Irrigation New Zealand

IrrigationNZ says a new study by Aqualinc and the Fertiliser Association of New Zealand on how irrigation can be adapted to reduce nitrogen losses could help farmers and growers significantly reduce their environmental impacts.

The study showed that on 12 Canterbury dairy farms, an average of a 26% reduction in nitrogen losses could be achieved through changing when irrigation was applied on the farms.

“Farmers and growers who use irrigation want to see improvements to our waterways and environment and are working to achieve this. Most irrigators now have challenging targets in their Farm Environment Plans to reduce their nitrogen losses. The study has helped clarify when the most gains can be made in reducing nitrogen losses through irrigation management,“ says Andrew Curtis, Chief Executive of IrrigationNZ.

“The message for farmers from the study is that how you manage your irrigation in early spring and autumn has a big impact on your overall nitrogen losses. In wetter, cooler conditions there is more risk of nitrogen leaching through soils as pasture growth is slower so you need to adjust your irrigation as result of this,” says Mr Curtis.

“Based on the study results, farmers should look at not irrigating in September or April, as the nutrient losses may outweigh the benefits of some additional pasture growth. In October and March, we would recommend not irrigating as often as in the height of summer and allowing soil moisture levels to drop to around 40% - lower than the 50% level recommended in summer. This approach would work in most years, unless very dry conditions occur,” Mr Curtis says.

“Given that significant reductions in nitrogen losses can be made through irrigation management, we would like to see further research undertaken on how to adjust irrigation for different annual climate conditions. Overseer modelling simulates conditions in an average year, but we know that variations in rainfall and temperature affect growing conditions and irrigation use every year.”

IrrigationNZ is the national membership organisation for farmers and growers using irrigation. It carries out training courses and already recommends that irrigators adjust their irrigation in the spring and autumn to apply water less often to reduce nutrient losses.

Mr Curtis says that the study provides supporting evidence on the value of altering irrigation patterns in the shoulder season and the reduction in nutrient losses that this can achieve.

“Careful management of irrigation systems can make a big difference to a farm’s environmental footprint. There are a lot of things to be considered – understanding irrigation system capability and requirements, crop and pasture requirements, long-term and short-term weather forecasts, soil moisture monitoring and how to appropriately schedule irrigation,” Mr Curtis says.

IrrigationNZ covers different aspects of irrigation management in training courses – with the next two training opportunities scheduled for September in Ashburton and Lincoln – see

The Aqualinc and Fertiliser Association of New Zealand study, Reducing Nutrient Losses through Improving Irrigation Efficiency is available online.