| Black soil is the most valuable land resource and has the reputation of“treasure in the earth”.It has the characteristics of high fertility,good structure,suitable for crop growth.As one of the four black soil regions in the world,the northeast black soil region plays an irreplaceable role in safeguarding regional ecological and environmental security,national food security and sustainable agricultural development.However,due to the high-intensity utilization of black soil resources over the years,the natural fertility of black land has been declining year by year,the black soil has been seriously degraded,and the black soil layer has become thinner.Strengthened the black protection and management of land is an urgent task.In addition,Heilongjiang Province is rich in straw resources,but the comprehensive utilization rate is only about 33%.At the same time,the effective utilization rate of agricultural water is low,which seriously restricts the sustainable development of local agriculture.The preparation of biochar based on crop straw can not only reduce the pollution of the atmosphere such as straw burning,but also improve the soil structure,increase soil water holding capacity and increase crop yield.Based on the above background,this paper conducted a four-year experiment at the Heilongjiang Institute of Hydraulic Research.After the application of biochar in the typical slope runoff area in 2016,biochar was no longer applied.The post-effects on soil physical and chemical properties and soil hydrodynamic parameters within 4 years after single application of biochar from 2016 to 2019 were analyzed by indoor and outdoor experiments.Numerical simulation of soil water movement and solute transport using HYDRUS software was carried out.The effect of soil water movement and solute transport on slope farmland in black soil area within 4 years after single application of biochar was clarified.The main conclusions are as follows:(1)The results of the after-effects of biochar on the physical and chemical properties of the soil indicate that within 4 years of a single application of biochar,the soil bulk density is significantly reduced,the soil porosity,saturated moisture content and field water capacity are increased,making the soil structure loose and mature increasing the degree,enhancing the permeability,and improving the water holding performance,so that water and nutrients can be more easily transported to the crop root system,and promote crop growth and development.However,with the increase of the age and slope after the application of biochar,the decrease in soil bulk density,increase in soil porosity,and increase in soil water holding capacity all showed a significant decrease.After the application of biochar,the soil p H,organic matter,ammonium nitrogen and available potassium content that characterize fertility can be significantly increased after the application of biochar(P<0.05),increase soil nutrient levels,increase soil fertility,and promote the increase of soybean yield.The maximum growth rates of soil organic matter,ammonium nitrogen,and available potassium are 18.21%,27.23%,and 20.31%,respectively.The change law of indicators is similar.The factor of whether or not to apply biochar has the most significant impact on the properties of the soil and has the strongest explanatory power.The degree of influence of the year and slope factors on each index are different,but they are not as great as those of biochar.The result shows that the impact degree of biochar on each index was the most significant in the year,and the biochar was still effective for three years from 2017 to 2019.(2)The results of the after-effects of biochar on soil hydrodynamic parameters show that the Van Genuchten model is used to fit the soil water characteristic curve for 4 years,and it is found that the model has a good fitting effect on each treatment.Biochar has an increasing effect on both?_s and?,and a decreasing effect on both?_r and n.Within 4 years after a single application of biochar,soil moisture content can increase,SWCC moves up,specific water capacity increases,and soil water-holding and water-supplying capacity is improved.It prolongs and weakens year by year,and increases with the increase of slope.Within 4 years after carbon application,K(h),D(?)and Ds(?)all increase with the increase of?.K(h)??has a good power function relationship.D(?)and Dsh(?)has a clear exponential relationship.2016 to 2019 can increase the unsaturated soil hydraulic conductivity K(h),can promote the wet peak forward speed,significantly increase the Boltzmann transformation parameter?,and with the extension of the time after the application of biochar to K(h)The increase of?decreases year by year.When?<0.42 cm~3/cm~3,biochar inhibits the diffusion of soil moisture in the horizontal direction,when?>0.42 cm~3/cm~3,biochar promotes the horizontal diffusion of soil moisture.When?<0.36 cm~3/cm~3,biochar can inhibit the dispersion of Na Cl solution in soil,when?>0.36 cm~3/cm~3,biochar can promote the dispersion of Na Cl solution in soil.The test area?is in the range of 0.20?0.35 cm~3/cm~3.Therefore,the biochar has an inhibitory effect on water diffusion and Na Cl solution dispersion,and the biochar has an inhibitory effect on water diffusion and solution dispersion as the slope increases and the age after carbon application prolongs.D(?)and Dsh(?)were significantly positively correlated with soil bulk density,and significantly negatively correlated with porosity and organic matter content.At the same time,D(?)and Dsh(?)had a significant positive correlation.(3)Results of numerical simulation of biochar on soil water movement and solute transport:based on the theory of soil hydrodynamics and SPAC,the basic equations in HYDRUS-1D software are used in combination with the experimental area to establish a model of unsaturated soil water movement and solute transport for the simulation of soil moisture content and soil solute content after rain is in good agreement with high accuracy of the simulation results.The model shows strong applicability and can be used to simulate the soil wa ter movement and solute transport process in this area.It can be seen from the simulation results of the model that only a single application of biochar to the test soil in 2016 has an increasing effect on the soil moisture content and soil solute content of 48 h after rain within 4 years,and the maximum growth rates were 10.24%and 24.11%,respectively.After the rain,the soil water retention and solute retention effect will keep more water and nutrients in the soil,so that the optimization of the crop growth environment is more conducive to crop growth.Each year,the effect on soil water retention and retention after rain has no obvious relationship with slope,and the effect of increasing soil solute content after rain increases with the increase of slope. |
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