CCREF Research Reports
Current management practices in macadamia production call for the removal of all tree litter-fall from the orchard floor to facilitate nut pick up during harvesting season, which can be up to 10 months of the year. This and derivative management practices lead to degradation of soil and environmental health and reduced nut production. Hawaiian farmers have expressed interest in sourcing alternative locally developed soil amendments. Several new and novel soil amendments, including effective microorganisms, biochar, and soil profiling, have been identified and were compared to traditional amendments including macadamia husk mulch and wood chip mulch. The effects of these amendments on root growth, SPAD readings, and yield/quality in macadamia and soil Carbon, Nitrogen, pH, and EC were studied. A partial economic analysis was done to determine treatment costs and yield benefits for all treatments. SPAD readings showed cyclical fluctuations with a negative trend into the summer and a positive trend into the winter throughout the year-long experiment. No treatments significantly increased mean SPAD values within the year time frame. Mean total yield was highest for the soil profiling treatment (mean of 86.5 kg/tree). Trees under husk mulch+effective-microorganism applications had greater mean proteoid root weight and a higher mean proportion of proteoid roots than all other treatments after one year. Soil profiling had the greatest revenue and partial profit due to its high yield compared to the other treatments. Mean pH, soil C and N proportions, and nitrate concentrations were not significantly affected by treatment. All husk treatments and the soil profiling treatment caused significant increases in mean soil EC. The husk+biochar treatment plots had significantly higher mean EC than all other treatment plots in February 2018 with the exception of the other husk treatments. All treatment plots resulted in a reduction in mean ammonium concentrations from August 2016 to February 2018 but only the control, soil profiling, and wood chip treatment plots had significant reductions. This also meant the husk treatment plots had significantly higher mean ammonium concentrations in February of 2018. Soil profiling may be an option to increase yield in the short term, but if repeated could cause loss of plant vigor. Application of mulches have been shown to reduce yields in the short-term, but this is not supported by this study. Longer term data collection of yield would be beneficial to determine the relationship between the discussed plant and soil parameters on long term yields.