Measuring the Impact of Melaleuca Quinquenervia Biochar Application On Plant Growth, Microbial Gas Flux, and Soil Quality.

Globally, modern agricultural practices contribute to greater than 20% of global greenhouse gas (GHG) emissions. In recent years, biochar (BC) has been a topic of growing interest as it is claimed to be a mechanism for carbon sequestration and an ideal amendment for improving soil quality.   In South Florida, Melaleuca quinquenervia has become a paramount environmental problem and has been characterized as one of the most aggressive and wide-spread invasive species. The purpose of this research is to convert M. quinquenervia biomass into BC and measure how its application at two rates impacts plant growth, microbial gas flux, and soil quality in a greenhouse experiment using Phaseolus vulgaris L.  Local soil was amended with pulverized M. quinquenervia biochar at 2% and 5% by weight for a total of eight replicates, control soil had no biochar.  Phaseolus vulgaris seeds were started in a 1:1 soil: compost mixture and transplanted at first leaf stage to trial pots. Throughout the growing period plant growth was measured using chlorophyll, root and shoot ratio, root architecture, height, and specific leaf area. CO₂ flux from the soil was measured biweekly using 72 hour soil incubations analyzed with gas chromatography. Soil quality was measured using total and available nutrient content, cation exchange capacity, and water holding capacity. Overall, plant production was greatest in the control group. Olsen extraction results proved the presence of M. quinquenervia BC in soil reduced available P significantly.   Other nutrients, such as Cu and Fe, were also made less available for plant growth.  There was a difference in initial CO₂ emissions from the treatments and control group, however only the 5% application reduction was significant (p <.009).  South Florida soils are highly calcareous with high pH values.  Further research should be conducted to better assess the interaction of BC amendments in these soils.