2018 ASHS Annual Conference

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 sourced soil amendments. Several new and novel soil amendments, including effective microorganisms (EM1), 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. SPAD readings positively correlated to leaf N content with the highest r² of .74 occurring in March of 2018. SPAD readings showed cyclical fluctuations with a negative trend in spring and a positive trend in summer throughout the year-long experiment. Husk+EM1 and soil profiling 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+EM1 applications had greater mean total root weight, proteoid root weight, and a higher mean proportion of proteoid roots than all other treatments after one year. Total soil N was not significantly affected by treatments. Soil nitrate concentrations increased with the husk treatment showing the greatest increase and ammonium levels decreased. Soil pH was not affected by treatments. Soil EC was significantly increased by the husk+biochar treatment. Soil C was also not affected by treatment. Soil profiling may be an option to increase yield in the short term, but if repeated annually could cause loss of plant vigor. Application of mulches have been shown to reduce yields in the short-term, but this is not evident in this study. Husk+EM1 showed the most promising tree health results within one year. A longer term study is necessary to examine the effects of these treatments on tree and soil response variables.