Abstract
Heavy applications of gypsum, lime and dolomite, and magnesite and macadamia husk mulch were applied, either alone or as a fertilizer and mulch combination to the soil of eight-year-old variety H2 and variety 508 macadamia (Macadamia integrifolia) trees with decline symptoms and low yields. Decline symptoms, trunk area, yield, leaf and soil nutrient concentrations, and soil physical status were observed over five years. Within one year, trees on mulched soil had a greatly increased fibrous root system and variety H2 showed significantly less decline compared to trees without mulch. There was no effect of Ca and Mg treatments on trunk area or yield. Significant yield increases were recorded for mulched trees of variety H2 in most years and averaged 65%, whilst the response by variety 508 was delayed, averaging 25%. Mulch increased yields similarly for both healthy trees and trees with severe decline. It significantly increased K, Ca, and P concentrations, organic matter, field capacity, permanent wilting point, and available moisture of the 0-15 cm soil depth. Mulch increased leaf P significantly, but the concentration was still sub-optimal; other major leaf nutrient concentrations were not affected by either mulch or Ca and Mg fertilizers. Whilst mulch increased yield, it significantly reduced mean kernel weight, % kernel recovery, and % first-grade kernel due to higher % of mould-infected kernel.
