Farm Table says:
What is the problem?
This report provides a summary of the methodology and outcomes of research into citrus survival of, and recovery from, drought and reduced irrigation availability. The scope of the work encompassed both a controlled research trial and a broad scale on-farm monitoring program.
The Murray Darling Basin (MDB) is the largest river basin in Australia. Water from its rivers has been used to irrigate a wide range of crops, including pastures for meat and milk production, cotton, rice, vegetables, vines and fruit trees.
Irrigation allocations are generally declared early in the financial year, which coincides with the water year.
However, the policy is to only allocate water that is available at the time of announcement of the allocations.
Allocations are then revised (generally upward) as storage conditions change during the season, for example as more inflow to the storages occurs.
What did the research involve?
In response to drought conditions and reduced water availability in the Murray Darling Basin, a research project was undertaken to investigate the impact and management of deficit irrigation in tree crops, including citrus and almonds.
This event was an ideal opportunity to collect valuable information for tree crop industries which will need to manage future drought events.
Citrus Drought Research Trial:
- the trial was conducted in a planting of approximately 1100 Valencia orange (Citrus sinensis (L.) Osbeck) trees budded onto Sweet Orange rootstock, located on a large irrigated property near Berri, South Australia (34°21’S, 140°36’E)
- three levels of irrigation were applied to the trees, based on meeting apparent crop evapotranspiration
- irrigation events were applied as full depth applications, and the timing was stretched between irrigations according to irrigation treatment
- irrigation treatments were determined against soil water monitoring data from a neighbouring planting
- this has implications for the interpretation of data, especially the differences between MDI 1Y and MDI 2Y treatments
- within each deficit irrigation treatment 3 different cultural management treatments were applied, along with a control treatment, to test the impact of different management on production maintenance (MDI) or tree survival (EDI
- nutrition treatments were not applied to the trial patch. Instead, the existing proportional fertigation protocol utilized across the property was continued
- a number of measurements were undertaken only during the first 2 seasons of the trial, whilst irrigation level treatments were in place
- content Soil water content was monitored weekly throughout the trial, using logging capacitance probes (Sentek® Diviner 2000®), at 10 cm intervals down to 160 cm depth
- canopy temperature (Tc) was measured weekly during the initial 2 seasons, using an infrared thermometer with a spectral response between 6.5 and 18 µm, and a 10:1 optical resolution
- fruit counts were conducted during the initial season (2008/09), in December 2008 (after initial fruit set, but before the second fruit drop) and March 2009 (after the second drop). Counts were taken within a cube-shaped quadrat 25 cm in each dimension, at 4 locations per tree (one each at the NW, NE, SW and SE corners)
- the plant physiology and crop response data collected according to the description above was subjected to Randomised Complete Block Analysis of Variance
On-Farm Drought Monitoring Program:
- individual plantings of consistent plant material and treatment were identified as distinct “sites” for the purpose of monitoring
- yield data were collected and analyzed, in order to assess the impact of the irrigation strategy on production
Data Collection and Manipulation:
- data on plantings and irrigation system at each site were collected and entered into IRES
- detail about the cultural treatments that were applied to each site, such as hedging, pruning, anti-transpirant sprays etc. was collected
- yield was the dependent variable, plotted against applied water (irrigation plus rainfall), crop evapotranspiration
- regression analysis on productivity was carried out in order to identify significant relationships between variables collected as part of the Drought Monitoring Program
What were the key findings?
Citrus Drought Research Trial:
- soil water content data over the course of the trial are shown in Figure 4, as monthly averages for irrigation treatment
- the pattern of soil water content measurements confirms that the irrigation and duration treatments created a greater deficit in year 1 than year 2; and the greatest deficit in EDI, a moderate deficit in MDI, and the least deficit in FI
- canopy temperature (Tc) averaged across 4 trees by 9 irrigation and cultural treatments, 2 durations and 3 replicates (n = 216), for 6 selected dates in early 2009.
•There is only one date amongst the displayed data when there is a significant difference between 2 of the EDI treatments (EDI GA warmer than EDI Hedge on 20/01/09).
Leaf Water Potential:
- predawn and midday leaf water potential (Ѱp and Ѱlm) for the 2008/09.
Leaf Area Index:
- during the same period, the full irrigation treatment trees suffered a gradual decline in LAI, to finish in a similar condition to the droughted trees
- by July 2010 there was no significant difference in LAI between any of the treatments
- at the March 2009 measurement, all treatments were still under a deficit, but the 1Y treatments returned to full irrigation soon after this (July 2009), however, LAI followed a similar path despite this change
- of particular interest was the consistent low fruit count across the EDI cultural treatments. The cultural treatments applied were designed to enhance the natural fruit drop, to minimise the stress experienced by trees from carrying too high crop load
- the general shape of the growth curve is similar for all seasons and all treatments, with rapid growth during spring and summer after final fruit set, slow growth through winter, and the second spurt of growth in the following spring
On-Farm Drought Monitoring Program:
- number of Monitoring Sites – At the beginning of the project, a number of property owners agreed to participate in this research, and a large number of sites (planting patches) were identified for ongoing monitoring
- a wide range of management strategies was used by citrus growers to nurse trees through reduced allocations. The strategies varied according to the degree of restriction of allocations, as well as the philosophy of the grower
- removal of the developing crop was another strategy, usually combined with hedging
- a fairly common strategy was the conversion of the irrigation system, in many cases to drip irrigation, but also to partial cover sprinkler systems
- conversion to drip irrigation was also accompanied in some cases by the establishment of Partial Rootzone Drying (PRD)
Yield Response Data:
- in all of the sites monitored for this project, this was the target variable, and all other varieties planted were used primarily as pollinators for Non-Pareil
- similar graphs were derived from pollinator varieties, but are not presented here
- the boundary line suggests maximum yield was achieved at around 1500 mm of applied water
One of the most useful tools at irrigators’ disposal during the drought was water trading across the Murray Darling Basin.
Given the mix of crop types along the river system, some irrigators were in a position to postpone growing their normal crops (pastures for dairy, rice and cotton), and instead traded water to irrigators with permanent plantings who did not have the option to cease irrigating for a season or two, and then recommence irrigating.
Related to water trade, it was important that traded water could be transferred between licences as rapidly as possible, to allow irrigators to access traded water quickly. Mechanisms were put in place by the relevant state authorities to facilitate this process.