Zhencai Sun, Agroecology, Aarhus University, Viborg, Denmark, Per Moldrup, Department of Biotechnology, Chemistry and Environmental Engineering, Aalborg University, Aalborg, Denmark, Anders L. Vendelboe, Deptartment of Agroecology, Faculty of Science and Technology, Aarhus University, Viborg, Denmark, Esben Wilson Bruun, Department of Chemical and Biochemical Engineering, Technical University of Denmark, Lyngby, Denmark, Lars Elsgaard, Department of Agroecology, Faculy of Science and Technology, Aarhus University, Viborg, Denmark and Lis de Jonge, Department of Agroecology, Aarhus University, Tjele, DK-8830, Denmark
Biochar addition to agricultural soil has been reported to reduce climate gas emission, as well as improve soil fertility and crop productivity. Little, however, is known about biochar effects on soil structural characteristics. This study investigates if biochar-application changes soil structural characteristics, as indicated from water retention and gas transport measurements on intact soil samples. Soil was sampled from a field experiment on a sandy loam with four control plots (C) without biochar and four plots (B) with incorporated biochar at a rate of 20 tons per hectare (plot size, 6 x 8 m). The C and B plots were placed in a mixed sequence (C-B-C-B-C-B-C-B) and at the same time the eight plots formed a natural pH gradient ranging from pH 7.7 to 6.3. We determined bulk density, saturated hydraulic conductivity (K-sat), soil water retention characteristics, soil-air permeability, and soil-gas diffusivity on intact 100cm3 soil samples (5 replicates in each plot). We found that biochar application significantly decreased soil bulk density, hereby creating higher porosity. At the same soil-water matric potential, all the soil-gas phase parameters (air-filled porosity, air permeability and gas diffusivity) increased significantly after biochar incorporation .This suggests that biochar application enlarged the proportion of larger soil pores. In agreement with this, also K-sat values were higher in the B plots. The water holding capacity of the soil also increased with biochar incorporation, likely due to the high micro porosity of added biochar. In conclusion, the results showed that biochar addition to soil changed key soil structural parameters at least in the short term (1 year). In perspective, the long-term variations in soil structural parameters and related changed in microbial activity indexes following biochar addition will be investigated in the same field plots.