Mulch Addition Increase Growth, Yield and Soil C and N in a Managed Full-Sun Coffee System in Hawaii.

The objectives of this study were to evaluate the potential of a cut-and-carry system of mulch additions for open-grown coffee in Hawaii, utilizing the multipurpose nitrogen-fixing tree Leucaena variety KX2. A stand of Leucaena-KX2 trees were pollarded every 6 months, and the pollarded material was chipped and added to open-grown coffee plots on an equal-area basis. Approximately 65 Mg ha^‑1 of mulch dry matter was added over a 3-year period, including ~27.5 Mg ha^‑1 of C and ~530 kg ha^‑1 of nitrogen (N). Plots without mulch addition were fertilized with equivalent amounts of inorganic N for comparison. Mulch decomposition averaged 64% over the first year and followed first-order decay dynamics. Net N mineralization was positive by 3 months after addition. There was significant loss of all major biochemical components during the decomposition process. Mulching increased soil carbon dioxide (CO₂) efflux by 0.75 (µmol m^-2 sec^-1). Total soil C and N increased by 2.90 and 1.42 Mg ha^-1, respectively. Mulch addition significantly increased all measures of coffee growth and yield over two years, except for average bean weight. Where space is available or shade is undesirable, a cut-and-carry mulching system using Leucaena-KX2 can increase soil C and N and coffee growth and yield.