A recent study published in Cleaner Waste Systems, authored by Piyaphad Ninlaphong, Kesinee Iamsaard, Sasiprapa Kullachonphuri, Phonlawat Soilueang, Yupa Chromkaew, Metinee Nakdee, Toungporn Uttarotai, Yaoliang Chen, and Nuttapon Khongdee, explores the effectiveness of coffee pulp-derived 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 as a sustainable solution for improving agricultural soil health. The research investigates its influence on soil nutrient content, physicochemical properties, and microbial activity, focusing on biochar produced using traditional kiln methods, which are accessible to smallholder farmers.

The study characterized the coffee pulp biochar, revealing a high carbon (C) content of 66.60% and an abundance of exchangeable potassium (K). Scanning electron microscopy (SEM) showed diverse pore structures, including a honeycomb-like matrix, with pore sizes measured at 33.90 µm and 25.14 µm. Fourier-transform infrared spectroscopy (FTIR) identified various functional groups, such as C-H, N-H, C-O-C, and O-H stretching, indicating a chemically active surface. The biochar itself was alkaline, with 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 and an electrical conductivity (EC) of 0.24 dS m−1. The traditional kiln method yielded approximately 40-45% of biochar from the total dry weight of coffee pulp.

The researchers assessed the impact of incorporating coffee pulp biochar into soil at various proportions: 0, 2.50, 3.75, 5.00, and 7.50% of the soil’s weight. The analysis of basic soil nutrients revealed statistically significant differences in several parameters. Available phosphorus (P) decreased proportionally with increasing biochar application from 55 to 98 days. This reduction might be due to biochar stimulating microbial growth, which could immobilize P and thus reduce its availability. Soil organic matter (SOM) showed a statistically significant increase only at a 3.75% biochar dosage, while a 7.5% application led to a reduction, possibly due to SOM saturation or the introduction of inhibitors that negatively impact microbial activity.

Conversely, exchangeable K in the soil increased proportionally with the percentage of coffee pulp biochar added, with a statistically significant rise observed in all biochar treatments except the control. This is directly linked to the high K content (11.63%) in the coffee pulp biochar itself. Exchangeable calcium (Ca) significantly increased only at a 5% biochar dose, while exchangeable magnesium (Mg) generally decreased across treatments. Soil pH consistently increased with higher biochar dosages, with the most significant rise at 7.5% application, attributed to alkaline substances like calcium carbonate and potassium carbonate within the biochar. Soil EC also tended to increase with higher biochar treatment duration and dosage.

In terms of soil biological properties, soil microbial respiration (SMR) and dissolved organic carbon (DOC) increased proportionally with the percentage of coffee biochar used, with the highest increases observed at 7.5% application. This suggests that coffee pulp biochar acts as a source of organic carbon for microbial metabolism, with microorganisms utilizing DOC for respiration. 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, possibly indicating reduced microbial population during periods of increased metabolic activity or that metabolized carbon did not promptly facilitate new MBC production.

Microbial analysis further revealed interesting shifts in populations. Fungal counts generally decreased in biochar treatments compared to the control, with a maximum reduction of 68% at 5% biochar. Conversely, bacterial and actinomycete populations generally increased, except at the highest 7.5% biochar application rate where all microbial populations dropped below untreated levels. Importantly, at a 2.5% biochar application rate, cellulase-producing microorganisms increased by 39% and phosphate-solubilizing microorganisms increased by 14% compared to the control. This suggests that moderate levels of biochar application can beneficially impact soil microbial populations and enzyme activities, while higher levels may have adverse effects on certain beneficial microorganisms.

The study concludes that coffee pulp biochar from traditional kilns significantly alters soil physicochemical and biological characteristics. Its high exchangeable K content positively correlates with improved soil biological parameters like SMR and DOC. This research contributes to understanding waste management in coffee production and provides insights for future research planning, particularly in evaluating the long-term effects of diverse biochar feedstocks on soil characteristics and their capacity for carbon sequestration and climate change resilience.

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.