Project Updates

September 2025

Year 2 Trial Results Summary - The 2024-25 season trial results reinforce the relationship between soil moisture levels and soil compaction risk. Grazing soils at or near field capacity reduces macro-porosity and total porosity while increasing bulk density. However, no clear trend was observed between different ‘wait-time’ treatments. This is likely due to the wet summer and that both soil samplings occurred during periods of low evapotranspiration when soils were near field capacity, resulting in little variation in soil moisture between the four treatments. However, it could be that the initial grazing, which occurred when the soils were at field capacity, may have impacted the soils for the season. Also, field observations suggest that grazing ‘wait-times’ will vary seasonally and are likely influenced by evapotranspiration rates. For the 2025-26 trials, the design has been adjusted to ensure a broader range of soil moisture levels is sampled and to test the seasonality hypothesis.

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Year 3 Trials- The project will monitor three grazing wait times (24, 48, and 72 hours) for the 2025-26 season. This involves allowing 24 hours for soil drainage after irrigation before grazing on one plot, with the other plots allocated 48 and 72 hours, respectively. Soil measurements will be conducted in late spring/ early summer and late summer/ early autumn. This trial adaptation aims to improve the understanding of how soil water content, grazing timing, and soil compaction risk are related. The findings will also enable the development of grazing wait time recommendations for farmers across the season.

Practical Solutions - It is likely that grazing immediately after irrigation in spring presents the highest risk of soil compaction. To address this, the practical solutions component will conduct interviews with farmers and service providers to identify effective spring irrigation management strategies. Since low evapotranspiration rates and dependable water supply reduce the risk of falling behind schedule, there is greater flexibility in implementing various management options at this time of the season.

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​May 2025

The projects focus has been running the 4 field trial sites and associated treatments. Specifically this has involved liaison with each farm to ensure each irrigation treatment was applied at the required timing prior to grazing. The 2024-25 season was at times very challenging. Frequent rainfall events early in the season and again post Xmas meant soil moisture levels and grazing schedules had to be closely monitored to avoid adversely impacting the trial sites. Several grazing’s had be moved so they avoided directly coinciding with >10mm rainfall events, however, with the exception of one round, grazing's were able to be rescheduled so the rainfall event provided the irrigation treatment.

Each of the trial farms adopts a cover based rotational grazing system (as opposed to calendar based). This resulted in the need for frequent communication with the farm manager and/or grazing manager and/or irrigation manager, to ensure the irrigation treatments are correctly timed. It also highlights the complexities that will need to be worked through for the trial outputs to be successfully adopted into day-to-day grazing management and/ or irrigation practice.

Project communication has been limited noting the focus for this period has been running the trials, however Primary Insight has held 3 irrigation workshops where the project and its objectives were discussed. One of these was with Lincoln University Farm staff, another with the Camden Group farm staff and the last a general session held at Dunsandel. As before farmers commented that they use to 'hold-off' grazing in the past when irrigating with Southern Cross guns, Rotorainer, or Turbo Rain irrigators, but they had not thought about this since upgrading to pivot irrigation. Questions were also asked about the impact on the shoulders (particularly in the spring) versus peak of the season. A project update, will be provided to project partners in May 2025 once the spring soil sampling results have been made available.

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December 2024

The projects focus has been ensuring the field trial sites were setup for the 2024-25 season, and post this undertaking the first round of treatments. The field trial sites are located at Essendon Farm - Darfield, Front Row Farm - Ashburton Forks, Pauri Bank Farm - Racecourse Hill, and Prairie Farm - Te Pirita. Each is under a 4 or 5-span pivot irrigator which provides flexibility for the timing of the irrigation treatments. Prior to calving, time was spent with each farm to understand grazing rotations and the irrigation system. This included, undertaking performance assessments of each irrigator and upgrades being made as appropriate, installing 16 soil moisture probes, and understanding the typical grazing pattern and how this may change over the season, e.g., number of breaks, grazing times and grazing rotations and factors that influence these.

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Pre-season soil sampling was undertaken on each farm during July and August (prior to any grazing commencing). The first round of irrigation treatments took place between late September and early October with soil sampling occurring the day before grazing, the day after, and 2-weeks after. Unlike the 2023-24 season the weather allowed all treatments and soil sampling to be completed prior to the end of October. Treatments will now continue prior to each grazing through to the autumn, with the second round of soil sampling also scheduled for this time. The only challenge the project has faced thus far has been the significant rain event of late October. The project team worked with the 2 farms affected to reschedule their grazing 48-hours before or after the event to avoid it impacting the trial sites.

Project communication has included Primary Insight holding 2 irrigation workshops and also presenting at the Lincoln University Dairy Farm focus day. The project and its objectives were discussed at each session. Many farmers commented that they use to 'hold-off' grazing in the past when irrigating with Southern Cross guns, Rotorainer or Turbo Rain irrigators, but they have not thought about this since upgrading to pivot irrigation. Questions were also asked about the impact on the shoulders versus peak of the season. Landcare research recently presented the Year 1 results at the New Zealand Society of Soil Science and Soil Science Australia conference in early December. A project update, including these results, will be provided to project partners in early 2025.

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August 2024

The Year 1 trial field work has been completed, with the end of year soil sampling round taking place in April. Each subplot on the four treatments was sampled immediately prior to grazing, immediately after grazing and two-weeks post-grazing. Results from this round of sampling and an overview of Year 1 will be available in the second half of 2024. Unfortunately irrigation water take restrictions on the Waiau river from mid-February onwards have hampered the running of this treatments during Year 1, with treatments not able to be applied for two grazing rotations. This level of restriction is very unusual on the Waiau river.

Four trial sites have been confirmed for the 2024-25 season, these include one near Hororata, one near Darfield, one near Te Pirita and one at Ashburton Forks. These are presently having their baseline soil sampling undertaken and soil moisture sensors installed.

The projects baseline evaluation has been undertaken through 40 interviews with a cross-section of irrigated pasture farmers, including dairy and sheep and beef, alongside, owners, managers and sharemilkers. Responses demonstrated there is a high-level of awareness amongst farmers around the pugging of soil and its impacts, but a much lesser understanding of compaction and its impacts, the issue which the project is designed to address. The interviews also revealed the majority of farmers used some form of weekly pasture measurement to set their grazing rotation and that >60% of farms still had predominantly manually controlled irrigators on their farm. Around 25% of farms did consider the timing of irrigation and grazing and would typically hold-off a day before grazing where possible. A number of farmers also commented that they use to hold-off a couple of days before grazing when applying irrigation through border dyke or rotary or fixed boom irrigation, but since installing pivots have not done this. Alongside the wait time, information around pasture growth benefits, whether there was a greater impact on the shoulders versus peak of the season and the provision of simple solutions were suggested as useful information that could be provided by the project.

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March 2024

The goal of the project is to develop practical management strategies to measure and mitigate soil compaction from grazing under pasture irrigation. This will provide pasture farms with a range of practical management solutions to allow them to better manage soil compaction resulting from grazing post irrigation.

The year one paddock-scale field trials have been established under a fixed grid irrigation system on a dairy farm in the Amuri Basin. The trial includes 4 treatment sites, irrigation applied 12-hours, 24-hours, 36-hours, and 48-hours prior to grazing. Each treatment encompasses the area between 4 sprinklers and has a soil moisture probe installed to support irrigation decision-making. Decision-support is provided to the farmer on a weekly basis and in the week prior to grazing this increases to daily.

The baseline soil samples for each treatment area were collected in September and included a soil description, penetrometer readings and microporosity cores. The first soil sampling round was completed post the December treatment and again included soil observations, penetrometer readings and microporosity cores. The second soil sampling round is planned for late March/ early April. The actual timing of this will be dependent upon the weather and water availability. An irrigation performance assessment has been undertaken at the trial site to ensure the irrigation system performance is well understood.

The farmer and service industry workshop is planned for May. At this the issues the project is aiming to better understand will be presented. The range of management challenges and potential solutions will then be canvassed with the groups. The project team will use this information to help it develop potential management strategies, and where possible test these as part of the subsequent year’s trials.

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December 2023

The goal of the Improving Soil Health and Productivity under Irrigated Pasture project is to develop practical management strategies to measure and mitigate soil compaction from grazing under pasture irrigation. This will provide pasture farms with a range of practical management solutions to allow them to better manage soil compaction resulting from grazing post irrigation.

The year one paddock-scale field trials have been established under a fixed grid irrigation system on a dairy farm in the Amuri Basin. The trial includes 4 treatment sites, irrigation applied 12-hours, 24-hours, 36-hours, and 48-hours prior to grazing. Each treatment encompasses the area between 4 sprinklers and has a soil moisture probe installed to support irrigation decision-making. Decision-support is provided to the farmer on a weekly basis and in the week prior to grazing the increases to daily.

The baseline soil samples for each treatment area were collected in September and included a soil description, penetrometer readings and microporosity cores. The first soil sampling round was completed post the December treatment and again included soil observations, penetrometer readings and microporosity cores. The second soil sampling round is planned for late February/ March. The actual timing of this will be dependent upon the weather. An irrigation performance assessment has been undertaken at the trial site to ensure the irrigation system performance is well understood.