Response of biochar amendment for substituting organic fertilizer ingredients in kale-grown soils

Current organic fertilizers are manufactured from imported ingredients, leading to unstable nutrient supply and high price fluctuations.These issues act as factors that hinder the use organic fertilizers, so in order to promote sustainable agriculture, it is necessary to domestically produce ingredients.In this study, the feasibility of substituting imported ingredients was evaluated by blending biochar derived from spent coffee grounds (SCGs) into organic fertilizers and applying it to kale-grown soils.To manufacture the SCGs biochar-based organic fertilizers, SCGs were pyrolyzed at 600℃ for 0.5 h, and the resulting biochar was mixed with soybean-meal and rice bran.Additionally, the SCGs biochar-based organic fertilizers were categorized based on the ratio of the SCGs biochar content (20 -50%).The content of the SCGs biochar in organic fertilizer showed a positive correlation with the soil chemical properties, including soil pH, carbon, and organic matter content.However, the available nitrogen and potassium contents did not vary with the SCGs biochar content in organic fertilizer.This indicates that the SCGs biochar does not supply nutrients to the soil directly, while improving the soil chemical properties.Nonetheless, the kale yield was highest with the organic fertilizer containing 50% of the SCGs biochar at 5.18 Mg•ha -1 , which was 1.42-fold higher than the kale yield in untreated soil.Thus, increasing the content of the SCGs biochar in organic fertilizer effectively enahced kale yield by improving soil chemical properties.These findings suggest that the biochar could potentially substitute the imported ingredients in organic fertilizer, which often lead to price volatility and inconsistent quality.