Biochar Derived from Anaerobic Digestion Effluents to Improve Aggregate Stability in Mexican Clayey Soils.

Biochar application to soil can improve soil properties such as fertility, water holding capacity, and aggregation. The importance of soil aggregates in agricultural practices is pronounced particularly in semiarid and poorly structured soils such as those found in central Mexico. The objective of this study was to understand the effects of biochars derived from solid part of anaerobic digestion effluent (ADE) on soil aggregation and stability. Soils were collected from 20 cm in uncultivated fields in Silao (Pellic Vertisol) and Pénjamo (Haplic Phaeozem), Guanajuato State. The ADE was collected from anaerobic digesters in a slaughterhouse in Leon, and its solid part was pyrolysed at 550°C for 2 hr under limited oxygen. An incubation experiment was conducted for 2 soil types and 2 ADE biochar (ADE-B) application rates (0% and 1%, w/w) at 30°C for 70 d. Emission of CO₂ from Vertisol and Phaeozem soils with ADE-B was rapid during the first 7 and 21 d, respectively, then stabilized around 42 and 72 d, respectively. Phaeozem soils released 1.8 times more cumulative CO₂ than Vertisol by the end of incubation. Mean weight diameter of soil aggregates was significantly greater on 7 d in Vertisol and 14 d in Phaeozem soils with ADE-B compared to those without, respectively. In Vertisol with ADE-B, total carbon (TC) concentrations found within macro aggregate significantly increased on 7 d from 0 d, then significantly decreased on 70 d, while TC within nano aggregate significantly increased on 70 d from 7 d. Similar trends were observed in Phaeozem with ADE-B. It appeared that microbial boost induced by ADE-B caused soil aggregation on 7 d particularly in macro aggregate, however may have disaggregated into nano aggregate by 70 d. With ADE-B, soil aggregates formed in Phaeozem possibly exhibited greater stability than Vertisol due to higher soil organic matter.