Influence of the application of charred and uncharred spent coffee grounds on soil Carbon and Nitrogen cycles

ABSTRACT Spent coffee grounds (SCG) and derived products have characteristics (high content of carbon and nutrients) that make them potentially useful as soil amendments. To evaluate the impact of SCG and derived products on soil functionality, an incubation (30 days) was performed with a soil amended with different doses (0.5, 1 and 1.75%) of SCG, a biochar produced from SCG at 270 °C (B270) and a hydrochar produced from SCG at 200 °C (H200). During incubation, the following parameters were measured: CO2 and N2O emissions, extractable organic Carbon (EOC), extractable Nitrogen (EN), NO3 − and NH4 +, microbial biomass Carbon (BC) and Nitrogen (BN). Soil amended with the most degradable materials (SCG and H200) showed greater amounts of CO2, BC and EOC, but also N immobilization. B270 was the most efficient amendment for the retention of added C and led to less N immobilization when compared with SCG and H200. SCG derived amendments can fulfil different functions in soil: SCG and H200 are more indicated for increasing C mineralization and microbial pool, while B270 is more effective at enhancing organic C levels. Higher rates of application generally led to more positive impacts on soil functioning, with the only limitation being short-term N immobilization.