The Processes Of Water And Nutrients And Their Biological Response In Sandy Soil Amended With Pisha Sandstone

As an important coal and energy base in China, the contiguous areas of Shanxi, Shaanxi and Inner Mongolia has widely distributed Pisha sandstone. Sandy soil is the major type of soil in the area. In addition, the area is also a major source of Yellow Rive grit. Considering damaged ecological environment due to coal mining, soil and water losses as well as low fertility of sandy soil, this study was designed to improve sandy soil by using Pisha sandstone so as to achieve the goal of reducing soil and water losses and improving Sandy soil’s capacity of preserving moisture and fertility. Through lab simulation experiment and model simulation study, the article discusses the hydraulic property of amended sandy soil（amended soil for short）, and its adsorption and desorption of nitrogen（N） and phosphorus（P）, thereby determining the best proportion of Pisha sandstone. We analyzed nutrient availability of amended soil and its plant response by using soil column culture experiment and pot experiment. We explored the water and fertilizer management mode which is suitable for rock-soil and evaluated the effect of using Pisha sandstone to improve sandy soil in the light of the soil-vegetable system. The main results are presented as follows:（1）Pisha sandstone can significantly reduce the water infiltration rate and saturated hydraulic conductivity of amended soil. The rate of decrease enlarges as the proportion of Pisha sandstone increases. Pisha sandstone can also increase the saturate water content and residual water content, and improve the capacity of sandy soil to retain water. When the proportion of Pisha sandstone reaches 25%, the saturated hydraulic conductivity and the water infiltration rate of amended soil would slow down, which is conducive to water retention on the upper layer of soil. The VGM（m, n） model can simulate the water characteristic curve of soil amended by Pisha sandstone and sandy soil.（2） As the proportion of Pisha sandstone increases, the adsorption and desorption of ammonium nitrogen（NH₄⁺-N） in amended soil also present an upward trend. Pisha sandstone could improve the fertilizer and supply of fertilizer significantly in sandy soil. The adsorption of NH₄⁺-N in amended soil included two processes: physical adsorption and chemisorption. These kinds of adsorption belong to a spontaneous exothermic reaction. Pseudo-second order kinetic model could simulate the adsorption kinetics of NH₄⁺-N in amended soil, while the Freundlich model could simulate the process of isothermal adsorption of NH₄⁺-N in amended soil.（3） Pisha sandstone could reduce P adsorption while increasing P desorption and supply of soil phosphorus in sandy soil. The adsorption of P in amended soil included two reactions: chemisorption and ion exchange-based adsorption; and these kinds of reaction were spontaneous endothermic reaction. Pseudo-second-order kinetic model was the best model to simulate the kinetics adsorption of P in amended soil. The Langmuir model was the best model to simulate the endothermic reaction process in amended soil.（4） Sufficient water conditions could enhance the content of nitrate nitrogen（NO₃^--N） and available P（AP） in amended soil. Pisha sandstone could enhance the content of NH₄⁺-N but reduce the content of NO₃^--N and AP in amended soil.（5） Under appropriate conditions of water and fertilizer, the ryegrass biomass in amended soil could be accumulated and the amount of N and P adsorbed by ryegrass could be increased by adding Pisha sandstone. Pisha sandstone could accelerate the formation of aggregates which is greater than 0.25 mm in amended soil and thus enhance the mechanical stability of the aggregates.This study would provide scientific evidence for the feasibility of using Pisha sandstone to improve sandy soil, offer a new sight for regional ecological restoration and soil erosion control, and also open up a new way for the application of Pisha sandstone in agricultural production and ecological restoration.