Trial demonstrations, observations and measurements in mature macadamia plantations on the Alstonville Plateau
Since mid-1985 the term macadamia decline was used to describe canopy thinning and loss of pre-estimated cropping levels. Trees growing in the rich medium red clay loams of the Alstonville Plateau did not respond to heavy applications of lime to correct low pH levels. Tree health improved with heavy mulch placed under the drip line. This was the first indicator that improved tree health was influenced by reduced soil temperature leading to increased soil biology. Using a penetrometer (used to measure levels of soil compaction) identified the majority of 10- to 20-year-old plantation trees have an average root depth of 125 mm. Measurements indicate canopy size in 15-year-old trees is seven times larger than their root area. An application program of specific anaerobic microbes sprayed underneath the macadamia tree canopy was able to restructure the soil allowing roots to penetrate down to 500 mm plus. Soil porosity improved with increased microbe and fungi levels including the development of Glomalin. A twelve-month application program increased yields by more than 100% in 22-year-old trees.
Gourlay, D.B., King, J.P., Watson, C. and Watson, N. (2016). Trial demonstrations, observations and measurements in mature macadamia plantations on the Alstonville Plateau. Acta Hortic. 1109, 161-164
compaction, erosion, root depth, restriction, macadamia decline, loss of production, microbial diversity