Irrigation can be used as a tool to manage temperature extremes in vegetable crops. Temperature stress is likely to occur either as:

• High temperature spikes or heatwaves; or
• Frosts.

Heatwaves

Overhead solid-set irrigation or hand-shift sprinkler irrigation can reduce the temperature of foliage, flowers or fruit during high temperature extremes. It would be possible to use travelling irrigators or centre pivots for the same use.

Growers could consider retaining the capacity for using sprinklers for temperature mitigation. In lettuce production for example, it is common practice to install both trickle- and solid-set sprinkler irrigation on the same crop. The solid set is used to keep the soil uniformly moist for good crop establishment, especially on direct-seeded crops. The trickle irrigation is then switched on for the main growing cycle to maximise water use efficiency and availability to the plant.

Frost control

Frosts can cause severe damage to vegetable crops. If the predicted increases in the variability of the climate occur, especially in the frequency of extreme hot and cold spells, then frost is likely to become a more important issue than is currently the case.

The potential economic impact of frost is much higher than changes in average temperatures might seem to suggest. Average temperature changes will be gradual and there will be time to change species or varieties, or even move to new regions over time if required. However a severe frost can have a devastating effect on the profitability of a farming operation.

The extent of this potential loss depends on the length of the growing season. Short season (4-8 weeks) crops such as lettuce and other leafy salad vegetables are least likely to be affected. Longer-term crops such as brassicas, carrots, beetroot and sweet corn are more likely to be affected, although the most frost-sensitive stages are usually in the germination and establishment phases.

Vegetable growers are in a strong position in relation to managing frost because they can irrigate crops, especially with overhead sprinklers, which is a powerful tool in minimising frost damage.