Dr Mark O'Connell from Agriculture Victoria discusses RDI for stonefruit

Introduction

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: extreme deficit irrigation to impose high level of water stress
  • 20 & 40: deficit irrigation to impose severe and 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: cell division (rapid fruit growth) - water stress restricts cell division, reduces fruit size and yield
  • Stage II of fruit development: pit hardening (slow fruit growth, maximum vegetative growth) - water stress reduces vegetative vigour
  • Stage IIIa of fruit development (early): cell expansion - water stress reduces fruit size and yield
  • Stage IIIb of fruit development (late): cell expansion (sugar accumulation, chlorophyll degradation) - water stress reduces fruit size and yield

Table 1: Irrigation experimental treatments

2016-2017 Irrigation Experiment table 2016/17 irrigation experiment

Regulated deficit irrigation (RDI) occurs during stage 2 of development. See Graph below.

Shoot and fruit growth graph

Video: Introduction to the Nectarine irrigation experiments. 2015

Dr Mark O'Connell introduces the Nectarine, Open Tatura trellis, irrigation experiments.
  • Nectarine cv. September Bright with Rootstock: Elberta
  • Planted winter 2014 in Open Tatura tree training at a density of 2222 trees/ha

Results

2020

Sensing fruit and tree performance under deficit irrigation in ‘September Bright’ nectarine

This study aims to determine yield and fruit quality responses under deficit irrigation of nectarine in a modern high-density orchard.

Effect of drought stress and recovery on stonefruit production varies with severity, duration and timing of water deficit.

  • Typically, fruit size was reduced under water deficit. Water deficit also lowered yield, decreased canopy size (light interception), lowered stomatal conductance, reduced leaf chlorophyll, increased photo-inhibition, increased fruit soluble solids, increased firmness, decreased maturity and increased red skin colour coverage.
  • However, moderate water deficit (40% ETc) during the traditional RDI period (Stage II of fruit growth) showed no effect on yield or fruit quality.

Fruit & tree performance under deficit irrigation

2018

Plant Water Status Trial

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

Continuous detection of plant water status

2017

Video: Dr Mark O'Connell discusses some of the findings from the irrigation experiment in the following video (9 min, 37 sec). 2017
  • 'To maximize fruit size, we need to have well watered trees in phase one'
  • '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'
Results from the Irrigation Experiment

Virtual Orchard Tour - A look at tree structures in the irrigation experiments

September 2019 - Flowering of Nectarine September Bright

More Virtual tours more 360 degree photo tours of irrigation trees in the stonefruit research orchard.

Time series videos

Every few weeks photos were taken of each experiment, and produced into a video to show the resulting growth of tree canopies and fruit development.

Video: Photos of Nectarine, September Bright, on Open Tatura trellis, from 2015 to 2020

Video: Irrigation experiment -Time series photos of Nectarine September Bright on Open Tatura trellis 2015-2020

Project Acknowledgement

This research (SF12003 Increased stone fruit profitability by consistently meeting market expectations; SF17006 Summerfruit Orchard Phase 2) was funded by Agriculture Victoria with co-investment from Horticulture Innovation Australia Limited using the Summerfruit levy and funds from the Australian Government.