The most common irrigation system for vegetable production in the south west is semi-permanent overhead watering. Using drip irrigation can potentially lead to reduced water application without reducing yield. Drip irrigation may also decrease irrigation run-off and nutrient leaching, reducing erosion and nutrient losses into the environment.
The incidence of fungal diseases that can flourish in the moist environment created by overhead irrigation may be reduced by drip irrigation as the plant leaves are not wet. Drip irrigation can also reduce pumping costs due to lower running pressure. Ease of automation and the ability to schedule irrigation events with precision are further potential benefits.
Demonstrations of cauliflower crops watered using drip irrigation were conducted in Manjimup over two summers in 2012 and 2013. Both compared drip irrigation with overhead irrigation and were on karri loam soils at the Manjimup Horticultural Research Institute.
The drip irrigated plots received overhead irrigation for site preparation, including weed control, and on the day of transplanting, to reduce transplant stress and settle soil around transplants. After this time the drip irrigated plots only received drip irrigation.
Drip irrigation systems have potential for a range of vegetable brassica crops. A small area should be trialled before implementing a new irrigation system on a large scale.
Summary of results
In the 2012 crop, curd size and quality were similar between the drip irrigated and overhead irrigated plots. However, the drip irrigated plants tended to be greener, lusher and have more vegetative growth. They also matured slightly later.
The 2012 results were not repeated in 2013. The drip irrigated plots all produced lower yields with smaller curd size and lower quality. Plant size was also smaller. All drip-irrigated plots appeared to suffer from water stress.
It is unknown what caused the variability in results between the two seasons. However, there were longer and more extreme heatwave conditions early in the crop life in 2013. Sufficient water may not have been applied through the drip system to meet the needs of young plants with small root areas. Crop growth may have been set back from that time onwards.
If drip irrigation can produce equal quality and yield in the South West compared to overhead irrigation, then investment in drip irrigation may be worthwhile. Additionally, drip-irrigated plots used 25% less water when irrigated at the same rate as the overhead-irrigated plots. This was due to water only being applied to the root zone, not across the entire growing area.