Biochar from water hyacinth (Eichornia crassipes) and its impact on soil biological activity

Biochar is a useful material for carbon storage in soils. In this report, we explored conversion of water hyacinth (Eichornia crassipes) to biochar as a sustainable weed management strategy, as it also has potential for improving soil quality. Eichornia biomass samples were carbonised with limited supply of air in a muffle furnace at varied temperature (200 to 500°C) and residence time (30 to 120min). The biochar yield decreased with temperature and time, but biochar carbon stability increased with temperature. The optimum condition for obtaining maximum stable carbon in Eichornia biochar (EBC) is 300–350°C temperature with 30–40min residence time. TGA and FTIR studies showed that EBC has increased aromaticity and carbon stability compared to the starting biomass. Impact of the EBC on soil quality was studied using a red soil, from Dhanbad, India. Soil biochemical properties (dehydrogenase, fluorescein hydrolases, catalase, respiration, active microbial biomass) and maize seedling growth were used to investigate the effects of biochar addition to the soil. Maize seedling vigour index increased from 1.0 at control to 1.61 in 20g/kg EBC treatment. The maximum increase in soil enzymes like acid phosphatase activity (+32%), alkaline phosphatase activity (+22.8%), and fluorescein hydrolases activity (50%) occurred at the EBC dose of 20g/kg. EBC significantly enhanced the soil biological activity particularly the active microbial biomass which has increased by 3 times and soil respiration by 1.9 times. The study shows that the waste Eichornia weed could be gainfully utilised as a soil quality amendment material by converting it to EBC. •Conversion of Eichornia to biochar is a sustainable weed management strategy.•Pyrolysis at 300°C for 30min yielded the desired biochar from Eichornia.•H/C, O/C ratios, TGA, and FTIR indicated the aromaticity and stability of biochar.•Zea mays seedling vigour index increased (61%) due to biochar addition.•Soil enzymes and microbial activity increased due to biochar incorporation.