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The Effects of Soil Amendments on Tree Growth, Yield, and Soil Properties in Mature Macadamia Integrifolia Orchards.

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Title:The Effects of Soil Amendments on Tree Growth, Yield, and Soil Properties in Mature Macadamia Integrifolia Orchards.
Authors:Galanti, Russell C.
Contributors:Tropical Plant & Soil Sciences (department)
Keywords:Macadamia
soil amendment
mulch
conservation agriculture
sustainable agriculture
show 2 morebiochar
effective microorganisms
show less
Date Issued:Aug 2018
Publisher:University of Hawaiʻi at Mānoa
Abstract:Current management practices in macadamia production call for the removal of all tree litter 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. Farmers in Hawai‘i have expressed interest in using locally sourced alternative soil amendments. A randomized complete block design was implemented on a ~700 acre macadamia farm in Kapa’au, HI. Two sites were selected, one organically managed (Site 1) and one conventionally managed (Site 2). Four blocks consisting of six treatment plots were identified. Several novel soil amendments, including effective microorganisms (EM1), biochar, and a management practice called soil profiling were identified and were compared to traditional amendments including macadamia husk mulch and wood chip mulch. Including a control treatment, the total treatment amount was six treatments. The effects of these amendments on root growth, SPAD readings, yield/quality in macadamia, and soil carbon (C), nitrogen (N) , pH, and EC were studied. The use of the Minolta SPAD-502 chlorophyll meter to estimate tissue N was evaluated on two macadamia cultivars (HAES 508 ‘Kakea’, and HAES 344 ‘Keaau), and four sampling times (June 2017, December 2018, and February 2018). SPAD readings had a positive monotonic relationship to leaf tissue N concentrations. For cultivar HAES 508, the February 2018 sampling period had an r2 value of 0.74. HAES 344 had the highest r2 (0.24) at the December 2017 sampling period. The Minolta-502 chlorophyll meter can be used for general estimation of tissue N but additional methods need to be considered to refine procedures for direct estimation of N using the chlorophyll meter. Soil profiling resulted in higher yields than any other treatment at a mean of 86.6 kg/tree wet-in-husk. Mean SPAD value was increased by the husk+EM1 and soil profiling treatments from pretreatment values. Husk+EM1 caused an increase in total root biomass over the study period due to an increase in proteoid root biomass and proportion of proteoid root biomass to total root biomass. The soil profiling treatment was the second lowest in estimated cost per acre to apply and was the highest in estimated partial profit per acre. 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 EM1 may have been responsible for the proliferation of proteoid roots under the Husk+EM1 treatment due to microbial inoculation or simple sugar signaling of proteoid root growth. Husk treatments resulted in the greatest increases in NO3- concentrations and the least decreases in NH4+ concentrations. pH was increased at site 2 for the husk, husk+biochar, and soil profiling treatments. EC was increased by the husk+biochar treatment at site 1 by 0.42 mS/cm and all three husk treatments increased soil EC at site 2. Soil C was increased by husk and husk+EM1treatments at site 1. Husk treatments have the potential to increase NO3- while not causing a significant reduction in NH4+ as well as increase soil C. Nitrate is readily leachable from the soil profile, and also requires that the plant expend energy once absorbed. Potential issues with husk mulch use, particularly in combination with biochar or EM1 are increases in pH from 7.7%-10.3% and EC from 66%-100% . While these were statistically significant increases, these increases are not high enough to affect production or plant health after one application. Long term effects of repeated application may cause yield reduction. Mulches generally have more influential effects long-term and results of their effects over a longer period of time would be valuable.
Description:M.S. Thesis. University of Hawaiʻi at Mānoa 2018.
URI:http://hdl.handle.net/10125/62810
Rights:All UHM dissertations and theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission from the copyright owner.
Appears in Collections: M.S. - Tropical Plant and Soil Sciences


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