Production of aqueous biochar biocatalyst for agricultural sustainability

Abstract

Addition of biochar during composting will reduce the loss of nitrogen and produce nutrient stabilized organic fertilizer. Better results can be obtained by using biologically activated/catalyzed biochar. Therefore, a study was conducted to produce and add activated biochar during the active phase of composting process. To produce an aqueous biocatalyst, slurry was prepared by mixing shredded Gliricidia sepium leaves(1 kg), water (3 L) and Eppalawa rock phosphate (8 g). The biocatalyst was prepared under aerobic conditions in an aerobic reactor which was fabricated using a 25 L plastic container, Perspex pipes, and an aerator. 1.5 kg of biochar produced from Gliricidia sepium wood in a pyrolyzer was added to the slurry intermittently until it reaches neutral pH. It took 24 days to reach a neutral pH value. The highest available nitrogen of 243 mg/L, total potassium of 8,125 mg/L and total phosphorus of 53.4 mg/L was obtained on 15ᵗʰ day at the pH 6. Through a repeated experiment, it was found that biocatalyst can be produced within 5 days. Two compost piles were prepared using fresh immature Panicum maximum grass (18 kg) and Gliricidia sepium leaves (2 kg)/ pile. Cultured biochar biocatalyst was mixed with 6% dry weight basis to one pile and raw biochar (6%) was incorporated to the other pile. N, P, K levels of all compost piles after 8 weeks were within the recommended levels. The highest nitrogen of 20.3 g/kg, and potassium of 83.71 g/kg remained in 6% biocatalyst compost. Phosphorus content of 6% biocatalyst compost was 0.67 g/kg of dry compost and it was 0.72 g/kg in 6% biochar compost. The pH value of produced compost with biochar biocatalyst was 8.8 and it was 9.2 in compost with 6% biochar. The made compost is very suitable and perhaps cost-effective for acidic soils to improve soil nutrient status unlike the addition of lime.