Friday, December 1, 2023

Is this the future of irrigation?

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Curbing water consumption and the leaching of nitrogen is no easy feat but a major research programme has devised an ingenious plan. Luke Chivers explains.
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A six-year research programme on irrigation has ended with a big win for agriculture – the development of promising new sensor technology systems that give arable, vegetable and pastoral farmers the tools to use precision irrigation at sub-paddock scales. 

The systems work alongside existing irrigation scheduling technology, mapping and monitoring a field at sub-paddock scales and calculating exactly how much water is needed at the right time and place. It is a leading development for irrigation and field trials have proved to dramatically reduce water wastage, save users money and minimise farm runoff.

So, how did researchers do it?

New irrigation systems over the past two decades have let farmers and growers accurately apply water at appropriate intensity.

But the amount of water required on different soil types and pieces of land varies from place to place and without the correct application users found too little or too much water could easily be applied, causing yield losses. And too much irrigation results in run-off and nutrient leaching as well as wasted water. 

A Ministry of Business, Innovation and Employment-funded programme, dubbed Maximising the Value of Irrigation (MVI), led by Landcare Research with Plant and Food Research and the Foundation for Arable Research, took on the challenge.

Researchers did three field trials at Plant and Food’s experimental station at Lincoln. They showed water savings of 9% to 30% when irrigation was varied according to different crop water demands monitored in different soil management zones.

They used high-resolution sensor mapping and in-field soil and crop sensor monitoring systems.

“The sensor mapping used a vehicle mounted with GPS and an on-board data logger and towed an electromagnetic sensor that sensed the soil and collected information on the differences in soil moisture and texture,” MVI programme leader and Landcare scientist Dr Carolyn Hedley said.

This sensor mapping system was tried on six farms to measure drainage characteristics and how much water each soil zone could hold.

Meantime, the group designed, built and used a smartphone app to measure the soil moisture content in the management zones in almost real-time and provided users with the information to guide precise irrigation schedules.

The trials showed promising results that saved water and almost completely stopped irrigation-related nitrogen leaching losses.

They showed irrigation could have been reduced to the poorly drained soil zone by as much as 60mm, to avoid over-wetting and possibly also increase yield, Hedley said.

“This equates to an unnecessary water cost of approximately $720 per year, assuming $2/mm/ha/yr, and a conservative yield loss equivalent to approximately $2400, assuming a yield penalty of 2t/ha for the 6ha zone, so VRI could potentially save this farmer approximately $3000 a year at this site,” she said.

Another group of MVI researchers used remote sensing to create a technique for monitoring daily crop water use.

Plant and Food researcher Dr Hamish Brown said “To know exactly how much water to put on a field there’s two approaches you can take. You can measure the soil water content, which is generally what irrigation scheduling is based on; or you can measure how much the crop is taking out of the soil as a direct crop water extraction method. 

“If you add that up daily you can calculate how much water you need to put back on the land.”

Researchers originally tested the technique in a rain shelter for two barley crop varieties.

They then applied different irrigation to each crop.

“We found that we reduced the water use a little bit in the heavy soil but in the light soil there was a considerable reduction in water use with no yield reduction in the crop, which is promising,” Brown said.

Researchers found their method reduced drainage to near zero and concluded it can substantially reduce the environmental impact of irrigation.

Effective irrigation for crops such as wheat, corn, grass seed and potatoes has been a significant problem for farmers around the globe for centuries. 

It’s a delicate balance to get the correct amount of irrigation onto the land without dramatically reducing production, wasting water and causing unwanted run-off.

Developing technologies to measure accurate real-time soil moisture and crop water use is of immense value to farmers and growers making irrigation decisions, Landcare said.

Canterbury farmer Steven Bierema has relatively flat and even land but soil moisture sensing has given him another tool for improved irrigation scheduling.

“You always think ‘the soil is dry, run the irrigator over it and job done’ but actually, no, it’s not accurate enough,” Bierema said.

“With irrigation scheduling you can track that soil moisture content and make sure the soil moisture is adequate for plant growth. 

“We run five irrigators on the farm with three soil moisture probes. We want to increase that because it really does give us a better view of what crops use and what growth stages they are at,” he said.

The technology has also been tried on a Hawke’s Bay farm with a large area of land to irrigate but a very limited amount of water available.

Although that farm has a mixture of different soils farmer Hugh Ritchie still found the technology effective.

“Different crops and different soils in a paddock have different moisture requirements at different times so having the ability to apply the water more effectively and efficiently at those different places means you get more efficient use of the water. 

“You are optimising the crop performance with that water. Because you are not getting it too dry or too wet the crop potential is maximised,” Ritchie said.

Over time the new software control models almost took over the irrigator, prescribing what the model thought would be the best for the crop at the time given the current and past weather.

Irrigation use remains a hot topic. 

Long, variable, dry summer conditions coupled with increased demands mean irrigation is now essential for consistent and quality food production on the east coast. Since the late 1970s the area of farmland under irrigation has doubled every 12 years. The latest figure shows 747,000ha being irrigated in 2017 and it is expected to reach more than a million hectares by 2035.

Preserving water resources and enabling farmers to have access to the amount of water they need is an ongoing discussion between regional councils and farmers.

The two groups agree high-resolution, sensor-informed irrigation scheduling has the potential to help make informed decisions for precision irrigation at sub-paddock scales.

And FAR said adopting this research could be the answer.

“Irrigation is seen as a contentious issue and adoption of the outcomes of this research should alleviate public concerns over potential wastage of NZ’s natural resources and the risk of unintended environmental pollution,” FAR chief executive Alison Stewart said. 

And while the industry is aware of the potential benefits of smart irrigation scheduling the next challenge will be for farmers and growers to integrate it into their farm business in a cost-effective way.

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