The Variation Of Soil Quality And The Sustainable Utilization Of Hilly Dryland In The East Of Great Xingan Mountains

Based on the method of quantitative and qualitative analysis, this study was conducted to investigate the change of soil fertility characteristics, soil physical properties, soil environmental quality, soil erosion status of hilly dryland in the east of Great Xingan Mountains, and then the reasons for those changes were comprehensively investigated. At last, the technical and strategically pathways were put forward for sustainable utilization and agricultural sustainable developmental model in this area. The results were list as follows:(1) Compared with the parameters at 20 years ago in the studied regions, the soil organic matter content decreased 23.8%, soil total nitrogen content decreased 31.9%., alkali-hydrolysable nitrogen content decreased more than 12%, and soil available potassium decreased 24.7%. Soil medium elements and microelements remain consistently, such as exchangeable calcium, exchangeable magnesium, available sulfur, available silica and zinc, copper, iron, manganese, while 87.2% and 78.2% of the soils were short of boron and molybdenum, respectively.(2) The soil physical properties had a trend of depravation in the recent 20 years in the studied area, which representing in the decrease of soil structure quality, the increase of soil bulk density, the decline of humus and availability soil layer, the form of obstacle layers and the increase of surface gravel contents. Secondary soil obstacle layers were formed in the studied 20 years, which resulted in a surface gravel layer and a 5~10cm hard ploughpans. The surface areas with gravel contents≥5% were increased by 20 times compared with 20 years ago. One third to half of the farmland were distributed in thin dark-brown soil, which has thinner humus layer (<20cm) and higher gravel content (>30%) and the gravel appeared under ground 20cm in general. With the increasing of the slope and cultivation years, the gravel content in soil surface increased significantly.(3) The integration pollution index of soil in studied areas were below 0.7 in general, which reached to theⅠclass standard, belonging to soil standard for green food production. Due to the different of natural factors and soil parent material and soil pedogenesis process, soil heavy metals such as mercury, chromium, arsenic, lead, copper contents in different types of soils had certain differences while soil cadmium contents had no such obvious difference. Soil pH values in the areas were on the average of 6.0, between 4.8~7.1, was slightly acidic to neutral response. The water quality from river and ground had reached the limits of quality standards for irrigation in the studied areas, which accorded to the water quality standards use for green food production.(4) In term of the national divisions of soil erosion type, the studied areas belonged to north-eastern hilly areas of black soil zone. There were different degrees of erosion, which mainly fall into two categories including water erosion and freeze-thaw erosion. Water erosion accounted for 99.8% of arableland erosion in this area. Freeze-thaw erosion only accounted for part of areas which called "land split" (2~5cm in width, 5~50cm in depth ) in the near Great Xingan Mountains forest due to the formation of frozen-thawed 20 years ago, while the area enlarged to 3.3 times more than before. The soil erosion intensity of arableland turned to micro-developed from mild. The soil erosion area above second class increased from 12.2×104 hm2 to 52.7×104 hm2, which increasing 4.3 times; The average soil erosion modulus were increased by 1935.7 t/km2/year from less than 500 t/km2/year. Gully density were increased by 1.87 km/km2 from 0.06 km/km2; 30% of the arableland has been subjected to serious soil erosion. The total thickness of soil loss for the 3~16.8cm, with an average of 8.4cm, an average annual loss of thickness 0.2~1.1cm, serious areas of individual annual soil loss amounted to more than 5cm since the reclamation of land, in which 11.3cm thickness soil layer was loss in dark brown soil, accounting for 51.3% of humus layer; 9.5cm thickness soil was loss in black soil, accounting for 28.8%of humus layer thickness; 4.4cm thickness soil was loss in meadow soil, accounting for humus layer thickness by 6.2% of the same soil type. In terms of the classification standards of the degree of soil erosion, black soil layer thickness accounts for 6.2% level of Class A, which is mild erosion; dark brown soil erosion accounts for 51.8% of A level, which is moderate erosion; meadow soil erosion thickness accounted for 4.4% of A level, which is slightly eroded. The overall erosion of the study area is a thickness of 8.4cm, accounting for 17.8% of A level, with a degree of slight erosion. Investigation of the studies showed that soil erosion resulted in, both deterioration of physical properties and nutrient loss. Average annual soil loss of the total amount is 9,167,000 t. The loss of organic matter reached 425,000 t. The loss of N, P, K nutrients equivalent to 59,000 t compound fertilizers with 40% content, 1.4 times of the total amount of chemical fertilizer use in this areas.(5) The soil particles <0.01mm content, porosity, aggregate content, field capacity decreased with the increase of slope, while bulk density increased with the slope. Soil pH value, organic matter, total nitrogen, available phosphorus, available potassium and effective copper, effective manganese, boron, silicon decreased with the increasing of slope, while soil available iron, molybdenum and efficient sulfur content increased with the slope. The seasonal uneven precipitation and evaporation increasing resulted in the worse of soil erosion; The temperature change and the increase of the frequency of severe weather also led to the degradation of arableland. Unreasonable cultivation, the small four-wheel tractor tillage system, and unscientific fertilization system, as well as the negative effects result from population growth and economic and social development were all led the degradation of soil quality.(6) Based on the analysis of natural and human activity factors which affected soil quality, the technical methods to sustainable utilization of cultivated land resources including district improvement, rational distribution, preventing soil erosion, rational fertility fertilization, reforming the faming systems were proposed. In addition, we also put forward corresponding strategic step such as enhancing legislative work to protect arable land, establishing the monitoring mechanisms for the conservation of farmland development of study area, and put the eco-environment restoration of farmland into the agenda of government, the establishment of Great Xingan Mountains green resources conservation areas, and developing the characteristics economic of the studied area. Finally, regional agriculture sustainable development patterns in the studied area were proposed.