Biochar

Biochar soil amendment - influence on bacterial S and P mobilization

Biochar has exhibited many potential agricultural benefits, such as plant growth promotion effects, increased soil water retention and neutralisation of acidic soil pH. Its impact on microbial-mediated macronutrient bio-availability, however, is largely unknown. This is particularly the case with sulfur (S) and phosphorous (P). Plants rely on microorganisms to mineralize organic and inorganically bonded S and P for their own requirements.

Replicate pot experiments of ryegrass Lolium perenne var. Malambo, spring barley Hordeum vulgare var. Sy taberna and tomato Lycopersicon esculentum were established. Pot soils were treated with 1 or 2% biochar (w/w, made from Miscanthus giganteus, pyrolysed at 600oC) or were kept biochar-free as a control. Biochar amendments resulted into a significant growth promotion effect with all plants tested. All combinations of plant and biochar treatments showed a “liming effect” in the pot soils in the form of raised pH and trends towards increased soil water retention were identified in connection with the addition of biochar. From rhizospheric soil extracted from each plant replicate, Most Probable Number analysis was conducted and Colony Forming Units were established using minimal media to grow bacteria capable of mobilising a) S from aromatic sulfonates, b) P from phosphate-esters, c) P from phosphonates, and d) P from tricalcium-phosphates. Greater abundance of S and P mobilising bacteria were associated with both biochar treatments against the control treatment for each plant.

Very little is known about the potential role of bacteria colonizing the char. These results suggest that increased numbers of S and P mobilising bacterial colonizers in biochar amended soil could be beneficial for plant growth through enhanced nutrient mobilisation.

Part of this study is now published: Fox, A., Kwapinski, W., Griffiths, B.S., and Schmalenberger, A. (2014). The role of sulfur- and phosphorus-mobilizing bacteria in biochar-induced growth promotion of Lolium perenne. FEMS Microbiology Ecology 90, 78–91

Biochar soil amendment in pot experiments