Results 2015-16
Irrigation water applied to netted treatments was recorded at 1.7 Mega Litres (ML) per hectare (ha), while 2.0 ML/ha was applied outside the netted area. Rainfall from September to April was 378mm while evaporation for the same period was 1190mm.
Average fruit diameter measured was 71.9mm under the black net, 72.9mm under the white net and 72mm in the outside netted area.
While there was minor hail during the season, no hail damage, bird damage or significant sunburn was recorded in any of the treatments.
Discussion and comparison between seasons
The difference in rainfall of the three growing seasons September to April was only 28mm, 362mm, 390mm and 378mm for 2013/14, 2014/15 and 2015,16 seasons respectively, while evaporation was measured at 1258mm, 1231mm and 1190mm.
To remove the difference between evaporation and rainfall between seasons, water applied to each treatment was compared to net evaporation (Evaporation minus rainfall). A lower proportion of evaporation replacement indicates a lower application of water.
Between 2013-14 and 2015-16 seasons irrigation water applied to the site was reduced from 0.78 of net evaporation to 0.23 in the department managed outside net treatment and slightly less in the grower outside net area 0.64 to 0.23 (5.8 to 2.0ML/ha). Inside the netted area irrigation water applied was reduced from 0.63 of net evaporation to 0.21 (5.3 to 1.7 ML/ha).
Assuming all rainfall was effective within the growing period, the total water applied to the crop, irrigation plus rainfall was reduced from 9.42ML/ha to 5.78ML/ha, a reduction of 60% over the three year demonstration
Fruit diameter during the demonstration was relatively constant in the department managed treatments, but an increase was seen in the grower section over the three seasons (68mm to 72mm). Results indicate that the 15-16 season using drip irrigation led to better fruit size in all but the black net treatment, Figure 1.
Reduction in sod culture led to less mowing and maintenance in the orchard. While lower light and excess vigour in the first two seasons under the netted area required increased thinning and pruning during the season.In the 2015-16 season, increased pruning and earlier installation of Extenday reflective mat resulted in better colour development under the net than experienced in previous years. While pack-out data is not available, the Lysters have commented that using drip irrigation led to reduced vigour and will most likely result in the best harvest of the three-year demonstration under all treatments.
The 66% reduction in water applied from 2013-14 to 15-16 resulted from the introduced drip irrigation on the site. Water was only applied in a narrow strip along the tree rows, reducing sod culture and therefore water use on the site. It is estimated the wetted area was reduced from full coverage of four metres between rows to a wetted area of 80cm diameter. The reduced storage capacity for the plant to extra water required frequent irrigation as many as three times a day during the peak of summer.
Confidence to reduce irrigation was gained from employing evaporation based scheduling as a reference to crop water requirements and fine-tuning applications using soil moisture sensors. Data form the soil moisture sensors allowed decisions to be made such as when to start the season’s irrigation, reduce irrigation prior to rainfall and re-commence irrigation after rainfall, with the confidence that the crop had available soil moisture and was not stressed.
An example using soil moisture monitoring to guide irrigation was following 100mm of rainfall in January. Irrigation was reduced form 9.6L per tree per day to 0.9L per tree per day for three weeks following the downpour. Irrigation was only being applied to replace nutrients lost to leaching until soil moisture had returned to levels prior to the rain.
Summary
Using drip irrigation will significantly reduce irrigation requirements but requires a more rigorous method of scheduling and monitoring. Following evaporation and using soil moisture monitoring should be part of any irrigation practice and is especially important when implementing a new practice to a business.
Netting reduced water requirement by approximately 20% more than a non-netted orchard. Change in practices, including summer pruning, pest control and time of colour enhancing was required to achieve fruit colour and quality of fruit inside the net.
While there was little sunburn during the demonstration, netting did reduce the incidence of damage and resulted in lower fruit surface temperatures in extreme heat events. When bird damage occurred, there was none under netting compared with outside netting. Hail enough to damage fruit was not experienced at the demonstration site during the demonstration, but it is thought that small enough diameter netting would reduce the velocity and therefore the damage caused by large hail.
A special thanks to Mauri, Ann, Tim and Michelle Lyster for hosting the demonstration site over the last three seasons, along with the department and funding partners - Horticulture Innovation Australia, Department of Parks and Wildlife and the Australian Department of Agriculture, and the State Government Royalties for Regions. Without their support and assistance this work would not have been possible. Also thanks to staff at the deaprtment's Manjimup Horticultural Research Institute for assistance whenever it was required, this was much appreciated.