Building momentum on national agrichemical priorities
27 February 2026
New Zealand study tour recap: Insights from vegetable grower participants
27 February 2026
Reading Time: 5 minutes
A year of trials at the Soil Wealth and Integrated Crop Protection (ICP) Oakdale demonstration site is testing how legume and cereal cover crops, combined with reduced tillage, can better align nitrogen release with brassica crop demand – cutting inputs, improving efficiency, and delivering practical benefits for growers.
It was a busy year at the Soil Wealth and ICP project Oakdale demonstration site, which aims to explore how legumes can be effectively used to supply nitrogen to a brassica crop.
Steph Tabone (Applied Horticultural Research), who is leading trials at this site with grower Phil Bartolo, is putting theory into practice to test whether it is possible to align the nitrogen release from cover crops with the crop’s nitrogen demands.
“This trial combines many things, including cover crop management, termination methods and soil preparational with the aim of optimising nitrogen cycling and reducing inputs,” Steph said.
Overview and objectives
At the Oakdale site, the team has been testing three cover crop treatments – straight oats, a mix of oats and faba beans, and a bare fallow control.
Cover crops were terminated using a combination of herbicide at flowering stage and rolling/crimping down of the biomass.
To prepare the beds to the brassica cash crop, three approaches have been tested:
- Speed discing
- Strip rotary hoeing
- Full rotary hoeing (the control)
These methods were selected to balance the goals of reduced tillage to support soil health, while providing practical benefits for the grower, including time savings, lower diesel use, reduced spraying for weeds and decreased tractor maintenance costs.
Seven treatments are being tested:
- Fallow + speed disc (the control)
- Faba and oat cover crop + speed disc
- Faba and oat cover crop + strip rotary hoe
- Faba and oat cover crop + full rotary hoe
- Oat cover crop + speed disc
- Oat cover crop + strip rotary hoe
- Oat cover crop + full rotary hoe
Trial activities to date
Activities at the Oakdale demonstration site began in May 2024, with soil nutrient and biology assessed prior to planting the cover crops in August 2024. Biomass assessments of the cover crops were conducted in November 2024, followed by termination of the cover crops in December 2024 using a combination of roller crimping and herbicide application.
Soil available nitrogen (ammonium and nitrate) was monitored throughout the year to track changes as cover crop residues decomposed. Above-ground cover crop residues were also measured for quantity and quality during the same periods to investigate residue breakdown over time.
In June 2025, soil was prepared using the three different bed preparation methods, with reduced-tillage approaches such as the speed disc and strip rotary hoe offering faster tractor operation and lower input costs compared to full rotary hoeing. Cabbage was transplanted into the prepared beds soon after.
Further soil assessments conducted mid-year measured soil hardness, water infiltration, and bulk density at 10 cm and 30 cm depths.
Cabbage tissue testing in September 2025 monitored nutrient status, with a focus on nitrogen, alongside measurements of soil water infiltration. Post-harvest soil tests and crop yield data were collected in mid-November 2025.
Fertiliser was applied following the grower’s standard practice, with a base application at planting, and side dressing at five weeks after transplanting and again at the pre-heading stage.
EARLY RESULTS AND INSIGHTS
Cover crop performance
Before termination, the faba bean and oat mix contained 217 kg N/ha in aboveground biomass, while straight oats held 156 kg N/ha. Following termination, soil available nitrogen ranged from 17-24 kg N/ha across the treatments in December 2024 but decreased to 5-7.5 kg N/ha by May 2025, six months after residues were left on the surface.
Cover crop residue biomass and nitrogen content declined significantly over this period.
The cabbage crop
The cabbage crop performed very well across all treatments, with only subtle visual differences.
Tissue testing at the pre-cupping growth stage indicated adequate nitrogen levels in all treatments, although slightly lower total nitrogen was observed in cabbages planted into strip rotary hoe beds.
Yield data were relatively consistent, with the highest average head weights recorded in the faba-oat cover crop planted on speed-disc-prepared beds.
L-R. Bulk density assessments, March 2025. Cabbage under faba oat full rotary hoe treatment, July 2025.
Cost and efficiency gains
While crop performance and yield were similar across treatments, the greatest benefits have come from reducing tillage through speed disc use. This method has saved time, reduced diesel consumption and decreased tractor wear compared to conventional rotary hoeing.
Using cover crops and terminating them with roller crimping (leaving residues on the surface) has also reduced the grower’s herbicide use by 50 percent, as cover crops suppressed weeds and reduced tillage minimised soil disturbance, limiting weed seed germination.
Nitrogen dynamics and other lessons
Monitoring nitrogen levels after roller crimping showed a gradual decline in soil and residue nitrogen between December 2024 and cabbage planting in June 2025. In response, grower Phil has experimented with mulching and incorporating cover crop residues 4–8 weeks before planting, rather than leaving residues on the surface for 6–12 months, to better optimise nitrogen.
Early attempts highlighted challenges incorporating the high biomass using a speed disc, prompting adjustments. Residues are now mulched, left to decompose slightly, then incorporated.
The next steps will involve optimising the timing of mulching, incorporation and planting to further improve nitrogen use efficiency.
“Once this is better understood, we can perhaps reduce base fertiliser nitrogen to account for nitrogen supplied by legume cover crops,” Steph said.
“A full analysis of soil hardness, bulk density, water infiltration, crop yield and economic outcomes is currently underway.”
“We look forward to getting a clearer picture of what is working best for the grower, including an economic and soil health analysis.”
An in-depth case study will be prepared and published on the Soil Wealth ICP website, providing further insights and recommendations for growers.
Acknowledgements
The team extends its thanks to grower Phil Bartolo for his engagement and ongoing efforts to host the demonstration site.
Team planning and professional development
In January, the team held a two-day planning session to ensure the Soil Wealth ICP project continues to deliver value for vegetable growers in 2026. The team focused on the demonstration sites, events and training, resource development and communications activities, and explored four focus topics for the coming year.
They include:
- Soil health
Biology and microbiome - Crop health:
Integrated pest, disease and weed management - Input use:
Waste - Carbon and climate:
Resilient production systems
The team also visited the Oakdale (NSW) demonstration site hosted by Phil Bartolo, which is focusing on optimising nitrogen supply for a brassica crop through strategic use of legume and cereal cover crops.
The field visit included a technical training session on nutrient management with agronomist Mike Titley – find his tips for cabbage plant tissue sampling on the Soil Wealth ICP website.