contrary, soil erosion had a negative effect on them. |
