Crop growth and yield
Crop health and growth was observed throughout crop life. Curd weight, quality and date of harvest were recorded for each plot at harvest. The results varied between 2012 and 2013.
2012 demonstration
During crop growth there was minimal signs of heat and water stress. A major concern before planting was the drip irrigated plots would not be able to withstand hot days without the cooling effect overhead irrigation provides.
About one week after transplanting there were several days of 35oC+ temperatures, and on the first hot day all plants in the drip-irrigated plots wilted severely. There was minimal wilting in the overhead-irrigated plots. All plants recovered well and were not visually affected by subsequent hot days and heatwaves.
There was minimal disease in all plots so no comparisons could be made.
Average curd weights were similar across all treatments, averaging between 990g and 1050g for marketable curds.
Overhead irrigation plots tended to mature earlier and peak harvest took place three to four days earlier than drip irrigated plots. The drip irrigated plants tended to be greener, lusher and had more vegetative growth than overhead irrigated plants. This could be due to luxury amounts of water and nutrients available to the plants. Larger plants did not lead to larger curds in the drip plots. In such a situation savings may be made in water and/or nutrient application without reducing yield.
Cauliflower roots were very good at accessing water and had different patterns of growth depending on the irrigation they were receiving. In plots with only one drip line the roots grew preferentially towards the centre of the beds, that is towards the drip line. It is not known if all varieties would be as effective at accessing water as the variety Boris.
2013 demonstration
Early in crop growth there were no visible differences between any of the drip-irrigated plots and the overhead-irrigated plots. Heatwave conditions were experienced about 10 days after transplanting and persisted for five days. At the time of the heatwave there was no wilting or other signs of heat or water stress in any of the plots. After the heatwave, the drip irrigated plots lagged in vegetative growth and were not as vigorous as the overhead-irrigated plots.
As the crop grew the drip-irrigated treatments progressively showed stress. The drip-irrigated plots started showing signs of water stress which corresponded with measured reductions in soil moisture. Plants were obviously smaller, with fewer and smaller leaves. The leaves were blue-grey compared to the green of the overhead-irrigated plots.
The plots receiving 100% evaporation replacement and variable drip irrigation rates produced larger plants than the 50% and 80% drip-irrigated plots. These plots also showed signs of stress two months after transplanting when compared with the overhead irrigated plots.
Smaller plants led to significantly smaller curds and lower yields for the drip-irrigated plots compared with the overhead-irrigated plot. More curds from drip-irrigated plots were also deemed unmarketable due to yellowing from exposure to sunlight. With fewer and smaller leaves, the drip-irrigated plants did not have sufficient vegetative growth to cover curds.
There was greater incidence of white blister infection in the overhead irrigated plots. White blister is spread by water and infection is more likely when leaves are wet. White blister did not impact on yield or quality in this cauliflower crop. It is a concern in broccoli crops where it can infect the head, reducing marketability.
There was more pest damage, particularly from diamondback moth (DBM), in the drip-irrigated plots. DBM will often target stressed plants first. The water stress may have made them more susceptible to insect attack, contributing further to reduced yield and quality.
Conclusion
These preliminary demonstrations have shown that drip irrigation of cauliflowers on karri loam soils in south-west Western Australia is possible.
The variable results between the two years highlights the need for further research into suitable irrigation system configurations and scheduling techniques that can reliably produce an economically viable crop across a variety of seasons.
Before undertaking any irrigation system changes, it is recommended that you consult with a certified irrigation designer.