The effect of medium- to long-term irrigation on soil water holding properties

What is the response of soil physical properties to irrigation?

Farmers are becoming increasingly interested in how soils change under irrigation, as a result of their on-farm observations and experiences. Former South Canterbury Federated Farmers President, Ivon Hurst, is chairman of a MPI Sustainable Farming Fund research project that will examine those understandings over the next 3 years through scientific measurements 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.”

The project is led by Federated Farmers and backed by contributions in cash and kind from Environment Canterbury, Beef + Lamb, Irrigation NZ, Dairy NZ, Manaaki Whenua – Landcare Research, and seven Canterbury irrigation companies. Manaaki Whenua’s Sam Carrick will lead the project research, and a range of extension activities will be led by Katherine McCusker, of The AgriBusiness Group, supported by Lionel Hume from Federated Farmers. A recent Lincoln University Masters graduate, Veronica Penny, has been contracted at Manaaki Whenua to work on the project.

This project involves working with farmers, rural professionals, scientists, and regulators to:

• access previous research knowledge and findings on the response of soil physical properties to irrigation
• fill an important knowledge gap, through field measurements, to quantify whether, under medium- to long-term irrigation, soil water holding capacity increases compared with the same soil and farm system under dryland conditions
• upskill them on the knowledge and understanding of how soils respond to irrigation, and which practices will potentially have the greatest positive impact on the ability to efficiently manage water and nutrients.

The first task, already underway, is to gather what written material and data are already available, by searching previously published research in a range of sources from scientific journals to reports from past research stations such as Winchmore, Templeton, and Timaru. “There’s a huge amount of good stuff that has never seen the light of day since it was written”, says Katherine, and she is really keen to “dust off the shelf and get the knowledge into the hands of our innovative farmers and irrigation industry specialists”.

The second stage of the project, also underway, will involve field sampling across 48 farms in Canterbury to 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. Through the use of Manaaki Whenua’s GIS mapping skills, the project has identified a range of potential pasture paddocks across Canterbury that may contain both irrigated and dryland areas (Fig. 1). Thanks to Federated Farmers’ membership database, The Agribusiness Group and their network of contacts, and the local knowledge of the participating irrigation companies, the project team is currently refining this list against suitability criteria, with the field work due to start in August 2017. The project will also look at the effect of soil type and length of time under irrigation, to determine their roles in how soil water holding properties may change under irrigation.

A strength of the project is the collaboration involved, shown by the large number of co-funding industry groups and the active cooperation with other funded science projects. The field sampling research works directly with both the MBIE funded S-map NextGen and MPI funded Impact of Irrigation on Soil Carbon Stocks projects – both of which are described in Our Projects. For the extension side of this project, we are working closely with the IrrigationNZ project “SMART Tools and Tips for Irrigators”, also funded by the MPI Sustainable Farming Fund, as well as with the extension programmes of our other co-funding partners.

The third major component of this project is to have a regular presence in industry magazines, farmer field days, etc. over the next three years, highlighting not just our research findings, but the knowledge generated in other science projects that may not have the degree of connectivity to a range of end-users that Federated Farmers has linked together in this Sustainable Farming Fund project.