Effects of biochar on soil properties and erosion potential in a highly weathered soil

Highly weathered soils in humid Asia are characterized by low soil fertility and high soil erosion potential. This study evaluates the influences of biochar made from the waste wood of white lead trees (Leucaena leucocephala (Lam.) de Wit) on the physicochemical and biological properties of long-term cultivated, acidic Ultisol. This study used three application rates (0%, 2.5%, and 5% (wt/wt)) of the biochar with an incubation time of 105d for all cases. Soils were collected at 21d, 42d, 63d, 84d and 105d during the incubation period to evaluate changes in soil properties over time. A simulated rainfall event (80mmh−1) was performed to estimate soil loss for all treatments at the end of the incubation time. Experimental results indicate that applying biochar improved the physicochemical and biological properties of the highly weathered soils, including significant increases in soil pH from 3.9 to 5.1, cation exchange capacity from 7.41 to 10.8cmol (+) kg−1, base cation percentage from 6.40 to 26.0%, and microbial biomass carbon (MBC) from 835 to 1262mgkg−1. Compared with the control (i.e., no biochar), biochar application decreased bulk density from 1.4 to 1.1Mgm−3, increased Ksat by 1.8 times and increased the mean weight diameter (MWD) of soil aggregates from 2.6cm to 4.0cm. Incorporating biochar into the soil significantly reduced soil loss by 50% and 64% at 2.5% and 5% application rates, respectively, compared with the control. The formation of macroaggregates in the biochar-amended soils is the critical factor to improve soil erosion potential. Based on these results, a 5% application rate of biochar is considered as suitable for highly weathered soil because this application rate efficiently improves soil physiochemical properties and reduces soil loss. Soil physicochemical properties have been clearly improved and soil erosion potential has been obviously reduced by biochar application in the highly weathered soil. This study interprets alteration of soil aggregate size in terms of soil micromorphology and well explains improved mechanism of soil erosion after biochar application (Fig. 4). Fig. 4 also demonstrated that the biochar could help to bind microaggregates by microbial activity. The redistribution of the proportions of macro- and microaggregates (aggregate sizes obviously increase with biochar application rates) might be the critical factor to reduce soil erosion potential. Fig. 4. Micrographs of thin sections of soils without and with amen