Farm advice: Managing irrigation

An extremely wet winter followed by a challenging summer calls for proper irrigation management to keep up with the changing weather

It’s been a challenging summer to date for farmers and growers across New Zealand. After an extremely wet winter, November and December turned into some of the driest on record for many areas. A number of regions had some good rainfall in early January, but anyone with irrigation will need to keep a close eye on conditions over the next few months to keep up with the changing weather.

Over summer, when we have both extremely dry and wet conditions, understanding your soil’s water holding properties and how much water crop needs is crucial to help you plan your approach to irrigating. After rain, it can be particularly difficult to know when to switch your irrigation equipment back on, but with some basic information, this becomes an easier decision.

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Different soil has varying water storage properties. The full point (the maximum amount of water soil can store) and also stress point (the irrigation trigger) are two key pieces of information you need to understand. If soil moisture falls below the stress point, then the crop begins to suffer and productivity drops off. The stress point varies by crop. Some crops, such as pasture, can handle a few days of insufficient soil moisture with relatively little impact. Other crops, such as fruit and vegetables, can be quite severely impacted, particularly during early fruit development or ripening.

Knowing your full point is important, as this is the soil’s maximum water holding capacity, which dictates the maximum amount of water you should apply. If you apply water in excess of the full point, it either drains through the profile or runs off, often taking nutrients with it. Water applied above the full point is inefficient, as it’s not used for crop or pasture growth.

There are a number of consultants who can accurately work out your soil’s water storage properties as well as some good soil moisture monitoring tools. There are also daily irrigation weather forecast services you can subscribe to. These are all worthwhile investments. An irrigation strategy should aim to ensure that soil moisture is always sitting between the stress and full point. When temperatures change quite dramatically over a few days, soil moisture monitoring and weather forecasting can help you to know when water is needed.

It seems obvious but after heavy rain, it’s time to switch the irrigator off. The length of time you switch it off for will depend on how much water your soil holds and the weather. On my recent travels in Canterbury and Hawke’s Bay, I have seen a number of irrigators running both hours before and a couple of days after a downpour of rain. These farms don’t seem to be using soil moisture monitoring or weather forecasts. Unnecessary irrigation costs you money and also makes the public passing by question whether all irrigators are using water efficiently. If you switch off your irrigator after heavy rain, well done.

Irrigation training course

IrrigationNZ is running a range of irrigation training courses in February and March in Northland and Canterbury covering topics such as soil moisture monitoring, irrigation scheduling, irrigator performance assessment, and regulations.

To find out more, visit irrigationnz.co.nz/events.

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