Transforming sub-tropical and tropical tree crop productivity (AI13004)

What was it all about?

This investment adapted the principles and management systems developed for orchard intensification of temperate tree crops, such as apples, for extensive orchard systems of subtropical and tropical tree crops. Avocado, macadamia and mangoes were selected as the focus of this work due to high potential for improved productivity.

The key components of modern apple orchard systems that allow them to be so productive are orchard light relations, vigour management, crop load, and tree and shoot architecture. In this investment, efforts were made to improve understanding of these key components for avocado, macadamias and mangoes, so that alternative management options could be developed for those crops. The project team used applied field experiments, molecular genetics and plant modelling to conduct their research.

A major focus of the program was large-scale planting systems trials for each crop, where investigations occurred at how the key components interacted with each other at different tree planting densities, scion varieties, rootstocks, and tree training systems.

Key findings for each crop have been summarised below.

Mango

Fundamental relationships between total light interception and orchard yields, and between inflorescence density and yield efficiency were established. By intensifying mango orchard systems, total light interception was increased during early orchard life, leading to increased early yield per hectare, particularly for the precocious varieties. At the high-density of 1,250 trees per hectare, trellised ‘Keitt’ and ‘Calypso’ yielded 53 and 43 tonnes per hectare, respectively, five years after planting.

Macadamia

Selective pruning in a Bundaberg commercial macadamia orchard produced greater nut-in-shell yield than the industry standard mechanical hedging and topping. As with mango, intensive planting systems in macadamia had greater canopy volume per hectare and greater total light interception during early orchard life. This led to higher and earlier orchard yields in the precocious flowering variety ‘A203’, which at 5 years of age, when planted at high density (1,000 trees per hectare) produced 4.9 t per hectare nut in shell compared with 2.9 t per hectare for the low density (312 trees per hectare).

Avocado

In ‘Hass’ avocado, fundamental relationships between total light interception and yield per hectare, and between inflorescence density and yield efficiency were established. Early in the life of the intensive avocado orchard trial, the canopy volume per hectare and total light interception of the high and medium density systems were greater than the industry standard low-density systems. High-density systems had higher orchard yields two years after planting, however by year five, orchard yields of the low-density industry standard orchard system was significantly greater than when grown at high-density. The lower vigour ‘Ashdot’ rootstock has consistently produced greater yield per hectare than the higher vigour industry standard ‘Velvick’ rootstock in the planting systems trial.