Does carbon negative biochar tighten the nitrogen cycle?

An ancient Amazonian soil practice of applying charcoal to soil to produce Terra preta, could provide us with one of the solutions to global climate change, whilst tightening leaky nitrogen cycles. The modern equivalent process, biochar production, produces carbon negative bio-fuel and biochar, which when added to soil has been shown to improve soil properties and even reduce greenhouse gas emissions. Evidence from Terra preta soils and recent studies have revealed that biochar carbon is extremely stable; locking carbon away for millennia, making biochar addition to soil, a viable long term means of sequestering carbon that could have significant impact on climate change. Preliminary studies have shown that biochar soil amendment can increase crop yields; however, more detailed analysis of the inherent mechanisms of how biochar affects nutrient cycles in soils is required. The project will focus on understanding how biochar addition alters the nitrogen cycle and the mechanisms controlling greenhouse gas emissions.

Ancient Amazonian soil practices of nurturing Terra Preta through the addition of charcoal to soil and its modern equivalent, biochar production followed by soil incorporation, could provide humanity carbon farming solutions to global climate change and escalating food demand. Global studies and our evidence suggests that biochar amendment causes fundamental changes in soil nutrient cycles, resulting in marked increases in crop production, particularly in infertile tropical soils with low soil organic matter contents.In this project we offered insights into the mechanisms underpinning these observations by focusing attention on the soil nitrogen (N) cycle, specifically on hitherto unmeasured processes of organic N cycling in both tropical and temperate arable soils.In both temperate (Austrian) and tropical (Kenyan) soils we found that biochar addition increased the rates of nitrification, a biogeochemical process which is crucial in determining the efficiency of plant nitrogen up take and consequent plant growth. We also showed that biochar addition led to a dramatic deceleration of organic nitrogen cycling in soils which could be explained by the protection of organic matter from degrading soil enzymes. The high surface areas and macro-pores structure of biochar is likely provides the soil microbial biomass with favourable microhabitats, protecting them against grazers or competitors and allowing for the co-location of nutrients and increased soil water retention. Increased plant water use efficiency, more crop per drop, in biochar amended soils was observed in both our temperate and tropical studies, providing us with promising technological leads to mitigate future drought scenarios. In tropical soils biochar addition also had associated liming effects with pH values greater +1 pH which might have explained the increases in nitrification rates observed. In all the field and greenhouse studies conducted within this project, we showed that biochar addition to soil had minimal impact on nutrient immobilization, the main problem associated with adding un-charred carbon, such as straw, to soil. Indeed in all our experiments we showed that biochar addition to soil had insignificant or very positive impacts on crop yields particularly when applied in combination with small quantities of inorganic fertilizer. We are therefore confident that agronomic practice of biochar addition to soil could play a realistic and significant role in mitigating global climate change.