Soil Physical Quality Degradation Characteristics In The Guanzhong Farmland

Along with the adjustment of agricultural industrial structure and the decrease of cultivated land, land intensive management led to the farmland soil physical characteristic of “stealth degradation” process. Based on farmland soil utilization, management, objective reality in guanzhong plain, and the evolution trend of the soil physical quality, etc., in this study across the guanzhong basin and tableland in 11 counties within the scope of the farmland has carried on the investigation and study, analyzed step by step physical quality condition of 0 ~ 40 cm of the soil profile. To explore the inner mechanism of the degradation of soil physical quality, analysis ability to resist human disturbance and degradation of soil, from the soil particle composition, organic matter content and soil reunion condition and stability, etc., the results show that:1. The farmland soil physical degradation characteristics is a clear reference. Influenced by the surface layer of soil compaction, soil magnetism generally shallow. loose soil magnetism in 5~21cm thickness changes. Within the scope of the investigation, good condition of soil magnetism in 20 cm the thickness is only 18%.The guanzhong irrigation and physical condition well arable layer average soil bulk density is 1.21 g/cm3; In about 20 ~ 40 cm soil layer, average soil bulk density in is 1.58 g/cm3, belongs to the very tight state. About 36% of soil bulk density met or exceeded that the limit of 1.60 g/cm3 density values.The arid topsoil layer average soil compactness is 373 kpa; From the top to down, compaction has the trend of first increases and then decrease, confirmed that the soil layer of dense state is restrict the sub surface soil compaction of the guanzhong farmland soil and not moisture content. Compacted soil prevented the extension of crop root system.The total porosity of sub surface is less than 50%, belonging to the dense state, and a majority of Guanzhong farmland soil sub surface belong to serious dense state, influence moisture transfer transport and crop drought resistance, lodging resistance.Saturated water rate of sub surface(20~40cm) is significantly smaller than that of the topsoil(0-10cm), after the continuous pilot water 120 min, saturated water rate reached the stable process basically, saturated water rate of soil topsoil by the beginning of 1.05mm/min decline to the 0.70mm/min, and tends to stable. Subsurface soils with low water permeability affects soil acceptance by rainfall and irrigation water. The soil calcium carbonate content less than subsurface, is about 10g/kg2. Based on the soil properties, the soil degradation resistance and mechanism are analyzed. The Guanzhong area of soil calcium carbonate, topsoil calcium carbonate content less than subsurface, is about 10g/kg, certain calcium carbonate in shallow eluviation and deposition, resulting in subsurface soil compaction degree increase.The difference of soil aggregate in the surface and sub surface layer in the Guanzhong area was large. 1~5mm "(mass) dominant aggregate" in the surface soil was 2.7 and 1.5 times of the sub surface layer under the dry and wet sieving. In 20~40cm soil layer, at the group aggregate stability is poorer, resulting in subsurface soil bulk density increase, compaction degree increase and topsoil layer of the main reasons.The organic matter content of soil in farmland of Guanzhong area compared with the sub surface, soil organic matter content decreased by 40%, topsoil and subsurface soil organic matter content showed significant differences, and affecting soil physical state.3. Evaluation of soil physical degradation in Guanzhong area. Guanzhong farmland topsoil soil compaction and density is less than 1.40g/cm3, belong to a low degree of compaction, and subsurface soil compaction has reached moderate compaction. Guanzhong farmland soil aggregate did not reach the quality standard of quality aggregate state, surface soil Kctp is 0.76~1.10, belonging to medium quality; Subsurface soil Kctp is 0.31~0.77, a majority of region belongs to the medium quality and other areas belong to the bad state of the aggregates. Guanzhong farmland soil aggregates is relatively good, subsurface soil aggregates is poor quality level state, become the soil compaction of the root causes. Topsoil soil silt and clay content is less than the compaction of the subsurface, and fine sand and coarse sand is higher than the content of the compacted layer, drench the soil clay, in the sub surface deposition, soil pore blockage, lower soil bulk density becomes larger, compactness increases, saturated hydraulic conductivity decreased etc..