Higher densities could boost fruit yields
GROWERS who plant fruit trees intensively must be prepared to manage those trees intensively, too, if they are to maximise output from their orchards, participants in the technical forum’s ‘New technologies for future plantings’ workshop heard.
Queensland Department of Agriculture and Fisheries (DAF) senior horticulturist Helen Hofman shared that advice as part of her presentation on research into high-density planting of three tropical and subtropical tree crops: avocados, mangoes and macadamias.
Helen told the Citrus Tech Forum and Field Day in March that findings from the Small Tree – High Productivity Initiative could have application in citrus, which as an industry was already embracing the idea of planting more densely.
The ambitious initiative aims to transform the productivity of the tree crops being studied, but it is acknowledged that it may take 20 years to optimise ‘small tree’ systems for all three.
The initiative started with a small initial DAF royalty-funded research project, and continues to be led by DAF in its bigger form today. The current project is funded by Horticulture Innovation Australia using the across-industry levy, with co-investment from DAF, the Queensland Alliance for Agriculture and Food Innovation, and the NSW Department of Primary Industries, plus funds from the Australian Government.
Helen said while citrus was already performing relatively strongly in the tropics and subtropics, the three crops involved in the project were currently “underproductive”, with scope for improvement. “Mangoes, macadamias and avocados are all quite low in productivity,” she said.
Helen said the research aimed to test four methods that had been used effectively in pome and stone fruit:
- Managing tree vigour
- Optimising the amount of light reaching between and within trees
- Manipulating tree architecture to create a traditional “Christmas-tree shape”
- Maximising crop load using strategies such as thinning and/or use of plant growth regulators
“Most citrus growers are currently planting at about 300 trees per hectare,” she said. “We classify that as medium density.
“For our purposes, high density is at least 1000 trees/ha – for example, spacings of 2-2.5m in rows that are 4m apart.”
Helen said the results of past higher density plantings in citrus had varied but often yields per hectare had peaked early before plateauing at the level of low-density plantings at the 7-10-year point. “However, unlike our new initiative, most earlier trials did not attempt to actively manage vigour or optimise light interception and were planted on vigorous rootstocks.”
Helen said a driver for high-density planting was current research on developing -robotic picking, which was most efficient when the machinery was presented with a solid “fruit wall” of the type created by high-density planting.
Other drivers included a shift towards shorter tree life through more rapid turnover of varieties as well as the increasing costs of land, water and labour.