Numerical Simulation Of Soil Water Movement And Solute Transport Under Application Of Biochar In Black Soil Region

Northeast black soil is an important soil resource in China, and the black soil region is one of the most important commodities in grain production and export base, and grain production plays a crucial role in food safety of China. However, the average rainfall in the area for many years is uneven distribution, 80% of the annual rainfall distribution is in 7⁹ months and the rainfall intensity is larger, then the long-term irrational development and utilization caused by human, the water soil erosion of sloping farmland land in black soil area is becoming more and more serious. And the black soil has become thin and the decrease of land productivity and crop yield is also declining which has caused a serious threat to the sustainable use of agricultural water and soil resources and sustainable development of social economy in the black soil region. Therefore, utilization and protection of sloping farmland’s soil and water resources in the black area is imminent. Based on the background, the Hongxing Farm of Bei’an city in Heilongjiang province was selected as test which is located in the typical black soil region of Northeast C hina. In the area, soil amendments straw biochar was chosen as test materials which can not only improve soil fertility, soil structure and crop yield, but also can fix carbon mitigation and relieve climate change. Heilongjiang province is rich in resources of the grain production and straw, but the utilized rate of straw is low, so the application of modified straw biochar in black soil area reached a fully staffed effect. From the aspects of straw biochar to the physicochemical properties, soil structure, soil water movement, nutrient absorption and retention, study the influence of applying biochar in farmland black soil to the physicochemical properties, soil water movement and solute transport parameters of soil, establish the soil water movement and the solute migration model which is suitable for the study area, and then conduct the specific screenings rainfall simulation of soil water and solute distribution. The preliminary conclusions are as follows:（1） By adding biochar to the soil can lead to the increase of soil porosity in, the decrease of bulk density and the improvement of soil structure. The soil saturated water content, field capacity, wilting coefficient and soil water increased with increasing biochar content and application. And the increased range of different treatment of saturated water content was 16.50% 32.27%; field capacity was 0.32% 10.48%; the wilting coefficient was 0.28% 10.69%; the soil available water was 0.34% 10.36%. The degree of biochar addition effect on water parameters in turn was saturated water content, field water holding capacity, soil water content and wilting coefficient, and the influence of high rates of biochar treatment to soil moisture was higher than that of low.（2） The organic matter, ammonium nitrogen, available phosphorus, available potassium content and p H values increased with increasing biochar content, the content of organic matter and ammonium nitrogen had significant correlation with biochar content; while the available phosphorus, available potassium and p H value had no significant correlation with the amount of biochar.Comparing the ammonium nitrogen, available phosphorus, available potassium and organic matter spatial distribution in 100 t /hm2 treated soil and the control group, the former had better uniformity of content than the latter, and reduced the slope of the soil nutrients caused by differences. Soil ammonium nitrogen and available phosphorus both showed a significant positive correlation with organic matter, ammonium nitrogen and phosphorus also showed a significant positive correlation, while available potassium and organic matter almost showed negative correlation.（3） In the process of soil infiltration, the control experiment was the longest time and the rest in turn were 25 t /hm2,50 t / hm2 and 75 t / hm2 treatment, 100 t / hm2 treatment which was the shortest. Within the same time, add biochar cumulative infiltration was higher than that of the control treatment. The increased saturated hydraulic conductivity in the soil which was added biochar was 14.05%¹94.59% compared to the control soil. The more amount of biochar was added, the higher level of saturated hydraulic conductivity was increased more. And the influence of the different treatment of biochar to the soil water diffusivity was not the same,they were 25 t /hm2<50t /hm2<0t /hm2< 75 t /hm2<100t / hm2.（4） Biochar can promote the water holding capacity of soil, when the suction was in the range of 2¹100 range k Pa, the different value of moisture content under the lowest and highest suction were: 0t /hm2(0.196 g·g^-1)、25t /hm2(0.261 g·g^-1)、50t /hm2(0.259 g·g^-1)、75t /hm2(0.258 g·g^-1)and 100 t /hm2(0.298 g·g^-1); The positive correlation between the amount of basic content with biochar. The porosity and the soil water characteristic curve increased with the increase of the amount of biochar, and the higher amount of biochar increased more of the porosity and the soil water characteristic, the simulation value of soil water dynamic mass parameter increased with increasing the amount of biochar basically.（5） Through the simulate of soil moisture profile and solute distribution in the runoff under the two typical rainfall in the two months of July and August in 2015, it showed that the soil moisture increased gradually from the surface to the down, and with the increase of the amount of biochar, the vertical profile range of water content increased gradually. The change of surface soil moisture after 12 h of the rainfall was basically fluctuated in a certain range, but applying biochar influenced smaller to the soil moisture in the surface and the overall level of water content was high. The soil solute content in the surface was higher than the bottom and solute concentration increased with increasing amount of biochar.