Leucaena-KX2 mulch additions increase growth, yield and soil C and N in a managed full-sun coffee system in Hawaii

One option to sustain full-sun coffee plantation is the use of a cut-and-carry system in which a stand of N-fixing trees is grown outside the coffee field and utilized as a source of mulch to capture the benefits of organic matter, nutrient additions, and continuous soil cover. The objectives of this study were to evaluate the potential of a cut-and-carry system of mulch additions from a multipurpose N-fixing tree for open-grown coffee in Hawaii to support high crop yield as well as improved soil organic matter and nitrogen. A stand of Leucaena variety KX2 trees were pollarded every 6 months, and the pollarded material was chipped and added to open-grown coffee plots. Approximately 65 Mg ha(-1) of mulch dry matter was added over a 3-year period, including similar to 27.5 Mg ha(-1) of C and similar to 530 kg ha(-1) of total N. Plots without mulch addition were fertilized with equivalent amounts of inorganic N for comparison. Mulch decomposition averaged 64 % (weight basis) 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 CO2 efflux by 2.89 Mg ha(-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 2 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 achieve coffee yields similar to or greater than other full-sun systems.