Optimization of biochar additions for enriching nitrogen in active phase low-temperature composting

This paper examines the effectiveness of combining biochar and compost to test if organic fertilizers can be enhanced by the addition of biochar in the active phase of composting high-nitrogen source materials. Therefore, a small-scale experiment was conducted for 40 days to investigate the effects of nitrogen conservation. Four composting piles including a control without biochar were prepared with 18 kg of shredded immature Panicum maximum grass and 2 kg of Gliricidia sepium leaves. Biochar additions were 3%, 6%, and 9% calculated on dry weight basis. There was no significant difference between treatments for temperature (~ 29.5 °C) and pH (~ 9). A novel material balance approach based on total fixed solids provided the means to determine the actual volatile solid contents, i.e., nitrogen levels during the decomposition process. According to this, the actual nitrogen content of 6% biochar mixed pile (16.203 mg/g) was significantly different to the others by having a higher mean value. Similarly, the mean nitrogen loss was lower (− 5.66%) than measured in the other treatments. Nitrogen loss is low in the biochar mixed piles because of nitrogen adsorption compared with 24% loss in control. The kinetic study on nitrogen postulates entrapping ammonia production and increasing enzyme urease activities. First-order rate kinetics could be used to predict the reduction of C/N ratio of 30 to 9 in 65 days. Hence, 6% biochar treatment was discovered to be the optimum to prevent excessive oxidation or volatilization of ammonia during the active phase low-temperature composting and fix atmospheric nitrogen.