ORCHARD MULCHING EFFECTS ON AVOCADO FRUITING

The "subtropical" avocado tree evolved in a cool, mesic highland rainforest with a decomposing litter layer, in which its feeder roots proliferate. We reasoned that under more stressful orchard conditions it should benefit from mulching with suitable materials to reinforce the natural dead leaf layer. We also hypothesized that the resultant improved root health and growth would partly ameliorate the 'Hass' small fruit syndrome, which is associated with "stress". An ongoing mulching trial with composted pine bark in the cool, mesic summer rainfall mistbelt of KwaZulu-Natal has led to an average increase form mulching (over 3 seasons) of 7% in fruit size, 15% in fruit number and 23% in yield. Mulching reduced measured components of tree stress, including a lowering of leaf canopy temperature, photoinhibition of photosynthesis, premature seed coat abortion and pedicel ringneck. Phenotypically small fruits were higher in flesh abscisic acid and lower in cytokinins. However mulching amelioration of stress does not explain all aspects of the small fruit phenotype. Mulching with suitable materials has additional benefits in most orchard situations, but pros and cons (including availability, cost, C:N ratio, rapidity of decomposition) must be understood and tailored to particular orchard environments and conditions.

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