or moderately grow fewer trees with moderate amounts of inputs; or you plant more trees (e.g. 500 to 550 trees/ha) and let the tree numbers do the work rapidly filling the canopy. Roger Duncan has a 14 year old, 15 hectare, tree density trial overlaid with four pruning strategies and two rootstocks. Tree densities range from 222 trees/ha (6.7m x 6.7m) to 489 trees/ha (6.7m x 3.0m). CMV Farms, in their more recent plantings, have tree densities of approximately 357 trees/ha (7.0m x 4.0m), 555 trees/ha (6.0m x 3.0m) and 833 trees/ha (6.0m x 2.0m). Findings from Roger’s trial and CMV’s plantings indicate the following: • In comparison to conventional densities, higher tree densities have a greater water and fertiliser requirement in the earlier years due to increased canopy area and yield.
Figure 1: Almond yield potential relationship with midday canopy PAR interception (Lampinen, 2013).
• Smaller canopies such as Price, Wood Colony, Carmel, etc benefit from tighter spacings. • Large, vigorous trees may not have increased yields, even in the early years. • No yield disadvantage to close spacing of vigorous trees (yet). • Tree size is kept smaller with tighter spacings. • Tighter spacings and smaller tree sizes have benefits of less scaffold splitting, less trunk shaker injury, less replants over the life of the orchard, less impact on yield from trees dying as the quantity of missing canopy or light interception is reduced, less unharvested nuts (mummies), less over-wintering sites for carob moth and hull rot inoculum, better spray coverage, and greater cumulative yield (so far). • Quicker to shake trees, but marginally more expensive due to the higher number of trees. It was also noted by Bruce and Roger that higher density orchards would benefit from north/south row orientations. This would facilitate easier orchard floor drying of harvested fruit and reduced food safety risks. North/south rows are also more likely to facilitate more uniform fruit maturation throughout the tree canopy. To prune or not to prune? A hot topic of discussion over the conference and field days was the benefits of pruning, particularly for the higher density plantings. There was unanimous agreement that pruning should be undertaken for reduced food safety risks and maintenance of access (machinery, weedicide, etc), vision (e.g. shaking) and worker safety. However, the benefits (versus the costs) of pruning for managing light distribution with respect to maximising longevity of fruiting spurs, renewal of fruiting wood, reducing alternate bearing, etc was less convincing or very expensive and you end ‘fluffing around the edges’. Roger’s early conclusions from his pruning trial are: • Pruning has not increased yield but it has however led to increased costs and lower gross margins. • Trees trained to more than three scaffolds are more prone to blow-over, scaffold breakage and consequently you need to rope them.
• Scaffold selection (training) is less important in closely planted trees as trees stay smaller and there’s less weight on each limb. • Slightly more hull rot incidence in unpruned trees.
• No difference observed in other diseases. • No difference observed in stick tights. • No difference in tree height.
Whilst it appears there are several reasons to prune an almond orchard, yield does not appear to be one of them. In fact, non- discriminate hedge pruning leads to a vicious cycle where pruning one limb will produce several limbs and a denser canopy that continually requires maintenance. This continual maintenance performed by hedge pruning decreases the canopy size and quantity of light interception leading to reduced yield. With respect to pruning higher density plantings, it was suggested that other than for reasons of access, vision and worker safety, all other pruning should be minimised and left for as long as possible – capitalising on the natural growth habit of the tree and more varied light and orchard floor temperature patterns. As soon as you begin hedge pruning you will fall into the same vicious cycle mentioned earlier and you could even reduce yield further due to the increased number of rows and consequently increased amount of area removed from production following the hedge pruning. Summary In summary, based on the current availability of knowledge, rootstocks, training systems and management programs neither conventional or higher density orchards are perfect; but it appears higher densities have several advantages and warrant serious consideration, in particular spacings of approximately 6.5m x 3.0m (513 trees/ha). It also needs to be highlighted that regardless of tree densities, food safety requires due consideration at the expense of maximum canopy coverage and light interception.
For further information contact:
Ben Brown Industry Development Manager Almond Board of Australia P 08 8582 2055 or 0447 447 223 E: firstname.lastname@example.org