The basics of irrigation during hot weather

Hot, dry conditions test even the best irrigation strategies.

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When temperatures climb and the wind picks up, even well-managed fields, vineyards and orchards can start showing signs of stress.

The instinct is often to “just add more water”, but during hot spells it’s less about volume and more about timing and technique, says Christo van der Westhuizen, agronomist at Netafim Southern and East Africa.

Different crops reach heat-stress thresholds at different temperatures, but all become more vulnerable when soil moisture drops, making well-timed irrigation essential. He explains that soil, depending on its type, depth and texture, has a limited water-holding capacity, almost like a glass. Once that ‘glass’ is full, any extra water simply runs off or drains too deeply to be useful.

Worse still, over-irrigating can saturate the soil pores that normally hold air. Roots need that oxygen to function properly, so waterlogged conditions can slow root respiration, reduce nutrient uptake, and leave plants more prone to stress and disease.

“The tricky part is that the symptoms of this type of damage are almost exactly the same as when plants don’t receive enough water,” he says.

HAVE A PLAN

For Van der Westhuizen, the best way to deal with hot weather and heatwaves is to have a detailed irrigation plan for each block that considers the crop being produced, its age, and stage of development, expected crop load, and soil characteristics such as texture and water-holding capacity.

The plan should then be adjusted weekly based on weather forecasts to account for environmental conditions that can influence evaporation and soil moisture levels, such as high temperatures, wind and any expected rainfall.

Simultaneously, soil moisture levels should be continuously monitored to confirm how much of the applied water ends up in the root zone of the crop.