Mineralization potential of spent coffee grounds and other nutrient sources

Industrial-scale coffee ground waste has the potential to serve as a nutrient-rich soil amendment, which would offer growers an opportunity to reduce applications of traditional fertilizers. Composted spent coffee grounds (CSCGs) and noncomposted spent coffee grounds (NCSCGs) were evaluated for their potential as organic N fertilizers. Nitrogen mineralization of NCSCGs and CSCGs was compared to commonly used synthetic and organic N fertilizers: urea and Milorganite. Net N mineralization and microbial activity were measured in a fine sandy loam field soil at 25°C and 60% water holding capacity weekly for 100 days. Despite a C:N of 13:1, the CSCGs appeared to have slow mineralization. Total inorganic N was lower in both CSCGs and NCSCGs than the control throughout the 100-day incubation with no additional N to the system. Greater CO₂─C respiration was recorded with SCGs, suggesting microbial activity is required for the breakdown of SCGs relative to other treatments. CSCGs may serve as a long-term fertilizer due to the time it takes to mineralize; however, over a shorter period, it may increase the nutrient- and water-holding capacity of soil, which can improve plant growth.