The accumulation of coffee pulp as agricultural waste poses significant environmental challenges, including greenhouse gas emissions, water pollution, and land degradation. With rising global coffee demand, effective waste management is critical. A study published in Cleaner Waste Systems by Piyaphad Ninlaphong, Kesinee Iamsaard, Sasiprapa Kullachonphuri, and a team of authors, investigates the potential of converting this waste into biocharBiochar is a carbon-rich material created from biomass decomposition in low-oxygen conditions. It has important applications in environmental remediation, soil improvement, agriculture, carbon sequestration, energy storage, and sustainable materials, promoting efficiency and reducing waste in various contexts while addressing climate change challenges. More using a traditional kiln method to enhance agricultural soil health. The coffee pulp biochar was characterized and then applied to soil at five different rates: 0%, 2.50%, 3.75%, 5.00%, and 7.50% of the soil’s weight. This research explored the effect of these application rates on soil physicochemical properties and microbial activity over a 98-day period.

Characterization of the traditional kiln-produced coffee pulp biochar revealed a pHpH is a measure of how acidic or alkaline a substance is. A pH of 7 is neutral, while lower pH values indicate acidity and higher values indicate alkalinity. Biochars are normally alkaline and can influence soil pH, often increasing it, which can be beneficial More of 9.77±0.01 and a high carbon (C) content of 66.60%±6.50%. Critically, the biochar also contained an abundance of exchangeable potassium (K) at 9.69%±0.12%, which was the most dominant exchangeable cation. Surface morphology analysis confirmed a porous, honeycomb-like structure with pore sizes measured up to 33.90μm and 25.14μm, suggesting good potential for water and nutrient adsorption. Fourier-transform infrared spectroscopy (FTIR) confirmed the presence of various surface functional groups, including C−O stretching and O−H stretching vibrations, which are important for chemical interactions in the soil.

The application of coffee pulp biochar significantly and proportionally increased soil exchangeable K-levels across all tested dosages, except for the control, which is directly attributed to the high K content in the as-made biochar. Conversely, available P content decreased across all treatments over the 98 days, likely due to the biochar stimulating microbial growth, which can immobilize phosphorus. For soil organic matter (SOM), a significant increase was observed only at the 3.75% dosage, while the highest dosage of 7.5% caused a statistically significant reduction in SOM. This suggests that an excessive amount of biochar may saturate the SOM or introduce inhibitors, negatively impacting organic matter decomposition.

In terms of soil biological properties, Soil Microbial Respiration (SMR) and Dissolved Organic Carbon (DOC) increased proportionally with the biochar dosage, with the 7.5% treatment showing the highest increase in both parameters. This is supported by a strong positive correlation between exchangeable K and DOC (r=0.95) and between SMR and DOC (r=0.84). However, Microbial BiomassBiomass is a complex biological organic or non-organic solid product derived from living or recently living organism and available naturally. Various types of wastes such as animal manure, waste paper, sludge and many industrial wastes are also treated as biomass because like natural biomass these More Carbon (MBC) exhibited an inverse relationship, decreasing as the biochar dosage increased, with the 7.5% treatment having the lowest MBC. The reduction in MBC alongside rising SMR may indicate enhanced carbon metabolism but reduced microbial populations, potentially due to excessive metabolic activity. The microbial population analysis further revealed that while moderate dosages (2.50% to 5.0%) significantly enhanced bacteria and actinomycetes populations, the 7.5% dose caused a drop in the total count of bacteria, actinomycetes, and fungi to levels lower than the control. Similarly, cellulase-producing and phosphate-solubilizing microorganisms were enhanced at the 2.5% dosage (by 39% and 14% respectively, compared to the control), but were reduced at the 7.5% rate. This evidence strongly suggests that moderate levels of coffee pulp biochar beneficially impact soil health, while higher application rates, specifically 7.5%, may have adverse, inhibiting effects on certain beneficial microorganisms and overall microbial biomass.

Source: Ninlaphong, P., Iamsaard, K., Kullachonphuri, S., Soilueang, P., Chromkaew, Y., Nakdee, M., Uttarotai, T., Chen, Y., & Khongdee, N. (2025). Physicochemical characterization of coffee pulp-derived biochar and its effects on soil abiotic and biotic properties. Cleaner Waste Systems, 12(100341), 553–571.