Irrigation experiment

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Comparing fruit yield and quality with various irrigation strategies on Nectarine, using an Open Tatura trellis system.

Open Tatura Trellis irrigation experiment on Nectarine

Open Tatura trellis at the Stonefruit field laboratory, Tatura (Agriculture Victoria - DEDJTR)

Reduced irrigation inputs may result in higher fruit quality

The Irrigation experiment at Tatura's Stonefruit Field Laboratory aims to Identify the combinations of irrigation levels and timing that will enable the late season nectarine variety September Bright to achieve maximum uniformity in fruit quality attributes.

The experiment has three irrigation levels and four irrigation application timings as treatments.

The irrigation levels (% of tree evapotranspiration), applied using drip irrigation, are:

· 0: severe deficit irrigation to impose high level of water stress

· 20 & 40: deficit irrigation to impose a moderate level of water stress

· 100: control irrigation, crop water requirement to maximise yield

The experiment has four irrigation application timings and likely crop responses:

· Stage I of fruit development: water stress restricts cell division, reduces fruit size and yield

· Stage II of fruit development: water stress reduces vegetative vigour

·  Stage III of fruit development (early): water stress reduces fruit size and yield

·  Stage III of fruit development (late): water stress reduces fruit size and yield

Experiment 11

Video: Nectarine 'Open Tatura' tree training experiment using different irrigation strategies comparing fruit yield and quality.

Nectarine cv. September Bright
Planted winter 2014
Rootstock: Elberta
Treatments: Irrigation Level (ETc: 0, 20, 40, 100%) x Irrigation Timing (fruit growth stage: 1, 2, 3a, 3b)
Open Tatura tree training
2222 trees/ha

Video: Time series photos of Nectarine September Bright Open Tatura Irrigation Experiment

Results from the Irrigation Experiment

Dr Mark O'Connell discusses some of the findings from the irrigation experiment in the following video (9 min, 37 sec)

Transcript:

To target high quality fruit, strategic irrigation management practices, geared to specific fruit growth stages are currently being investigated in a design field experiment, at DEDJTR Tatura, at the Stone fruit field laboratory. The effect of water stress on stonefruit production varies with the severity of the water deficit and the duration and timing of that water stress. Typically fruit size is reduced under water deficits with the accumulation of soluble solids. The effect of other important fruit quality attributes like maturity firmness and skin colour are less well understood. So water stress during Stage 1 for example of fruit development is known to restrict cell division, reduce fruit size and decrease yield. Water stress during Stage 2 reduces the vegetative vigour with minimal impact on yield and fruit size. Consequently Stage 2 represents that traditional RDI regulated deficit irrigation period for reduced irrigation supply.

In Stage 2 of fruit growth, fruit growth rate is relatively low relative to the vegetative growth. Water stress however in stage three, reduces cell expansion of the fruit and is likely to restrict the remobilization of assimulate in the following seasons crop. Stage 3 water stress therefore impacts negatively on yield and fruit size. So at a Tatura the irrigation experiment aims to identify combinations of irrigation levels and timing of water deficits that will enable a late season nectarine variety of September Bright to achieve maximum uniformity in yield and fruit quality. The irrigation level's percentage of tree evaporation of the control being applied using the drip irrigation are, zero, 20 percent and 40 percent of the control. Zero treatment deficit irrigation treatment is imposed to give extreme high levels of water stress. The 20 percent deficit is to impose severe levels of water stress and a 40 percent deficit rirrigation treatment is to impose moderate levels of water stress. The control, 100 percent irrigation delivery of water is crop water requirement and in this stage to maximize yield and fruit size. There's different stages and timings of these water deficits, including stage one of fruit development, stage two of development and stage 3 of fruit development.

So when we observed this graph, we can see stage one, stage 2 and stage 3 of fruit growth. In stage 1, the period from September to early November, we can see the fruit growth rate in this curve here. In to stage 2, from November to January and Stage 3 is where the rapid fruit growth occurs,post January up until harvest in March. The relative growth of Shoots is also shown in the green line over those three periods, stage 1, stage 2 and stage 3 of fruit growth. So I've detailed here the 12 irrigation treatments we're using where we have different water deficits at different growth stages throughout the irrigation season.

The control, as mentioned, receives 100 per cent of water requirements all year across all fruit growth stages and post harvest stage four. As an example, in stage one we have zero percent irrigation. We have a 20 percent irrigation treatment and in stage one we also have a 40 percent irrigation treatment. In stage two, we have similar levels. Only in stage two the traditional RDI period has 0% treatment, 20 percent stage two treatment and a 40 percent stage two treatment.

In stage 3 of fruit growth, we have actually split stage three in half, that for a month between January and February, we call that three A and in the February - March window we call that a three B phase of fruit growth where we're also apply deficit irrigation treatments.

The results from last irrigation season, season 2016-17 season, we can see, we look at the year data, and we can compare each treatment, compared to the control, and typically we had no effect in Stage 2 with the green bars here, which is the traditional RDI period due to the deficit. They tend to yield no effect in Stage 3 A (let's call it the early phase of rapid growth). Major effect in yield production in Phase 3 B, and in the early phase 1 deficit irrigation treatment there appeared to be a couple of differences which we'll cover in a minute. So when we look at stage one. This is a histogram of the distribution of fruit weight compared to the control. So the black line here represents the control irrigated treatment, the well watered treatment compared to stage 1 deficits of 0 percent water, 20 percent water and 40 percent water on fruit size.

And what we can see as we have deficit irrigated in stage one we have a reduction in fruit overall fruit size, and a shift to the left in these distribution curves.  So we may compare the same data for fruit sweetness, the same treatments, we see a very similar response in overall fruit sweetness. However we did note that there was fruit size reduction.

Moving onto the stage 2 treatments, compared to the control, we have very similar profiles for fruit size and very similar profiles in fruit sweetness, suggesting that fruit size and yield was not impacted due to stage 2 deficit irrigation, which is the traditional RDI period, and fruit outcomes, fruit sweetness outcomes were quite similar as well to the control.

When we go to stage three, we can see major changes in reductions in our fruit size profiles compared to the control, and extreme changes in both fruit size for the late season, stage three, part two (let's call it the second phase, the last phase, the last month prior to harvest) where we deficit irrigated trees that were either 0 percent or 20 percent of water. We saw a huge shift to the left in smaller fruit compared to the control, and consequently we saw an increase in their fruit size reduced and a major change in the profiles of sweetness and those two deficit irrigated treatments just prior to harvest.

There was also, when you look at the early stage 3 deficit treatments, the 3.1 Zero %, the 3.1 twenty % and 3.1 forty % treatment , we also had fruit size reductions, but we didn't see any changes in their fruit sweeteners profiles.

The irrigation experiment has shown in the first season, that we need to well water our fruit trees in stage one of fruit growth to avoid that fruit size penalty. To maximize fruit size, we need to have well watered trees in phase one, and phase 2 (the RDI period), we saw no effect on fruit size or fruit sweetness, suggesting that there is potential for water savings using RDI in stage two of fruit growth. In stage 3, we found big differences in fruit size and fruit sweetness when we set deficit irrigation close to harvest, and so withholding water did increase fruit sweetness, but it also penalized fruit size. So further work needs to be done to refine that to optimize for equality in Phase 3 of fruit growth.

Continuous detection of plant water status in high density ‘September Bright’ nectarines

This study aims to test plant-based sensors for their efficiency in determining nectarine water status in a modern high-density orchard.

Alessio Scalisi from the University of Palermo (Italy) is working with Dr Mark O’Connell and Dr Dario Stefanelli at the Stonefruit Field Laboratory (Tatura) over the 2017/18 season.

Alessio Scalisi in the stonefruit orchard

Climate changes are leading to shortages of water worldwide, affecting traditional horticultural management strategies. Improved understanding of crop water requirements, coupled with irrigation automation play a key role for water saving in future fruit crop production. However, although automated, irrigation is often neither efficient nor timely in responding to seasonal changes in tree water need.

Fruit gauge on ‘September Bright’ nectarines

Measurements are underway on ‘September Bright’ nectarines grafted on Elberta rootstock, and trained to an open Tatura system (2222 tree/ha). Fruit gauges and leaf turgor pressure probes are mounted on trees subjected to four different irrigation levels: 100, 40, 20 and 0% of ETc at different fruit growth stages. Fruit relative growth rate (RGR) and leaf turgor pressure (Lp) dynamics are being studied and compared to midday stem water potential (╬Ęstem), the reference method for plant water status detection. Relationships between plant water status indexes (RGR, Lp and ╬Ęstem) and vegetative growth (trunk cross-sectional area, lateral strength and pruning weight), fruiting behaviour, fruit size, light interception and leaf gas exchange will be presented and discussed with respect to irrigation management.

Leaf turgor pressure probe

Irrigation Headworks Shed for Stonefruit Field Laboratory

Video: Irrigation headworks shed for field experiments.

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