Effect Of Biochar Application On Soil Erosion Of Loess Slopes

Biochar is a material that basic utilization of agriculture and forestry waste. It has a bright prospect due to its good structure and physicochemical properties. Under the background of climate change, shortage of energy, environment pollution, food crisis and the limitation of agricultural sustainable development, biochar has already been a hotspot in the fields of agriculture, energy and environment. In the field of agriculture, research in the improvement of soil structure and physicochemical, Increase crop production quality, which biochar as a soil amendment, has been widely undertaken. Loess Plateau is the most serious soil erosion region in the world. The local agricultural production and ecological restoration has been limited in some extent by poor soil fertility, water shortages, and serious erosion. Biochar itself contains nutrients and also has the potential application value in improving soil structure and soil-water status. In the view of above reasons, we applied biochar in soil to explore the effect of soil erosion.In this study, we applied methods which include indoor artificial rainfall simulation and soil samples’ physical and chemical properties analysis. Five content(0%, 1%,3%,5% and 7%) and five size of biochar(2-1mm, 1-0.25 mm, <0.25 mm, <1mm and <2mm) are designed to thorough mix with Loessal soil. Saturated soil hydraulic conductivity, soil aggregate, soil and sediment volume fractal dimensions, nutrient content of sediment and biochar content in sediment are indicators to evaluate the consequence of biochar. While we compared soil erosion consequences in 2014 and 2015 with the method of indoor artificial rainfall simulation. The main research findings are shown as follows:(1) Application of biochar in soil has a significate effect to saturated soil hydraulic conductivity in the same soil bulk density. Dates, through assaying soil saturated hydraulic conductivity with constant water head, showed that saturated soil hydraulic conductivity is becoming enlargement in the wake of biochar content and biochar size decreasing. Saturated soil hydraulic conductivity can also be enlarged after incubation in nature condition.(2) After 7 months’ incubation in nature, we applied drying sieving and wetting sieving methods to analysis the stability of soil aggregate. Biochar application made the ‘>2mm group’ and ‘>0.25 mm group’ of soil aggregate, mean weight diameter(MWD), and geometric mean diameter(GMD) increased, soil percentage of particle breakage(PAD) is also increased. This indicate the size of soil aggregate is become larger, but the new formation soil aggregate is not stable. The causes of this phenomenon is the incubation time is too short. Biochar is an inert material, short incubation can gain little result. So we advance the long incubation time experiment to monitor soil aggregate forming, to explicit the biochar in soil aggregate formation process and consequence.(3) Soil volume fractal dimension is increasing with the increasing of biochar content and decreasing of biochar size. A variation trend of sediment volume fractal dimension is that the sediment volume fractal dimension enlarged at first and then stable statue in rainfall duration. Soil volume fractal dimension has a significant related ship with amount of soil erosion, a quadratic function. no obvious relate with runoff amount.(4) The change of soil nutrient in mixed soil. Nitrogen and phosphorus in mixed soil are enlarged with the increasing of biochar content, but potassium is decreased. During the process of rainfall, total nitrogen of the sediment sample is decreased, total phosphorous is enlarged, and total potassium has no regular. After the rainfall, the mean of total nitrogen and total potassium are larger than blank test of sand grain. Reversed consequence of the mean of total phosphorus. Those outcomes told us that biochar releases nitrogen and potassium in the process of rainfall, and phosphorus might be lost in runoff, also might been adsorbed with biochar.(5) Effect of biochar application on soil erosion is significant. Biochar content was responsible for 40.64% and 33.61%, respectively, of the variation of soil erosion amount and runoff yield. Along with the increasing of biochar content, amount of soil erosion and runoff have an enlarged tendency. Biochar size was responsible for 5.03% and 5.27%, respectively, of the variation of soil erosion amount and runoff yield. With the decrease of biochar size, soil erosion amount can be enlarged and runoff amount can be decreased. Amount of soil erosion and runoff were decreased after 7 months’ incubation in nature. That might be the reasons like that large soil aggregate formed after incubation, which could make soil saturated hydraulic conductivity enlarged, amount of runoff decreased, and scouring force of runoff might be decreased. But the incubation time is so short, the stability of soil aggregate is poor, which made soil easy crushed during each rainfall event. So soil erosion amount has a decreased trend, hasn’t reached a significant level. This leave us a task to research that enlarge the incubation time can make a good field.(6) The concentration of biochar in sediment is decreased in a power exponent during the process of each rainfall event. In the begin 10 min of rainfall, biochar concentration in sediment is decreased sharply, then it enters into a stationary phase. In soil, biochar can be enriched for biochar content surpass 3%, and the enriched phenomenon is receded, when biochar size decreased. In reason of erodibility of biochar, the loss amount of biochar is increased with biochar application enlarged and the size of biochar decreased.For analysis above indexes, we found that biochar could change soil erosion status in reason to change soil physicochemical properties. We have to establish a long-term monitoring system to explicit the consequence and mechanism in effect of biochar application in soil erosion.