Soil amendment with biochar: Consequences for plant and soil communities in a natural ecosystem

Background/Question/Methods

Climate change and depletion of fossil fuels urge mankind to adopt sustainable, so called bio-based energy sources. One of the most promising methods is oil production through thermally degrading organic wastes and biomass, in a process called pyrolysis. This process has charcoal or ‘biochar’ as a rest product. In soil, biochar is very recalcitrant and is therefore often proposed as way to sequester carbon. Biochar amendment is also advocated to promote crop growth in agricultural ecosystems. However, the ecological consequences of soil amendment with biochar on plant communities, soil biota, and their interactions are far less understood.

To test the effect of soil amendment with biochar under natural conditions, we set up a field experiment in a Dutch nature reserve in April 2011. The experiment consists of four treatments: two biochar treatments (Biochar produced at 400^oC and at 600^oC), a treatment in which we incorporated the non-pyrolised biomass (Hay), and a control treatment (no substrate added). After incorporating the substrates, all plots were sown with a mixture of 18 grassland species that are common to the area. In August 2011 we measured plant community characteristics, individual plant performance, soil nutrient characteristics, and soil biotic characteristics (e.g. bacteria, fungi, nematodes, enchytraeids).

Results/Conclusions

Already after one growing season we observed strong effects of biochar amendment as  plant community composition was significantly altered by biochar addition. Abundance of legumes was enhanced  in plots with biochar, whereas grasses were more common in the control plots. Not only legume cover was higher in biochar plots, but also individual legume plants were significantly larger in plots amended with biochar. We will report on further experiments elucidating the underlying mechanisms for this increased legume performance. Also soil nutrient characteristics were changed by biochar amendment. Biochar addition increased the availability of some macro-nutrients, but also increased the soil pH. Remarkably, only few effects on the soil biotic community were found. However, the effects on soil nutrients and vegetation composition can cascade into higher level trophic layers over time. We will discuss how a bio-based economy can change plant and soil communities, and what the consequences are for natural ecosystems in a changing world.