施用生物炭对紫色土坡耕地耕层土壤水力学性质的影响

Effects of biochar application on tilth soil hydraulic properties of slope cropland of purple soil

该研究通过野外坡耕地小区施用1%秸秆生物炭1年后的对比试验,揭示生物炭对川中丘陵区紫色土耕作层土壤水力学参数、大孔隙度及其对饱和导水率的贡献率所产生的影响。试验设对照区与施用生物炭区2个处理,各处理有3个平行小区,耕作层土壤分为表层和亚表层（2-7和〉7-12 cm）。比较2个处理小区试验结果,可以发现：1）施用生物炭导致植物难以利用的土壤滞留水和易流失的结构性孔隙水的含量（θstr）下降,而基质性孔隙中植物有效水含量显著提高（P〈0.05）,由（0.058±0.003）cm3/cm3增加至（0.085±0.002）cm3/cm3;2）表层和亚表层土壤中对产流起主要贡献的半径〉125μm的总有效孔隙度分别平均增加54%和8%,其中孔径〉500μm的孔隙增加最为明显,高达110%和355%;3）表层和亚表层土壤的饱和导水率分别平均增加45%和35%。研究证明,施用生物炭,一方面,能增加土壤有效水的持水量,有利于植物抗旱;另一方面,提高土壤导水率,有利于水分入渗,从而减少地表径流及土壤侵蚀的发生。

Biochar is a kind of solid residual produced by thermal decomposition of orgnic material under limited or absent supply of oxygen, and relatively low temperatures, biochar has the properties of high internal surface area and microporosity, furthmore, non-biological and biological stability. It used as a soil amendment could greatly improve soil physical and chemical properties, reduce the biological effectiveness of soil pollutant and greatly reduce the emission of carbon dioxide and other greenhouse gases and sequestrated soil carbon in recent years. In this study, a one-year field trail of biochar application in the hilly area of central Sichuan Basin, was carried out in sloping farmland plots, which was located at Yanting Agro-ecological Experimental Station of Purple Soil（105°27′E,31°16′N）, Sichuan, Southwest China, to investigate the effects on hydraulic properties of cultivated purple soil（an entisol）. Two treatments were set up： control（NPK） and biochar amended（NPK-BC）, with each being replicated three times. Comparison between biochar amended and control plots was made by determining soil hydraulic parameters, soil pore size distribution and the contribution of each pore size to flow at two depths（2-7 and 7-12 cm） of the plough layer. Results showed that： 1） due to biochar application, the soil contact angle was increased by 6.7°and 0.5°at the 2-7 and 7-12 cm depth, respectively. This implies that soil water absorption ability was increased and nutrients will be more easily dissolved in the soil.2） After one year of biochar application, the residual water content（θr）,which is unavailable to plants and water content in structure pores（θstr）, which is easy to be drained out,was decreased, respectively. But the water content in soil matrix pores（θtxt）, which is available to plants, increased significantly（P〈0.05） from 0.058±0.003 cm3.cm-3 to 0.085±0.002 cm3/cm3. This implies its stronger ability to retain plant-available water after biochar amended,; 3） due to biochar application, The effective porosity of r125 μm pores increased by 54% and 8% at the 2-7 and 7-12 cm depth, respectively.Particularly, the effective porosity of r500 μm pores increased most markedly, reaching 110% and 355% for the two depths, respectively. This shows that biochar application reduces the 250 r 500 μm pores volume in the soil, but increased the volume of smaller pore（125 r 250 μm） and larger pore（r500 μm）; 4） the saturated hydraulic conductivity at the two depths（2-7 and 7-12 cm） increased by 45% and 35%, respectively, after a year of biochar application. Tension infiltration data show that soil macropores（r125 μm） were the main contributing（accounting for 92-94%） pores to the fast drainage at the 2-7 and 7-12 cm depth, under control and biochar amended r, in spite of their very low percentage（3-4%） of total porosity. 5）Therefore, it can be inferred that, on one hand, the application of biochar could increase the soil＇s capacity to hold plant-available water and thus enhance resistance to drought; on the other hand, it can also enhance water permeability of soil, which can reduce surface runoff and potential soil erosion.