Based on their on-farm experience and observations, lots of farmers believe irrigation can boost soil carbon and soil water holding capacity.

Former South Canterbury Federated Farmers president Ivon Hurst is chairman of a research project that over the next three years will look to nail those understandings down with hard science and peer-reviewed data.

"Anecdotal evidence is not enough," Ivon says. "It has to be scientifically validated and that's the way forward for all future land management practices."

Project research will be led by Landcare Research's Dr Sam Carrick, and a range of extension activities led by Katherine McCusker, of the AgriBusiness Group. It will support improvements in the management of soils to reduce environmental impacts and enable more accurate estimation of nutrient loss.

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"With nutrient discharge and water quality rules, the most glaring thing about it is that we are dealing with imperfect or unscientific assumptions all the time."

Through field measurements and samples involving 48 farms in Canterbury the project will quantify whether, under medium to long-term irrigation, soil water holding capacity increases compared with the same soil, in the same farm system, but under dryland conditions.

Effects of soil type and the number of years soil has been irrigated will also be studied.
Better knowledge around irrigation scheduling and modelling of nutrient leaching is crucial not just for Canterbury but irrigated areas around the rest of New Zealand, Ivon says.

MPI, the guardians of the Sustainable Farming Fund purse strings, agree. Earlier this year they granted the research project just under $300,000, which will be backed by contributions in cash and kind from Federated Farmers, Environment Canterbury, Beef + Lamb, Irrigation NZ, Dairy NZ, Landcare Research, irrigation companies and others.

Ivon says initial conversations about the project stretch back several years, including Ian Mackenzie (former Federated Farmers National Board member), Dr Lionel Hume (Federated Farmers senior policy adviser) and Trevor Webb, a leading scientist with Landcare Research. There appeared to be a knowledge gap on the relationship between soil water holding capacity and length of time under irrigation.

During this time, Trevor became involved in soil studies on Omarama Station, owned by 2015 Canterbury Ballance Farm Award winners Richard and Annabelle Subtil, who wanted to find out more about nutrient discharge on their land.

"Their alluvial flats had been under irrigation for 30 or 40 years, mostly with border dyke but more recently under centre pivot. The general assumption from Overseer was that those soils would leak nutrients like a sieve, but Richard wanted to know for sure," Ivon says.

Results from samples taken at Omarama were "significantly different from what was expected". They showed an increase in water holding capacity of 47 per cent in the top 15cm of soil. That piqued the interest of others, including Feds policy advisers Lionel Hume and Kevin Geddes, and former South Canterbury Arable chairman Colin Hurst.

The upshot was that, with a deadline for applications to the Sustainable Farming Fund looming, they put together a proposal for research trials on 15-20 Mid-Canterbury properties to see if the positive results from Omarama and other sampling in the Upper Waitaki Basin could be confirmed on a wider scale.

Through no fault of its proponents, it was turned down, Ivon says. "You can't rush a project through the SFF; it's government money and every 'i' has to be dotted and 't' crossed.

"They want to know it's going to have an outstanding effect, and the information is actually going to be used where it's aimed - in our case the farming community."

The idea might well have died right there. Those original proponents were soon busy with other tasks. But it just happened Ivon had to make regular trips south to deal with Plan Change issues around the Waitaki River.

"You talk about a lot of subjects when there are three or four farmers in a car, and it's one hour there and one hour back."

In short, they resolved that a more comprehensive irrigation/soil project brief deserved to be put to the SFF. Ivon remembers saying "this sounds far too good to let go". Following development of the project and a substantial rewrite of the application by Lionel Hume, Sam Carrick and Katherine McCusker, Ivon found himself project chairman, with Sam as project manager.

The first task, already under way, is to gather what written material and data is already available for categorising and entering on a computer database.

A recent Lincoln University masters graduate, Veronica Penny, has been contracted at Landcare Research to work on the project. One of Veronica's first tasks will be to support Katherine's extension side of the project by going through every scrap of paper in Landcare offices which make any reference to irrigation.

Papers from past research stations such as Winchmore, and scientific journals will also be trawled through.

"There's a huge amount of good stuff that has never seen the light of day since written," says Katherine. She is really keen to "dust it off and get the knowledge into the hands of our innovative farmers and irrigation industry specialists".

The resulting resource will be freely available to others, including irrigation companies, for future reference - "an added plus of the project", Ivon says.

Thanks to Federated Farmers' membership database, The Agribusiness group and their network of contacts, and Landcare Research's use of GIS mapping, the project team has plenty of names of farmers to approach for the sampling phase.

Some 48 farms with irrigated land, and control (non-irrigated) land of the same soil type and land use, are needed.

Ivon says when the project is wound up in June 2020, it will probably give rise to a series of other questions and research topics - including on nutrient leaching and nitrous oxide emissions.

This project is essentially confined to water holding capacity - the quantity of water available to plants that is held between field capacity and permanent wilting point.

"It gives you an indication of whatever else is sitting in the soil and once you start complicating things you can get pulled in too many directions at once. This is research that should have been done 30 years ago to be honest," Ivon says.

"What I suspect - it's only a personal view but I know others are thinking about it - is that this could start a series of collaborative exercises that Federated Farmers and Landcare Research can do over a number of years, in terms of establishing effects of water on soil, and other farming practices on soils.

"With nutrient discharge and water quality rules and so on, the most glaring thing about it is that we are dealing with imperfect or unscientific assumptions all the time. We do not have enough hard science to come out and be able to say 'x' will lead to 'y'."

There are good reasons for doing the initial research in Canterbury, home to about 80 per cent of New Zealand's irrigation. "It's the cutting edge of irrigation so we might as well start where it's being utilised in the greatest amounts."

Ivon believes it's likely that at the end of the three-year project, "the same thing will need to be replicated in other areas, particularly the east coast of both islands".