Soil Quality Degradation Characteristics And Mechanism Of Orchard Soil In Weibei Region

Weibei is one of the most suitable area for planting apple trees in Shaanxi province. The natural environment and appropriate soil texture such as the high attitude, sufficient illumination, big temperature difference, suitable p H, high organic matter in this area is best for growing apple trees. Apple production contributes greatly to the economic development of Shaanxi province. But orchard soil has degraded significantly after years of fruit production, which lead to tree senescence and various diseases such as apple bitter pit, water-core, valsa canker and leaf defoliation diseases. As a result, fruit yield and quality decreased sharply.The objective of this study was to investigate the characteristics, mechanism and degree of soil physical and calcium degradation in different aged orchards, to provide scientific basis for orchard soil management and eventually to improve the yield and quality of apple production.Four replicates of <10-, 10-20- and >20-year old orchards soil and farmland soil as control were selected for the study in Binxian, semiarid region of Shaanxi. Samples were taken within two-thirds of the radius of the tree canopy. Soil samples were used to measure physical and chemical properties such as soil bulk density, compaction, porosity, saturated hydraulic conductivity, clay content. pH, CaCO3, exchangeable Ca, water-soluble Ca. and get the following conclusions:1. The characteristics of the invisible soil physical degradation is obvious in Weibei region. Although orchard soil physical condition is good in 0~20 cm soil layer, but below 20 cm, The increased soil bulk density and compactness, reduced soil Porosity, decreased soil saturated hydraulic conductivity, etc., had invisible stealth characteristics.The study of different aged orchards(<10-, 10-20- and >20-year old) in the Weibei Region showed that soil bulk density and compaction increased with orchard age and soil depth increased. Especially below 20 cm soil layer, soil bulk density reached 1.45–1.61 g/cm3, compaction reached 933–2433 KPa. Porosity of the soil profile in 0~20 cm soil layer remained 50%, and the soil structure was in good condition. However, soil porosity reached 40%–46% in the 20~60 cm soil layer, which was in a state of compaction and severe compaction. Soil saturated hydraulic conductivity decreased even in the surface layer as the orchard aged. In the 10-20 and >20-year-old orchards, soil saturated hydraulic conductivity in the subsurface declined to 46.88 and 20.89 cm/d, reducing the infiltration of the rainfall and the capacity of soil water storage. Using packing density as index to evaluate the degree of compaction in orchard soil, the result showed that the soil packing density of orchards was above 1.40 g/cm3 underneath 20 cm depth in Weibei region. The orchard soils in this area have reached the moderate degree of compaction.2. The decreased soil organic matter content and obvioused deposition argillic process as orchard age increased, became the reasons of soil compaction in the subsurface layer.The organic carbon density in orchard soil were higher in comparison with the farmland soil, but soil organic carbon density in 0~40 cm soil layer significantly decreased with the soil depth and planting ags increased. Soil clay content increased with the depth of soil profile. Clay content in the 0~30 cm depth decreased with increasing orchard age, but increased below the 30 cm layer.Further analysis found that the clay content had significantly correlated with soil bulk density, compactness, and porosity. The main processes and mechanism of orchard soil degradation are clay translocation and accumulation of clay at soil surface. Reduced plow and aeration on soils is the main external cause to anabatic dominanted soil degradation. This is reflected with less soil aggregates.3. Orchard soil Ca degrades significantly, affecting the health and resistance of fruit trees and the fruit quality.The soil CaCO3 content and storage in 0~50 cm increased as orchard age increased, while decreased as orchard age increased in 50~100 cm. And soil CaCO3 storage in the orchards older than 10 years were significantly lower than that of farmland in 0~50 cm. The exchangeable Ca and water-soluble Ca in all orchards soil were higher in comparison with the farmland soil. And the orchard soil exchangeable Ca decreased with orchard age increasing in layers of 0~40 cm and below 60 cm, while slightly increased with orchard age increasing in 40~60 cm. The water-soluble Ca content and storage in 0~50 cm were higher than that in 50~100 cm, and the soil water-soluble Ca has a peak in 10~30 cm in the orchards older than 10 years. The storage of soil CaCO3 and exchangeable Ca in the layer of 0~100 cm decreased severely with orchards planting years increased, even in the calcareous soil of loess dry-land in Shannxi Weibei Region. Which has become one of the characteristics of soil degradation. Calcium deficiency should be concerned in the orchard fertilization management in this region.4. For obvious internal compaction problem in Weibei orchards, through "blank" technical measures to the orchard soil, can increased the air permeability of soil and water infiltration and corrected the shortage problem of soil inside moisture. Through different materials of landfill treatments, the treatments had significantly different effect on soil CO2 emission flux, and soil CO2 emission flux have obvious relationship with soil moisture content, Too wet or too dry can affect the soil CO2 release.