Coffee processing residues as a soil potassium amendment

Introduction Total coffee production in the world in 2013was 8.7 million Mg of coffee beans. Coffee must be processedafter harvest to separate beans from the husk, andthe post-harvest process can generate different types ofresidues. Knowing that 50 % of the harvested coffee ishusk, it is important to consider that these by-products cancontribute to environmental problems if not disposed ofproperly. There is a need to find alternatives to the piling ofcoffee husk as a means of disposal at coffee farms. Theobjectives in this experiment were to characterize fivetypes of coffee processing residues and assess their valueas potassium (K) fertilizer by examining K release.Results Chemical characteristics of coffee residues variedwith processing method, such as wet and dry processes.Application of residues to soil columns followed by40 weeks of simulated leaching increased total K contentin the soil for all treatments based on application rate,except for enriched and three-year composted coffee husk(3ycomp). Coffee processing residues had higher concentrationsof K leached compared with the control with no Kapplication, but only 3ycomp was higher than other coffeeprocessing residues. Total K released from coffee residuesincreased linearly with application rate, but the decompositionof the coffee residues was low, which suggest that Krelease from coffee processing residues is not related todecomposition.Conclusion Post-harvest coffee processes impacted concentrationsof K, nitrogen, carbon, cellulose, hemicellulose,lignin, phenol, pH, and electrical conductivity among thecoffee processing residues. The K release was high (over90 %), but it did not depend on the type of coffee processingresidue, and thus, the residues can be a substitutefor a mineral source of K applied to soils. The use of coffeeprocessing residues as source of K did not prevent K lossesby leaching. Some coffee residues resulted in greater Kleaching than mineral KCl applied at the same rate.