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）是经农工业废弃物热解制备得到的材料，现已成为改善土壤质量最具潜力的管理手段之一。本研究旨在探究将不同咖啡废弃物来源的生物炭施入玉米种植的砂质土壤后，对土壤化学与微生物特性的影响。本实验采用2×3+1析因设计，设置2种生物炭类型：咖啡渣（coffee ground, CG）与咖啡壳（coffee husk, CH），各设置3个施用量（4、8、16 t·ha⁻¹），另设仅施用3 t·ha⁻¹牛粪的施肥对照组。本研究测定的指标包括土壤有机碳、土壤化学特性、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）。研究发现，咖啡壳生物炭（CH）的施用可显著提升多数土壤化学指标；施用量为8 t·ha⁻¹的咖啡渣生物炭（CG）可使土壤C:N比提升至原水平的3.5倍、磷素提升2.1倍、钾离子（K+）提升7.9倍；施用量为4 t·ha⁻¹的CG则可提升土壤碳含量、微生物生物量碳与氮，提升幅度分别为原水平的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（CG）对细菌、真菌与固氮菌基因丰度的提升呈正向趋势，增幅分别为11%、10%与2%。整体而言，两种咖啡源生物炭的施用效果均优于仅施用有机肥的对照组，其中咖啡壳生物炭（CH）的效果更为突出。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技术手段。