Catch crop trials in Upper Waitaki can reduce nitrogen losses, boost winter feed, and support sustainable farming. Learn how to apply them on your farm.
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Catch cropping to reduce nitrogen loss in the Upper Waitaki
Catch cropping is being trialled in the Upper Waitaki to understand whether it can reduce nitrogen (N) loss to groundwater while still providing useful feed for farmers.
This two-year study is supporting farmers with locally relevant evidence on whether catch crops are a practical nitrogen mitigation tool in cooler Canterbury farming systems.
What is catch cropping and how does it reduce nitrogen loss?
Catch (or cover) cropping can be used as a tool to mitigate nitrogen (N) losses to groundwater following the grazing of winter forage crops.
Fast-growing crops, such as forage oats and short-rotation ryegrass, mop up excess N during the high-risk winter/spring leaching period.
As well as reducing nitrogen loss, catch crops can also:
- improve soil structure
- reduce the risk of runoff and erosion
- provide valuable additional feed for animals.
Researchers from the Bioeconomy Science Institute have studied this N mitigation tool on plots and at farm-scale across Waitaha Canterbury, and other regions.
The research team checking the trial catch crops
Why catch cropping matters in the Upper Waitaki
Catch cropping has not previously been studied in the Upper Waitaki. We’re supporting a two-year study by Bioeconomy Science Institute researchers to understand how different catch crop species might perform in this cooler climate.
This area-specific study is important to determine whether catch crops are a viable option to help mitigate losses in farm systems in the Upper Waitaki.
Researchers are:
- Liaising with local farmers and catchment groups to better understand their winter forage cropping systems
- Sharing current science-backed knowledge around good N use practice
- Establishing and studying catch crops on three farms in the Upper Waitaki over two seasons
What makes catch cropping successful?
Learnings from previous studies and Year 1 of the Upper Waitaki trial show that successful catch cropping relies on:
- Sowing as early as possible after winter grazing
- Selecting winter-active species such as cereals (forage oats, oats + Italian or tetraploid hybrid ryegrass)
- Targeting recommended sowing populations (300 plants/m² for cereal; 110–120 kg oats/ha at 3–4 cm depth)
- Using minimum or no tillage, with surface tillage where soils are compacted, uneven/pugged and/or have high surface residue
- Controlling weeds appropriately during establishment
- Not applying nitrogen at sowing (with some N fertiliser potentially required later, e.g. 40–50 kg N/ha after canopy closure)
- Harvesting at the ‘booting stage’ to balance yield and quality
Together, this trial and its learnings aim to provide farmers in the Upper Waitaki with locally relevant information to support informed decisions about catch cropping.
Year 1 trial methods and results
What was done
From August to December 2025 three farms within a 20-minute radius of Omarama participated in Year 1 of the trial. Each farm established demonstration plots after winter forage grazing using:
- Forage oats (Crowa)
- Oats + Italian ryegrass (Tabu)
- Oats + tetraploid hybrid ryegrass (Shogun)
A part of the catch crop demonstration was a fallow strip to measure the impact of the catch crops on reducing the risk of N losses from conventional practice. In addition, 100 m transects were established in each paddock to more generally monitor the flows of N through the winter forage crop-fallow rotation. The results of this will be available in due course.
Sampling methods
Sampling of the soil N level and crop yield were done in:
- First sampling and planting of crops: August or September 2025 (post-grazing; soil only)
- Second sampling: November 2025 (catch crops)
- Third sampling and crop harvest: December 2025 (catch crops)
Summary of Year 1 findings
Results from Year 1 suggest catch crops could have a place as a mitigation tool in reducing the risk of N leaching in the Upper Waitaki environment.
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Catch crops were sown in daily average soil temperatures (recorded at 5 cm depth) above the recommended minimum sowing temperature of 4 degrees.
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At green-chop silage in early December, final yields ranged across the properties from between 2.7 and 9.3 t DM/ha, with the lowest yields recorded at the highest altitude.
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In Year 1, catch crops reduced the amount of soil N at risk of leaching in the Upper Waitaki.
Note: This study measures soil N before and after catch cropping to assess the N leaching risk profile (not N leaching per se). In other studies involving measurements of N leaching, this reduction in soil N by catch crops has been shown to significantly reduce the amount of N leached.
View detailed trial results for crop yield and soil nitrogen
Farm 1 - Sheep station
- Elevation: approximately 350 m above sea level
- Previous crop: kale
- Soil type: Mackenzie loam (Pallic Orthic Brown, shallow)
Crop yield results
| Crop | Yield on 11 November 2025 (t DM/ha) | Final yield on 4 December 2025 (t DM/ha) |
|---|---|---|
| Oats | 2.41 | 8.13 |
| Oats + Italian ryegrass | 2.48 | 9.33 |
| Oats + Tetraploid | 2.09 | 8.73 |
Summary of results: Farm 1 recorded the highest overall yields across the three sites. Final yields ranged from 8.13 to 9.33 t DM/ha, with the oats + Italian ryegrass mix producing the highest yield at harvest. Growth between November and early December was substantial across all treatments.
Soil nitrogen results
| Crop | Soil N at 0-30 cm before catch crop (25 August 2025) | Soil N at 0-30 cm on 11 November 2025 | Catch crop N uptake by 11 November 2025 |
|---|---|---|---|
| Oats | 62 | 17 | 61 |
| Oats + Italian ryegrass | 81 | 15 | 59 |
| Oats + Tetraploid | 111 | 18 | 44 |
Summary of results: At Farm 1, soil nitrogen levels (0–30 cm depth) decreased substantially between August and November across all treatments. Catch crop nitrogen uptake by mid-November ranged from 44 to 61 kg N/ha, indicating significant removal of soil N during early crop growth.
Farm 2 - Dairy farm
- Elevation: approximately 350 m above sea level
- Previous crop: fodder beet
- Soil type: Larbreck sand (Typic Orthic Recent, shallow)
| Crop | Yield on 11 November 2025 (t DM/ha) | Final yield on 4 December 2025 (t DM/ha) |
|---|---|---|
| Oats | 2.64 | Crop terminated |
| Oats + Italian ryegrass | 2.78 | Crop terminated |
| Oats + Tetraploid | 2.51 | Crop terminated |
*Crop was terminated before final measurements were able to be taken.
Summary of results: At Farm 2, November yields ranged between 2.51 and 2.78 t DM/ha across treatments. Crops were terminated before final harvest measurements were taken, so total seasonal yield could not be determined. Despite early termination, all treatments showed similar growth up to November.
Soil nitrogen results
| Crop | Soil N at 0-30 cm before catch crop (25 August 2025) | Soil N at 0-30 cm on 11 November 2025 | Catch crop N uptake by 11 November 2025 |
|---|---|---|---|
| Oats | 59 | 9 | 58 |
| Oats + Italian ryegrass | 77 | 8 | 76 |
| Oats + Tetraploid | 74 | 5 | 59 |
Summary of results: At Farm 2, soil nitrogen levels declined markedly across all treatments between August and November. Catch crop nitrogen uptake ranged from 58 to 76 kg N/ha by mid-November, with the oats + Italian ryegrass treatment showing the highest uptake.
Farm 3 - Sheep station
- Elevation: approximately 620 m above sea level
- Previous crop: kale
- Soil type: Rhoboro silt (Acidic-weathered Fluvial Recent, shallow)
| Crop | Yield on 11 November 2025 (t DM/ha) | Final yield on 4 December 2025 (t DM/ha) |
|---|---|---|
| Oats | 0.64 | 3.75 |
| Oats + Italian ryegrass | 0.59 | 2.78 |
| Oats + Tetraploid | 0.79 | 2.68 |
Summary of results: Farm 3, located at the highest altitude, recorded the lowest final yields. Final yields ranged from 2.68 to 3.75 t DM/ha. The oats treatment produced the highest yield at this site. Cooler temperatures and elevation likely influenced overall crop performance.
Soil nitrogen results
| Crop | Soil N at 0-30 cm before catch crop (25 August 2025) | Soil N at 0-30 cm on 11 November 2025 | Catch crop N uptake by 11 November 2025 |
|---|---|---|---|
| Oats | 16 | 9 | 17 |
| Oats + Italian ryegrass | 46 | 10 | 16 |
| Oats + Tetraploid | 71 | 11 | 20 |
*Note: high variability in results is due to demonstration plots only, i.e. no replication
Summary of results: At Farm 3, soil nitrogen levels were lower overall compared with the other sites. Catch crop nitrogen uptake ranged from 16 to 20 kg N/ha by mid-November. While uptake was lower than at the lower-altitude farms, soil N levels still declined across treatments.
Key findings for Upper Waitaki farmers
- The trial is running over two seasons so farmers have more information to base potential decisions about growing catch crops on.
- In Year 1 of the trial, researchers found catch crops put on most growth during November. This is when farmers in the area might be looking to use paddocks for sowing the next main crop such as another winter forage crop or pasture.
- Most of the environmental impact of the catch crop happens during early to mid-spring.
Protecting and enhancing the Ahuriri and Upper Waitaki catchment: Learn about the work that is underway supporting healthier soils, waterways, and farming systems