The Small Tree High Productivity Initiative - Researching the Shape of Future Mango Orchards

Dr Ian Bally, Dr Paula Ibell and Peter Rigden (Department of Agriculture and Fisheries, Queensland)

The Small Tree High Productivity Initiative is a Queensland Department of Agriculture and Fisheries (DAF) and Queensland Alliance for Agriculture and Food Innovation which is co-funded by Horticulture Innovation Australia to develop high density and high productivity orchard systems. The research team is diverse with plant physiologists, plant breeders, geneticists, molecular biologists, and plant modellers working from sites at Brisbane and Mareeba.

The project was inspired by the large gains in productivity achieved by some temperate tree crops over the last 30-40 years. Apple is a standout example with commercial yields increasing from 10-15 tonnes/ha in the 1980’s to 60-100 tonnes/ha for modern, high density orchard blocks today.

The project focuses on four key areas of research that limit productivity of mango orchard:

  • Vigour management - understanding how to effectively manage the tree’s vegetative vigour using rootstocks, pruning strategies for canopy manipulation and growth regulators.

  • Canopy architecture - understanding natural patterns of vegetative growth, flowering and fruiting and the potential to manipulate these through pruning and/or training to optimise the orchard light environment.

  • Canopy light relations - quantifying the role of light in flowering and fruiting and the optimisation of pruning and training systems to maximise productivity.

  • Crop load - developing an understanding of the physiology of crop load and the ability to effectively manage crop load through ensuring adequate flowering and fruit set and subsequent management to maximise yields

Mr Ram Kolala, Horticultural Technician working in the high density trellised tree experiment at Walkamin.

Mr Ram Kolala, Horticultural Technician working in the high density trellised tree experiment at Walkamin.

The overall aim of the project is to develop sufficient scientific understanding and management strategies of these key areas to put them together into a practical system that can be adopted by growers.

It has been a busy first 15 months for the mango ‘small tree’ team in Mareeba who welcome two new team members to the project, Ram Kolala, Horticultural Technician and Anahita Mizani, PhD student with the University of Queensland.

Ram has a B.Sc. in agriculture and M.Sc. in plant physiology. He has managed tissue culture laboratories in Australia and India, and worked as an agronomist in the fresh cut flower industry.

Anahita has completed a Horticultural M.Sc. in apple rootstocks, vegetative characters, fruit quality and fruit set at the Seed & Plant Improvement Institute in Iran.

PhD student Anahita Mizani assessing the fruit quality of fruit from a crop load experiment in Mareeba.

PhD student Anahita Mizani assessing the fruit quality of fruit from a crop load experiment in Mareeba.

Vigour management with rootstocks

Reducing mango tree vigour and diverting energy into production is critical for sustainable high yields. Very few rootstocks are known to reduce tree vigour in mango and those that do only work on one or two scion varieties. The project has begun to look for new rootstocks that will reduce vegetative vigour while still providing high yields and sound fruit quality that can perform in high density mango orchard systems.

Testing over 90 rootstocks with potential to reduce tree vigour in high-density situations has begun. The first 30 were grafted and field planted in mid and late 2014 with another 60 to be planted over the next 18 months. We may detect the first signs of vigour control in the next 12 months but it is likely that effects may not be apparent until the trees begin regular cropping at two to three years old.

Canopy architecture and training

NMBP1243 trained onto a trellis at 14 months after planting

NMBP1243 trained onto a trellis at 14 months after planting

New ways of training and pruning mangoes are being investigated to optimise light, manage vigour and reduce pruning in high density orchards systems. A “Planting Systems” field experiment was set up in December 2013 to investigate how the three mango varieties Keitt, Calypso and NMBP1243 respond to three planting densities (156, 440 and 1250 trees per ha). Canopies are being trained to either conventional, single leader or hedged architectures. At the highest planting density, the single leader canopies are either supported by trellises or hedged.

Keitt being trained as a single leader canopy. Limbs are being tied to the red blocks to make the scaffold branches grow horizontally from the central leader to reduce tree vigour.

Keitt being trained as a single leader canopy. Limbs are being tied to the red blocks to make the scaffold branches grow horizontally from the central leader to reduce tree vigour.

Since establishment the trees have been regularly pruned to establish the three canopy architecture styles and precise measurement of growth and architecture have been made. Although some trees flowered in September last year, flowers were removed to encourage canopy development. When trees mature, this experiment will allow us to determine which varieties are most suited to high density production by measuring their light relations, flowering, yield and biennial variability.

Canopy light relations

Shade from a Kensington Pride mango orchard indicating the light intercepted by the canopy at midday

Shade from a Kensington Pride mango orchard indicating the light intercepted by the canopy at midday

The project team is studying the relationships between light, canopy architecture, productivity and fruit quality. Total light interception is the amount of light falling on a hectare that the tree canopies intercept. Light energy intercepted by the canopy is converted to biomass during photosynthesis and this influences yield. Understanding light relationships will help to determine the best plant spacing and canopy training options for high density mango orchards that can produce high quality fruit.

Relationship between light interception and canopy volume per hectare in Kensington pride, showing maximum interception of 68% at 13,300 cubic meters per hectare

Relationship between light interception and canopy volume per hectare in Kensington pride, showing maximum interception of 68% at 13,300 cubic meters per hectare

A baseline study of the total light interception has started on seven farms in the Mareeba and Mutchilba districts, on Kensington Pride orchards of varying planting configurations, age and pruning systems. Light interception was compared with tree age, canopy characteristics and yield.

The early findings of this study have found that on average, light interception reached its maximum of 68% in KP trees up to approximately 25 years old. The percentage light interception is the amount of light intercepted by the tree canopy within its allocated space in the orchard, including the inter-row. This is an average of 50 measurements taken five times a day on a cloud free day using a ceptometer, an instrument that is used to accurately measures light levels. As the canopy volumes increased so did light interception with the maximum interception of 68% occurring when the canopy volume reached 13,300 cubic meters per hectare. These trees formed a continuous canopy along the row and just had space for a tractor to pass between rows.

Relationship between light interception and yield in tonnes per hectare in Kensington pride, showing maximum yields are reached at about 68% light interception.

Relationship between light interception and yield in tonnes per hectare in Kensington pride, showing maximum yields are reached at about 68% light interception.

Yields increased up to 50% light interception, after which the increase in yields slowed with maximum yields being reached at 68% light interception.

This baseline study will continue to measure light interception in some additional orchards, as well as begin to study the distribution of light within the canopy.

In future these light relations will be compared with similar measurements from the “Planting Systems” field experiment to compare their efficiency with current orchard systems. The “Planting Systems” experiment will investigate how to optimise light interception in younger trees and therefore reach maximum yields earlier in an orchard’s life.

The project team thank growers who participated in this work and are looking for additional 10 to 25 year old orchards to measure in the Mareeba and Dimbulah district.

Crop Load

Calypso trees used in the crop load study with 100% flowering (no flowers removed.

Calypso trees used in the crop load study with 100% flowering (no flowers removed.

A multiyear study to investigate the effects of crop load on subsequent yield, canopy growth and flowering with the aim of managing crop load to reduce irregular and biennial bearing has begun. In the past year an experiment started that aims to study the effect of different percentages of flowering terminals on the current and subsequent years productivity and fruit quality.

The experiment was conducted on the cultivar Calypso and involved manipulating the number of flowering terminals by removing flowers to provide trees with a range of flowering percentages. Early findings, based on one season of study, are indicating that Calypso mangoes have a strong ability to compensate for poor flowering.

Essentially, on average there was no yield reduction between trees with 100% and 10% flowering as trees tended to compensate. The fruit number per tree at harvest was similar from full flowering down to 10% flowering. Average fruit weight remained consistent from full flowering to about 30% flowering, below which average fruit weights increase by approximately 15%.

Calypso trees used in the crop load study with 10% flowering (90% flowers removed.

Calypso trees used in the crop load study with 10% flowering (90% flowers removed.

The tree also compensated for lower flowering percentages by retaining more fruit per panicle. Trees with greater than 30% flowering had in average one fruit per panicle, whereas trees with less than 30% flowering retained two or more fruit per panicle. The percentage of flowering did not affect fruit maturity at harvest. A second year of observations is needed before any conclusions can be made about any effects on biennial bearing. It is likely factors such as tree nutrition, health and cultivar may cause trees to respond differently to reduction in percentages of flowering.

Future reports on the small tree high productivity initiative will focus on some of the other research activities in the project such as the molecular regulation of flowering and canopy growth and some of the architectural and growth modelling techniques being used to predict how mangoes respond to growing at high density.

Acknowledgments  

It has been an incredibly busy year for us and we would like to thank all growers who have participated in these experiments. We will continue to report on results in future editions of Mango Matters.

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Please contact us at DAF at Mareeba on 07 4048 4600, if you are willing to have your KP orchard involved in the light interception trial work or if you would like more information about any of the trails.

We would also like to acknowledge the researchers who have contributed to the work presented in this article including Ian Bally, Paula Ibell, John Wilkie, Jim Hanan, Ram Kolala, Cheryl Maddox, Anahita Mizani and Carole Wright.

The Small Tree High Productivity Initiative is an initiative of the Queensland Government, which focuses on improved productivity of mango, macadamia and avocado. Major partners include the DAF, DAF’s research alliance with The University of Queensland (Queensland Alliance for Agriculture and Food Innovation), and the NSW Department of Primary Industries.

This project has been funded by Horticulture Innovation Australia Limited using the Across Horticulture levy with co-investment from the Queensland Department of Agriculture and Fisheries, and funds from the Australian Government. We are especially grateful to HIA and the various associated industries and horticultural businesses for their support for this project.