Early results of the jointly-funded Agriculture Victoria and Victorian Endowment for Science, Knowledge and Innovation (VESKI) sustainable agriculture fellowship program indicate pear growers may be able to significantly save water without loss of yield.
Visiting Italian plant physiologist and inaugural VESKI fellow Professor Luca Corelli Grappadelli, from the Department of Agricultural Sciences, in Bologna, studied irrigation in pear orchards during his fellowship.
He put three watering regimes to the test in the pear orchards: the Agriculture Victoria recommended level (100 per cent), half that (50 per cent) and fifty per cent above the recommended level (150 per cent). The growth of individual ‘ANP-0534’ pears on the trees under the different irrigation regimes was then measured using specially-designed fruit gauges.
When irrigation rates were as low as half of what is recommended there was very little drop off in fruit growth for most of the season (during November and December). In January and February this changed, but the extent of increased supply of water needed by then is still being determined.
Under varying weather conditions encountered at the experimental site with large changes in temperature and relative humidity from one day to the next, fruit growth was altered more or less in real time.
On warmer days, fruit shrank considerably during the warmer part of the day, but recovered at night, so growth did not suffer from the warm weather. However, growth was maintained even during cooler, cloudier days, when less shrinkage/expansion occurred. Researchers will be looking to see if accounting for lower demand for days of cooler weather might lead to a potential to save irrigation water.
Luca said although any final conclusions would have to wait until post-harvest testing of fruit quality and storage performance was completed, the results would give growers a much clearer understanding of how fruit growth responded to weather conditions.
Fruit is now in storage and has been assessed for, and will again be assessed later for, dry matter content, soluble solids concentration (i.e. sweetness), flesh firmness, colour, chlorophyll breakdown and eating acceptability.
“Growers often don’t want to take the risk of applying less water,” said Luca. “This work will provide data that will give growers confidence to put on less water on days when it’s not needed by the fruit.
“It’s early days, but if the post-harvest study shows fruit responds in the way expected and less water leads to more soluble solids, at the very least it suggests growers could afford to cut back on irrigation and have better quality.”
Luca joined Agriculture Victoria researchers Bruce Tomkins, Ian Goodwin, John Lopresti, Susanna Turpin, Mark O’Connell, Dave Cornwall and Wendy Sessions.
Project leader Bruce Tomkins said the project enabled the development and testing of new and emerging sensor technologies in an effort to control pre- and post-harvest factors that affect fruit yield and quality, particularly on fruit composition.
This research was carried out within the four-hectare Pear Field Laboratory at Agriculture Victoria Tatura, a very efficient research orchard with a variety of experiments underway, to test the response of new red blush pear cultivars to a range of practices including irrigation, tree density, canopy management and rootstocks.
“It is anticipated the project will deliver more efficient pear productions systems and will enable growers to produce fruit that meets consumer expectations, thereby driving demand in domestic and Asian markets,” Bruce said.
Luca said that although simple, the pear irrigation experiment was the most technologically intensive project he had ever taken part in with thousands of data points collected daily.
“Recording rate of fruit growth and sap flow through the tree every 15 minutes for six months of the growing cycle is no small feat – and that does not include measurements of photosynthesis, average ‘traditional’ (e.g. by callipers) fruit and shoot growth, water potentials and quality attributes of fruit,” he said.
“All this work will enable researchers to build up a very detailed picture of how fruit yield and quality is impacted under various water and weather regimes.”
As well as mapping growth versus water availability, Tatura research scientist Dr Ian Goodwin provided data on water uptake (transpiration) by the experimental trees, which complements the data from fruit gauges in order to model how water uptake and fruit yields responded to weather conditions.
“We are trying to isolate the difference between growth on a hot day and on a cloudy day,” Luca said. “We look at water uptake and fruit gauge measurements and overlay environmental factors such as potential evapotranspiration (calculated from weather data) to see how much water the plant loses and how much it puts to growth.
“If shrinkage is not the driver of growth, it may mean we can use less water.”
Conversely, researchers will be able to tell whether mild, temporary (as in during certain hours of the day) water stresses may increase carbohydrate accumulation, thus improving quality.
Is there such a thing as too much light?
A high tech fluorometer/InfraRed Gas Analyzer was used to measure photosynthesis and chlorophyll fluorescence in pears in the orchard to assess how energy conversion in the chloroplast is affected by high light levels.
“In Italy, we cut water use in apples by 55 per cent after realising a lot of light may not be good (e.g. for leaf burn and photodamage to the leaves), therefore resorting to shading to make canopies more water- and energy-efficient,” Luca said.
“Under high light, leaves undergo damage not unlike the way we sunburn. They are adept at protecting themselves and can repair damage very rapidly, so fast we can’t see it in nature, but a lot of a good thing (light) may result in damage to the chlorophylls that ultimately causes reduced yields.
“We think that energy spent on repair and the decreased photosynthesis combines to reduce photosynthesis by up to 10 per cent a day. Is there a lot of wisdom exposing all the leaves to maximum light?
“By shading the trees, we can reduce the damage and at the same time reduce water use. If we could increase efficiency by 10 per cent we could make growers more sustainable, but there are no models for that, it needs to be tested and confirmed in new environments. Where better than in Australia.
“Growers train trees to intercept maximum light. The Tatura V trellis is already very efficient. There is 25 per cent more light here than I have ever seen anywhere else in the world due to less ozone, clearer skies and the fact the air is drier.
“The question is, when we are already intercepting high light should we go for more?”
Luca said it was too early to tell what the results of the photosynthesis experiments indicated.
“It may be that the photosynthesis rates are not so high,” he said. “That might make sense due to damage but it could be due to other factors.
“Yields are there. We need to see harvest data – if it comes in with high yields and low fruit size, maybe we should have thinned more. If yield and size have not decreased, photosynthesis may be down, but low vegetative vigour may mean that more carbon goes into fruit and production is safe.”
A team effort
Luca paid tribute to the high quality and design of the Tatura Pear Field Laboratory.
“It was an important component that this experimental orchard was available,” he said. “It is extremely well designed. If we didn’t have an orchard at this stage, I couldn’t have come out and done this experiment.”
He said technology had made it so much easier to measure and understand the mechanics of fruit growth and how it was coupled to environment and water.
“In the short term there are things we would like to do like correct the crop load,” he said. “A little down the line we would hope to be looking at fruit growth velocity in grams/minute measured at 15 minute intervals to understand how fast fruit is growing on a daily basis.
“If we can manage irrigation based on fruit performance we would bring a new paradigm to fruit growing, which is currently relying on measurement of allied parameters (i.e. soil moisture; stem water potentials) to deduce how well or poorly the tree is irrigated and consequently how the fruit should be growing.”
Profile: Luca Corelli-Grappadelli
Prof Luca Corelli-Grappadelli is a plant physiologist from the University of Bologna, in the north of Italy, who has spent the past three decades specialising in the ecophysiology of fruit trees, instrument/sensor design and development, and precision management of fruit crops.
From a family of fruit growers himself, he said he was keen to “give growers a better weapon to allow them to stay in the market”.
Having visited Tatura and sent several of his PhD students to work in research stations worldwide, he welcomed the opportunity to participate in the VESKI international fellowship program.
“Tatura is famous in the world,” he said. “I have known their work for a long time and there have been links between us for a long time.
“My personal interests are in the environmental conditions which are very similar to Italy and in the light conditions, which are more extreme than home. This may be a place where excessive light levels lead to extensive photo damage of the chloroplasts, causing reductions in photosynthesis. If true, there is the opportunity to test ideas in a new environment.”
He said one of the most interesting “unexpected” things he learned while at Tatura was the management of water issues in an advanced society.
“Water rights, water markets, diversions are all new to me. I thought the issues we face in the Emilia Romagna region where I live were complex already, but they do not come even close,” he said.
There is only one comparable irrigation project delivering water at 245 megaliter per hour, but growers can receive this water at very low costs.
Orchard operations tend to be much smaller in Italy than in Australia. Italian growers do almost everything by themselves or with the help of family members, and most belong to co-operative packing houses that sort, store, sell and ship the fruit.
The emphasis for Italian farmers is firmly on increasing efficiency. Yields per hectare are often lower than is reported as average in Victoria (e.g. 70 t/ha for Pink Lady®), but fruit size must be larger (at least 75 mm for Pink Lady and Golden Delicious, and 80 mm for Fuji and Modì™) to be saleable.
There is a different business model for farmers in Italy, as they have a smaller production potential (due to smaller acreage), therefore a very strong emphasis on increasing the efficiency of the whole operation. This creates interesting conditions for researchers as well.