Coffee waste as an eco-friendly and low-cost alternative for biochar production impacts on sandy soil chemical attributes and microbial gene abundance

ABSTRACT Biochar is a material produced by the pyrolysis of agro-industrial waste, which has become one of the most promising management tools to improve soil quality. The aim was to determine the effects of incorporating biochar from different coffee wastes in sandy soil, cropped with maize, on soil chemical and microbial attributes. The experiment followed a factorial design 2 × 3 + 1 with two types of biochar, including coffee ground (CG) or coffee husk (CH) in 3 doses (4, 8, and 16 t·ha-1) and a control fertilized solely with bovine manure (3 t·ha-1). The variables analyzed were soil organic carbon, chemical attributes, microbial biomass (C, N and P), soil basal respiration and microbial gene abundance (16S rRNA, 18S rRNA and nifH gene). Most chemical attributes were strongly increased by CH application, while CG at 8 t·ha-1 increased the soil C:N ratio (3.5 times), P (2.1 times) and K+ (7.9 times) and at 4 t·ha-1 increased the C content, microbial biomass C and N (3, 2.1 and 1.6 times, respectively). The application of CG biochar at 16 t·ha-1 showed trend to increase the abundance of bacteria, fungi and diazotrophic genes (11, 10 and 2%, respectively). Contribution of both coffee biochar types, but mainly CH, was more effective than the soil that received organic manure alone. Biochar from coffee wastes is a promising tool to improve sandy soil quality.

摘要 生物炭（biochar）是一种通过农工业废弃物热解制备的材料，现已成为改善土壤质量最具潜力的管理手段之一。本研究旨在探究不同咖啡废弃物来源的生物炭施入玉米种植砂质土壤后，对土壤化学与微生物特性的影响。本实验采用2×3+1因子设计，设置2种生物炭类型，即咖啡渣（coffee ground, CG）与咖啡果壳（coffee husk, CH），3种施用量（4、8、16 t·ha⁻¹），并设置仅施用3 t·ha⁻¹牛粪肥的对照组。本研究测定的指标包括土壤有机碳、土壤化学属性、微生物生物量（碳、氮、磷）、土壤基础呼吸速率，以及微生物基因丰度（16S rRNA、18S rRNA与nifH基因）。研究结果显示，咖啡果壳生物炭的施用可显著提升多数土壤化学属性；施用量为8 t·ha⁻¹的咖啡渣生物炭可使土壤碳氮比提升3.5倍、磷含量提升2.1倍、钾离子（K+）提升7.9倍，施用量为4 t·ha⁻¹时则可使土壤有机碳含量、微生物生物量碳与氮分别提升3倍、2.1倍与1.6倍。当施用量为16 t·ha⁻¹时，咖啡渣生物炭对细菌、真菌与固氮菌基因丰度分别呈现11%、10%与2%的提升趋势。两种咖啡源生物炭的施用效果均优于仅施用牛粪肥的土壤，其中尤以咖啡果壳生物炭的效果更佳。综上，咖啡废弃物来源的生物炭是改善砂质土壤质量的极具潜力的手段。