It is generally accepted that dripline irrigation has some attractive attributes compared to sprinkler irrigation. These include less evaporative losses which leads to greater water savings, less ongoing maintenance, and lower system flows which mean lower power costs. Evaporative losses of 30% are common in under-tree sprinkler systems, whereas such losses from surface driplines are only about 5%. In practice this means that to replace 4 mm of daily soil moisture loss, a sprinkler system would need to apply 6 mm of irrigation. Over an annual period, the extra irrigation applied to overcome the 30% evaporative losses during application type are significant. If a grower was applying 6 megalitres per hectare annually via sprinkler it could be assumed that as much as 2 megalitres per hectare would be lost before it ever entered the soil.
Sprinklers do have some attributes that many growers desire. Sprinklers can wet up a greater soil area compared to a single dripline and sprinklers are better at wetting surface organic matter.
Double dripline row with nuts ready to harvest
South African macadamia growers have been evolving dripline irrigation on mature macadamia trees for a number of years (see Winter 2019 News Bulletin story). They have developed a system that uses two driplines per tree row. This wets up a wider strip than a single dripline system, and it gets close to the wetted area provided by sprinklers. This is a highly productive system that has many of the benefits of both drip and sprinkler irrigation. A key difference in South Africa is that they harvest their macadamia nuts by hand - they do not use machine harvesters.
Here in Australia the macadamia industry has always believed that machine harvesting of macadamia nuts off the ground inhibited the use of multiple on-ground driplines. It was thought that the finger wheels and the blowers or sweepers used on the harvesters would foul and damage the dripline. This had always been assumed, and had never been tested.
During the recent 2019 harvest, we thoroughly investigated if multiple on-ground driplines were compatible with current machine harvesting machinery. We asked the harvester operators to continue with their harvesting practices as normal, that is, full blower and typical harvester speed and positioning.
Test Site number #1
Driplines: 1 line of Netafim’s Uniram 16012. (16mm diameter, integrated emitters, 1.2mm wall thickness)
Position: Dripline approx. 0.8m out from trunks.
Pegs: Simple metal tent pegs every 15m
Machinery: Steinhardts harvester travelling at 7Km/hr. Blue front finger wheels and Yellow/ blue rear finger wheels and a blower.
Test Site number #2
Driplines: 2 lines of Netafim’s Uniram 20012. (20mm diameter, integrated emitters, 1.2mm wall thickness)
Position: Driplines 0.6m and 0.8m either side out from trunks.
Pegs: Netafim’s 5” plastic hold down stakes every 25m.
Machinery: MacMaster harvester travelling at 6Km/hr. Blower plus front and back finger wheels (yellow and Blue).
The dripline remained in place during machine harvesting.
Both tests were resounding successes.
We would recommend using plastic pegs rather than metal pegs to hold down the dripline as plastic pegs pose less risk to tyres and other farm machinery if they were lifted.
This result was a lightbulb moment for me as it demonstrated that machine harvesters can be used with multiple on-ground driplines in macadamia orchards. Australian macadamia farmers can now also explore the benefits of having multiple driplines that wet up a wide strip.