Farms across Heretaunga Plains investigate impact of tile drains on water quality

Leander Archer, Horticulture and Environment Consultant at AgFirst Consultants wants to know all about the impact of tile drains on waterways. Photo / Supplied

Hawke's Bay farmers are raising their hand to trial tile drains as part of a new project looking at the impact of them on water quality.

Six pipfruit orchards, four kiwifruit orchards and four cropping farms spread through the Heretaunga Plains area will tile drains as part of a $1.34m MPI-funded project set to begin in spring.

But what are tile drains?

Leander Archer, horticulture and environment consultant at AgFirst Consultants, who is leading the project, said tile drains were used to divert excess moisture from the soil.

"They are regularly spaced (e.g. 20m to 80m spacing) pipes dug down into the soil, often at 1m depth that speed up removal of excess water," Archer said.

"They used to be made of clay sections of pipe lined up against each other, and now often use plastic piping.

"These drains increase crop health both in winter (more oxygen to roots) and in summer (more roots survive wetter season, increasing drought resilience)."

Archer said they hoped the project would enabled them to "better understand the impact of tile drains on water quality so that, if needed, growers could implement the required management strategies to improve nutrient efficiency".

"This will benefit not only the environment, but also orchard productivity by addressing the loss of valuable soil or nutrients that are essential for crop growth."

To select a site AgFirst talked to more than 40 grower companies in the Heretaunga Plains area.

"The Heretaunga Plains has been selected because it has extensive tile drainage networks and a range of groundwater pressures and soil types, and much of the catchment is used for high-value horticulture. Plus, the Karamū catchment within this area has reported water quality issues," Archer said.

"Horticulturalists want to grow healthy food that contributes to healthy communities, in a way that cares for the soil and waterways that sustain us all. This research will help them to do that. If you don't measure it, you can't manage it."

She said AgFirst had positive response from growers wanting to find out what their water quality looked like.

"Many sites were not usable for the project because the tiles were installed a long time ago, so we did not have a good map of where they were.

"Of those that did, many did not have two tile exit points that could be paired for measurement.

"Paired sites mean we have two exits out of the same block we can measure in year 1 and 2, and if needed, trial a change in management practices over one tile and not the other in year 3."

The Ministry for Primary Industries (MPI) is contributing $1.34 million towards the project through its Sustainable Food and Fibre Futures (SFF Futures) fund.

Steve Penno, MPI's director of investment programmes, said the outcomes of the research had the potential to provide deeper insights into how the horticultural industry could become more sustainable.

"We all want clean waterways," Penno said.

"At the very least we'll gain more information about whether this is a problem we need to address. And at the most we'll identify the size of the issue and how to best measure nutrient losses to understand how to mitigate these."

AgFirst Consultants is finishing the site selection process for the trial farms, for monitoring to begin in spring.