POMEWEST preparing for dry conditions
Dry Season
TACTICS
for Orchards
As at 30 June 2024, South West growing regions are between 90 and 185mm below median rainfall for the year. This places 2024 as a decile 1 year, meaning it is in the driest 10% of years from the past 100. There are different strategies for managing orchards through dry seasons.
Words Jennifer Riseley, Project Officer, Pomewest
FROM the millennium drought experienced in the eastern states, many tactics were applied to help orchards manage in the long term.
The following article uses information provided from AgVictoria, APAL Future Orchards Library, Dr Nigel Swarts of the University of Tasmania and DPIRD researchers Neil Lantzke, Kevin Lacey and Simon Yeap.
For young trees or new plantings
1. Water trees in thoroughly when newly planted
2. Remove all fruit on trees planted in the last 2 years to reduce tree stress
3. Summer prune and train more frequently, winter pruning tends to promote vegetative vigour
4. Irrigate close to the tree, possibly invert micro-jets or adjust sprinklers to reduce surface wetting pattern. Consider conversion to drip.
For mature trees
Assess all blocks for financial performance. If blocks need to be prioritised, be sure you know which are more valuable for your business.
If a block is getting older or the variety is less competitive than it used to be, now may be a good time to renovate that part of the orchard to a new variety or style. Younger trees or regrafted trees will have lower water demand than 25 year old trees, to reduce canopy is to reduce water demand. Sometimes leaving a block vacant for an extra season is a good move if you are unsure what to plant.
Frosts are more likely in dry weather, though this was not seen in the dry spring of 2023. Keep interrow grass short if frequent frosts are likely. This will also reduce water demand of your ground cover to avoid competing with the orchard. If applying straw or mulch to improve moisture retention, be sure the risk of frost has passed.
Prune most valuable and productive blocks first, leave lower value blocks to last. This will give more time to evaluate rainfall in case a block needs to be reworked or removed.
Analyse your irrigation system for uniformity of coverage and to be as efficient as possible, upgrade old infrastructure if needed. At the start of flowering, monitor soil moisture to be sure winter rain has soaked the profile to 30cm depth. Monitor through the growing season, especially when rainfall stops in spring. If you don’t have soil moisture monitoring equipment, dig or auger a hole to inspect manually.
Deficit irrigation
The growth cycle has several critical periods for soil moisture, deficit irrigation can save up to 30% of water over a season —this applies to pears not apples.
1. Pre-flower, flower and fruit set.
From late August, soil moisture must allow root growth before flowers form. Avoid water stress up to 4 weeks after full bloom for fruitlet growth. Soil moisture monitoring may be required to calculate when irrigation starts.
2. 2–4 weeks after flowering, to 8 weeks before harvest. Potentially reduce irrigation by 60% of normal crop demand. Avoid over-irrigating during frost periods. Aggressive thinning may be required if water remains low.
3. Fruit growth, 8 weeks leading to harvest. During this period any moisture stress will reduce fruit size and the tree has its highest water requirement. Return to full crop demand. If water stress cannot be avoided, thin trees early after cutting back irrigation.
4. Post-harvest irrigation can be reduced by 60% but try to avoid leaf loss. Water in nitrogen fertiliser, maintain leaf activity but some wilting at midday is acceptable. Early maturing cultivars can see rapid shoot growth after harvest. Avoid water stress after harvest to ensure nutrients for budburst and shoot development in spring.
“ Limit irrigation when fruit growth is slow to avoid fuelling shoots that will later need to be pruned. ”
The APAL website has a handy guide on watering rates for drip and sprinklers at each growth phase, including intervals between watering:
The DPIRD website has an irrigation calculator as a starting point for making a yearly water budget.
Location, soil type and early or late stage fruit can be selected to indicate water demand from month to month.
Considering long term changes to your system?
Conversion from sprinkler to drip irrigation will significantly conserve water with a reduced wetting pattern. Be prepared, a tree that has been raised on sprinkler irrigation and changed to drip will stress initially when needing to search differently for water. Drip irrigation systems also enable the efficient supply of nutrients to the tree via fertigation to meet demand at the appropriate time.
Soil moisture monitoring will give an indication of when to start irrigation in spring. Vigorous rootstocks should be able to access stored winter moisture longer than dwarfing varieties. Drip irrigation will need to start earlier in the season than sprinkler due to a smaller root system.
For growers that are interested in precision irrigation management, researchers in the PIPS 4 Profit Soils project are trialling the SWAN Systems platform on Joe Fontanini’s Orchard. SWAN Systems (Scheduling Water and Nutrients) is a web-based irrigation and nutrient management program that includes water and nutrients planning tools, and live data collection from in-field devices to track weather, soil moisture, water use, and drainage.
SWAN uses live data to calculate daily soil moisture balance, and provides a soil moisture forecast to facilitate irrigation decision support for the week ahead. For nutrients, SWAN allows full nutrient program planning based on targets for each element and users can record actual nutrient applications for comparison and reporting against the budgets. Joe has implemented SWAN for 2 seasons and is willing to provide growers with an overview of the effectiveness of the program.
Acknowledgements:
• With contributions from Neil Lantzke, Kevin Lacey, Simon Yeap, Dr Nigel Swarts.
• AgVictoria — Australian Tree Crop, March 2024 issue
• APAL Future Orchards Library — “Irrigation Scheduling of Pears using Regulated Deficit Irrigation”, Ian Goodwin, 2009.