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Craig M. Hardner, Marisa Wall and Alyssa Cho

Macadamia is a rapidly developing global crop; however, limited cultivation history and size of the industry means many challenges remain to support sustained productivity and profitability of this industry. This paper summarizes oral and poster presentations, and subsequent papers included in this volume, delivered at the 2017 International Macadamia Research Symposium, held in Hilo, HI, in September of that year. This was the first international meeting of macadamia researchers since 1992. The 28 oral and seven poster presentations covered propagation technology, tree physiology, soils and nutrition, pollination, pest and disease, orchard management, genetics and breeding, product development, and new production regions. Notable messages were that micrografting of macadamias is commercially viable; planting density and girdling could increase early yield per hectare; resource availability may limit cross-pollination yield; and yield production of individual branches is not independent. Integrated pest management was described to develop pest-resilient farming systems and manage felted coccid; an international collaborative approach was proposed for effective disease management and early detection; and the concept of integrated orchard management was used to translate research outputs into a common language for grower adoption. In the areas of breeding and genetic resources, research demonstrated that modern macadamia cultivars are two to four generations from wild but do not capture all wild diversity; progress was reported on the Macadamia Genome Project to produce the first macadamia reference genome; and advances in phenotypic selection and cultivar development were described.

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Alyssa H. Cho, Alan W. Hodges and Carlene A. Chase

Partial budget analyses of five summer fallow treatments in Florida preceding a cash crop of summer squash (Cucurbita pepo) were conducted. The five treatments were sunn hemp (Crotalaria juncea), velvet bean (Mucuna deeringiana), cowpea (Vigna unguiculata), sorghum-sudangrass (Sorghum bicolor × S. bicolor var. sudanense), and tillage. Costs were estimated for each summer fallow treatment, including the cost of seed, inoculant, implementation, management, and termination. Benefits were calculated in terms of contributions to the following cash crop of summer squash in the form of biologically fixed nitrogen and reduced weed pressure. Results showed that total production costs were minimized by cover crops, even though implementation costs were higher than for tillage.

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Russell Galanti, Alyssa Cho, Amjad Ahmad and Theodore Radovich

Macadamia (Macadamia integrifolia, Maiden & Betche) orchard management in Hawaii can result in the loss of organic matter and soil degradation. The objective of this study was to determine the effects of macadamia husk mulch, husk mulch combined with biochar, husk mulch combined with effective microorganisms (EM), soil profiling, and wood chip mulch on yield, nut quality, root growth, and SPAD values during a 1-year study of mature macadamia orchards at two locations in Hawaii. A partial cost–benefit analysis was performed to compare the costs and yield benefits of each treatment. Soil profiling resulted in higher yields than any other treatment, at a mean of 86.6 kg wet-in-husk per tree. No treatments significantly affected nut quality or dry kernel weight. Nut quality was affected by harvesting time, with the earliest harvesting (Aug. 2017) period resulting in the highest recovery rate of number 1 grade kernels (33%). SPAD values increased with the husk mulch combined with EM (6.5%) treatment and soil profiling treatment (6.9%). Husk combined with EM caused an 87% increase in total root biomass during the study period due to increased proteoid root biomass. The soil profiling treatment had the second lowest estimated cost per hectare and had the highest estimated partial profit per hectare. Soil profiling is a destructive management practice and should be used judiciously until its long-term effects on orchard health are studied. The inoculation of EM or sugar signaling may have been responsible for the proliferation of proteoid roots with the husk mulch and EM treatment.

Open access

Russell Galanti, Alyssa Cho, Amjad Ahmad and Javier Mollinedo

Nitrogen (N) management in macadamia (Macadamia integrifolia) orchards is an important concern for growers. Leaf tissue analysis is the accepted method for determining N status in macadamia; however, this process is expensive and time-consuming. The chlorophyll meter has been used in other crops to estimate N status in plants through estimation of the amount of chlorophyll in leaf tissue. The use of the chlorophyll meter in two macadamia cultivars (Kakea and Kau) at two locations in Hawai’i (Kapa’au and Pahala) and five time periods (12 Apr. 2017, 13 June 2017, 15 June 2017, 18 Dec. 2017, and 20 Feb. 2018) was assessed. Leaf samples were collected based on a tissue-sampling protocol, chlorophyll meter (SPAD) values were collected, and leaves were analyzed for total N concentration. Data were analyzed statistically using linear regression. Leaf tissue N concentration had a positive monotonic relationship to SPAD values for both macadamia cultivars, both locations, and all sampling periods. The sampling period of Apr. 2017 for ‘Kakea’ macadamia had the greatest R 2 value for the linear regression at 0.85. The Feb. 2018 sampling period had an R 2 value for the linear regression of 0.74. ‘Kau’ macadamia had the greatest R 2 value for the linear regression of 0.24 in the Dec. 2017 sampling period. The slopes of the two macadamia cultivars for June 2017 were different from each other, suggesting that N recommendations need to be customized for specific macadamia cultivars if sampled in summer. The chlorophyll meter can be used for general estimation of tissue N in macadamia. Additional methods need to be considered and researched to refine procedures for direct estimation of total N concentration when using the chlorophyll meter.

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Noa K. Lincoln, Theodore Radovich, Kahealani Acosta, Eli Isele and Alyssa Cho

Breadfruit (Artocarpus altilis) cultivation is gaining momentum throughout the tropics due to its high yield and nutritious fruit. One impediment to expanding production of breadfruit is the lack of agronomic research related to production management. We examined foliar nutrient concentrations of different leaf positions and leaf parts to assess within- and between-tree variance to inform an effective sampling protocol. We further validated the sampling protocol on 595 trees at 87 sites that were assessed for yield and productivity. Foliar nutrients differed significantly by categories of productivity. For the first time, breadfruit-specific standards of foliar nutrient concentrations are presented for consideration. In conclusion, we recommend that foliar sampling use petioles harvested from leaves in the third position from the branch tip using sun-exposed leaves in the midcanopy of each tree.

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Alyssa H. Cho, Carlene A. Chase, Danielle D. Treadwell, Rosalie L. Koenig, John Bradley Morris and Jose Pablo Morales-Payan

A field study was conducted in 2008 and 2009 in Citra, FL, to evaluate the effects of seeding rate and removal of apical dominance of sunn hemp (Crotalaria juncea L.) on weed suppression and seed production by sunn hemp. Three seeding rates of sunn hemp were used: a representative seed production rate of 11 kg·ha−1, an intermediate seeding rate of 28 kg·ha−1, and a cover crop seeding rate of 45 kg·ha−1. Cutting the main stem at 3, 4, or 5 weeks after planting to break apical dominance was compared with an uncut treatment. Cutting had no significant effect on shoot biomass, photosynthetically active radiation (PAR) penetrating the canopy, and nondestructive leaf area index (LAI). As a result, cutting also had no effect on weed density and biomass in 2008 and very little effect in 2009. Increase in seeding rate resulted in linear decrease in PAR and increase in LAI in both years. Seeding rate had a greater effect on suppression of weed biomass than on suppression of weed density. There was a linear decline in sunn hemp branching with increased seeding rate in 2009 and, averaged across years, flower number decreased linearly with increased seeding rate. Cutting to break apical dominance induced branching but had no effect on flower number. No seed pod production occurred and we postulate that the lack of seed production may be the result of the absence of effective pollinators in fall when short-day varieties of sunn hemp flower in Florida.