Adding biochar to the composting process: effect of the resulting amendment in agricultural soils

Abstract

Agricultural soils are reaching critical points in soil health and functionality. The main soil issues are loss of structure, low fertility and soil carbon deficits. Previous experiences support that mixing compost and biochar and using the mixture as soil amendment can improve plant growth by increasing water and nutrient retention and decreasing soil compaction and, in addition, being a sustainable option were residues are reused and C sequestrated in soils. Moreover, some recent studies go further and suggest the application of biochar in composting process. In our study, a review of the effect of applying co-composted biochar in agricultural soils was done. Nineteen worldwide articles studying soil and plant parameters as soil organic carbon, soil water content, pH, cation exchange capacity, greenhouse gases emission, plant nutrient uptake and plant yield, were reviewed. Co-composted biochar (COMBI) application in soils generally resulted in beneficial changes for soil health as an increase of soil organic content, soil water content, cation exchange capacity (especially when applied in high doses), crop yield and a reduction in N2O emissions. Moreover, co-composted biochar as amendment also regulates soil pH in the correct range between 5.5 and 7.5. Regarding CO2 emissions, different trends were observed among reviewed studies and more investigation needs to be done to study soil CO2 emissions together with other emissions produced in the whole life of co-composted biochar and compared with those emissions that biomass would have emit if was not converted into this material. All these trends greatly vary with different experimental conditions as soil type, soil pH and COMBI application rates. Finally, further work on the application of co-composted biochar in soil quality and plant growth is still necessary to understand the effect of co-composted biochar when applied in different conditions as soil type, soil pH, location, amendment application rate, among others.