Combined biochar and manure addition to an agricultural soil benefits fertility, microbial activity, and mitigates manure‐induced CO₂ emissions

Abstract

The importance of blending biochar into manure prior to its application as a soil amendment was investigated by this laboratory and field study, hypothesizing an (i) increase in soil fertility; (ii) improvement in microbial activity; and (iii) reduction in manure‐induced CO₂ emissions after combining amendments. Biochar was mixed with manure (50:50 V/V) and aged in field conditions for 6 months whereafter pristine biochar, manure, and manured biochar (50:50 V/V) were incorporated into an agricultural drought‐prone Regosol. All treatments and soil mixtures were incubated, with laboratory measurements of CO₂ emissions taken using a coupled column respirometer set up, whilst nutrient availabilities as well as enzymatic activities were also tested.

Demonstrable benefits of the biochar when blended to manure were exemplified in reduced CO₂ emissions, by 60 % compared to manure alone, and improved C and N acquisition by microorganisms. When applied to soil, blended biochar‐manure did not enhance CO₂ emissions, but did significantly improve soil fertility by the avoidance of leaching of non‐plant consumed nutrients from the soil (e.g., NO₃^‐ by 58 %). A significant increase in functional diversity indices in the presence of manured biochar highlights the added value of the blended approach. Field application yielded reduced effects;, manure induced a higher carbon and nitrogen mineralization (thus potentially higher C and N emissions via CO₂, CH₄ and N₂O) as well as a higher microbial functional diversity. Further studies should verify the effects observed here in a range of soil types and climates.