生物炭对黄绵土水分入渗和持水性能的影响

Effects of biochar on water infi ltration and water holding capacity of loessial soil

基于室内一维土柱入渗试验,定容重条件下研究了生物炭粒径(1—2 mm和≤0.25 mm)和添加量(10 g?kg^(-1)、50 g?kg^(-1)、100 g?kg^9-1)和150 g?kg^-1))对扰动黄绵土的水分入渗过程及持水能力的影响。结果表明:生物炭明显降低了黄绵土的入渗能力,黄绵土的湿润锋深度与累积入渗量随着生物炭添加量的增加而降低,且小粒径生物炭对黄绵土入渗能力的降低作用强于大粒径;生物炭明显增加了黄绵土的持水能力,且随添加量增大而增大,小粒径生物炭的促进作用优于大粒径;添加生物炭后黄绵土湿润锋深度与时间关系可用幂函数描述;Kostiakov、Philip、Horton入渗模型均能较好模拟生物炭添加后黄绵土累积入渗量随时间变化,其中,Kostiakov模型拟合精度更高;van Genuchten公式可以用来描述添加生物炭后黄绵土持水特征。该研究结果为添加生物炭后的黄绵土适宜性评价提供了土壤水分方面的参考依据。

Background, aim, and scope Biochar is a newly constructed scientific term which is defined as ＂a carbon（C）-rich and non-pollution product when biomass such as wood, manure or leaves is heated in a closed container with little or unavailable air＂. It has the properties of high internal surface area, microporosity, non-biological and biological stability. It has been widely proposed as a promising novel alternative of soil amendment to improve soil physical and chemical properties, to reduce the biological effectiveness of soil pollutant, as well as to reduce the emission of carbon dioxide and other greenhouse gases. However, to date, the effects of biochar addition on soil hydraulic properties, and the influencing mechanism of biochar addition on water retention and holding capacity are still unclear. Materials and methods Effects of biochar with two sizes （1 --2 mm and ≤0.25 mm） and 4 doses （10 g·kg^-1, 50 g·kg^-1, 100 g·kg^-1 and 150 g·kg^-1） on wetting front, cumulative infiltration and retention curves of loessial soil were explored through simulated experiments in laboratory. The loessial soil was collected from the soil surface （0--20 cm） of a field without tillage in Ansai Ecological Experimental Station, Shaanxi Province in northwest China. Experiment with biochar was charcoal-derived biochar and its carbon mass fraction was 85%. Results The results showed that （1） the infiltration capacity was obviously decreased and water holding capacity was significantly increased compared to the control due to the biochar addition in loessial soil. When the particle size was the same and within a certain infiltration time period, in addition to the ≤0.25 mm treatment and the cumulative infiltration curve almost superposition under the 10 g·kg^-1, 50 g·kg^-1 and 100 g·kg^-1 treatments, cumulative infiltration and wetting front moving rate tended to decrease with the increasing content of biochar, while water holding capacity tended to increase with the increasing content of biochar. Under the conditions of the same biochar addition dose, cumulative infiltration and wetting front moving rate tended to decrease with the particle size decreased within a certain infiltration period （40 minutes after infiltration start）, while water holding capacity increased with the particle size decreased, but there was no significant effect on water holding capacity at the dose of 10 g.kg-~. 40 minutes after infiltration start, the wetting front moving rates for 1--2 mm treatment with 10 g·kg^-1, 50 g·kg^-1, 100 g-kg-~ and 150 g·kg^-1 doses were decreased by 5.72%, 12.47%, 10.23% and 17.49%, respectively, compared with the control, cumulative infiltration were decreased by 11.17%, 24.48%, 22.07% and 31.10%, respectively; the wetting front moving rates of ≤0.25 mm treatment with the addition doses of 10 g·kg^-1, 50 g·kg^-1, 100 g·kg^-1 and 150 g·kg^-1 were decreased by 13.49%, 14.79%, 22.79% and 36.28%, respectively, compared with the control, and cumulative infiltration were decreased most by 57.93% with the dose of 150 g·kg^-1. The averaged wetting front moving rate and cumulative infiltration were decreased by 16.69% and 27.79% in loessial soil with the comparison to the control. Overall, biochar addition reduced the water infiltration capacity and increased the water holding capacity for loessial soil. （2） Variation of the wetting front with time demonstrated a power function relationship, the determination coefficient was 0.997--0.999. Kostiakov, Philip and Horton infiltration model were successively used to simulation the soil water infiltration process and Kostiakov infiltration model of which determination coefficient was 0.989--0.998 fitted best. （3） van Genuchten model was suitable for simulation the soil water holding process with biochar application, and the determination coefficient of it was 0.995--0.999. Discussion The results showed that the infiltration capacity was decreased and water holding capacity was increased with the biochar amendments to loessial soil. Biochar has high internal porosity and surface area and it creates a soil conditioning agent that can lower bulk density, increase the content of soil clay, affect pore size distribution and increase soil porosity. Therefore, it inhibited the infiltration capacity and improved water holding capacity of loessial soil. Conclusions The results showed that the loessial soil infiltration capacity tended to decrease with the increasing content of biochar, decreased with the particle size increased, while water holding capacity tended to increase with the increasing content of biochar, and the water holding capacity was best with the smallest particle size （~〈0.25 mm） biochar addition in loessial soil. The results also showed that variation of the wetting front with time demonstrated a power function relationship, the determination coefficient was 0.997--0.999. Kostiakov, Philip, Horton infiltration model were successively used to simulation the soil water infiltration process and Kostiakov infiltration model fitted best. van Genuehten model was suitable for simulation the soil water holding process with biochar application. Recommendations and perspectives The data suggested that the use of biochar as soil amendment in loessialsoil plays an important role in increasing soil water holding capacity, and providing a scientific basis for the evaluation on the influence of biochar application on soil hydrology in the Loess Plateau.