Effect of biochar on soil physical properties in two contrasting soils: An Alfisol and an Andisol

Improving soil physical properties by means of biochar application has been proposed in recent publications. The objective of this study was to investigate to what extent the addition of corn stover (CS) and biochars produced from the pyrolysis of corn stover feedstock (CS) at 350 and 550°C temperatures (CS-350, CS-550) affected aggregate stability, volumetric water content (θV), bulk density, saturated hydraulic conductivity (Ks) and soil water repellency of specific soils. Organic amendments (CS, CS-350, CS-550) were incorporated into a Typic Fragiaqualf (TK) and a Typic Hapludand (EG) soils at the rate of 7.18tCha−1, which corresponded to 17.3, 11.3 and 10.0tbiocharha−1 for the CS, CS-350 and CS-550 treatments, respectively. After 295d of incubation (T295), soils were sampled as (i) undisturbed samples for bulk density and Ks; and (ii) mildly disturbed samples for θV (at −15, −1, −0.3, −0.1, −0.08, −0.06, −0.04, and −0.02bar), aggregate stability and soil water repellency. The θV at time 0 (T0) was also determined at −15, −1 and −0.3 matric potentials for the different treatments. Biochar application significantly increased (P<0.05) aggregate stability of both soils, the effect of CS-550 biochar being more prominent in the TK soil than that in the EG soil, and the reverse pattern being observed for the CS-350 biochar. Biochar application increased the θV at each matric potential although the effect was not always significant (P<0.05) and was generally more evident in the TK soil than that in the EG soil, at both T0 and T295. Biochar addition significantly (P<0.05) increased the macroporosity (e.g., increase in θV at −0.08 to 0bar) in the TK soil and also the mesoporosity in the EG soil (e.g., increase in θV from −1 to −0.1bar). Both biochars significantly increased (P<0.05) the Ks of the TK soil, but only CS-350 biochar significantly increased (P<0.05) the Ks in the EG soil. Biochar was not found to increase the water repellency of these soils. Overall results suggest that these biochars may facilitate drainage in the poorly drained TK soil. However, the present results are biochar-, dose- and soil-specific. More research is needed to determine changes produced in other biochar, dose and soil combination, especially under field conditions.