Lessons for the management of highly productive land

Two years after Cyclone Gabrielle devastated the Hawke’s Bay and Tairawhiti regions, what have we learned about recovery?

Cyclone Gabrielle struck New Zealand in February 2023, causing widespread flooding that affected Hawke’s Bay, Gisborne/Tairawhiti, and Northland. In Hawke’s Bay and Tairawhiti, Cyclone Gabrielle was characterised by the enormous amount of sediment that was deposited on some of the county’s most highly productive land.

It was an extraordinarily difficult year characterised not by a single catastrophic event but by cumulative impacts from severe storms and several additional weather events including Cyclone Hale in January, Cyclone Gabrielle and Son of Gabrielle in February, and others that followed particularly in the Wairoa and Tairawhiti areas.

In November 2025, we co-hosted with FAR and Vegetable Research and Innovation, a symposium for researchers to share and compare findings from studies of Cyclone Gabrielle and recovery. Around 60 people gathered in Havelock North for two days. Thank you to all the organisations that sponsored the symposium, allowing it to be run with no fees for the participants.

A great deal of semi-coordinated activity followed in the wake of Cyclone Gabrielle. However, there was much incomplete work that would add value by helping enrich our understanding of the longer-term effects of different management responses in different scenarios. The symposium brought together those who investigated Cyclone Gabrielle’s impacts on highly productive land. They presented and discussed findings and observations to draw out lessons to aid land managers and policy makers in future events.

Among the questions were:

1. What are the lessons to pass on to those impacted by future events?
2. What are the lessons for policy makers?
3. What are the economic outcomes from different approaches?
4. How have sites responded to different management of cropping soils, given different sediment types and depths?
5. How have sites responded to the removal of sediment and any subsequent soil amelioration efforts?
6. Have permanent crops responded differently to different approaches applied in similar scenarios?
7. Are all soils recovering quickly? Will they return to previous productivity levels?

Twenty presentations covered historic storm events of note, the weather conditions before and during the cyclone, geological influences, immediate responses, food safety, and longer-term trials seeking to understand how best to return high value land to best production. We thank all the presenters for telling their stories, and all delegates for their contributions to the discussion.

At the end of the symposium, Dirk Wallace led a feedback session in which all delegates responded to a set of questions:

1. What elements aided recovery and what lessons can inform policy and sector planning?
2. What surprises and challenges emerged during recovery?
3. What key takeaways should guide future preparedness?
4. What information is still missing?

Across questions, several themes consistently emerged.

• Communication and collaboration were identified as critically important.
• Data and research surfaced as both a strength and a challenge.
• Infrastructure and preparedness were recurring concerns.
• On the technical front, soil and crop recovery exceeded expectations, with yields rebounding faster than anticipated.
• Finally, human and social dimensions were central to recovery success. Mental health support, patience, and direct communication with experienced peers were repeatedly stressed.

Participants agreed on several priority actions:

1. Establish a central information hub with regional portals to provide consistent, accessible guidance and data.
2. Commission targeted research on rainfall patterns, soil microbiology, contamination risks, and crop-specific recovery timelines, delivered in decision-ready formats.
3. Strengthen pre-event coordination through drills, contact lists, and local decision-making authority, alongside investment in backup infrastructure.
4. Embed human-first supports, including mental health services, peer advisory panels, and tailored financial relief for vulnerable growers.
5. Integrate disaster risk reduction and nature-based solutions (e.g., wetlands, “room for rivers”) into long-term land-use planning.

The symposium captured invaluable knowledge that will help communities and policymakers prepare for and respond to future events. Visit the Cyclone Gabrielle Research Symposium page to access all presentations, with videos coming soon.

Thanks everyone! Sally Anderson, Dirk Wallace and Dan Bloomer – Symposium Convenors

One of the new strips, which is located under the irrigator wire, includes alyssum, calendula, and native ground covers. The other strip which is along a fenceline has the A Lighter Touch annual flower strip mix, which includes alyssum, buckwheat, calendula, cornflower, and marigolds. We also added in a few sunflowers.

The first half of the strip under the irrigator wire has established really well, and both the alyssum and calendula are starting to flower. At the other end of the strip, it is a bit patchy and doesn’t have the same ground cover. Some of the native ground covers amongst the strip have dried out or have been eaten by rabbits, while others are thriving.

The strip along the fenceline consists mainly of buckwheat and sunflowers at the moment, as they were the first to germinate. However, there are patches where alyssum, marigolds, cornflower, and calendulas have also started to establish.

The two biostrips planted in 2024 were made up of 9 different flower mixes, first planted in spring and the second in the summer.

The spring 2024 sowings flowered in the summer but were taken over by grass and clover in the winter. We have mown the strip a couple of times to manage the grass and give the flowers a chance to grow. The alyssum, poppies, borage, and phacelia seemed to do the best in spring 2025 after being mown. Now the strip is mainly grass, clover and alyssum. We have mown it back down again and will track what happens.

The strip planted in summer 2024 and has continued to flower since it was established. Alyssum is the main flower species that has taken over and provided ground cover, but there are areas where there are still cornflowers and calendulas flowering.

There are plenty of insects in the strips and within our butternut crop, but we wanted to understand what insects are actually there and how far they are moving into the crop. To do this, we have set up sticky traps within the biostrips and at various distances into the crop. We will continue to monitor the sticky traps and will try to identify what insects are on them.

We will be holding a grower biodiversity event at the MicroFarm on March 19th. If you are interested in attending, please register here: https://a-lighter-touch.co.nz/biodiversity-grower-group-field-walks/

The Operation Advisory Group has met weekly to observe how the butternuts are growing and to make management decisions for the upcoming week. The main decisions have been about what fungicides to spray, if the Regenerative treatment needs a foliar application, and if a bactericide needs to be applied. Rob Nichol from Horticentre has played a key role in the decision making prosess, helping us identify angular leaf spot in the paddock and providing us with product recommendations.

The first fungicide application went on about a month after planting. Since then, all treatments have had a fungicide and bactericide sprayed each fortnight. With the varying temperatures and rain we have had, it has created the perfect conditions for angular leaf spot, and we have started seeing patches of it within the butternuts.

Table: Fungicide and Bactericide applications to all three treatments in the Carbon Positive Trial.

The Regenerative treatment also had an application of Bio Marinus during the first fungicide application, and a Megafol application the day before the third fungicide.

EIQ is a tool available online through Cornell University, which can be used to determine the environmental impact of specific agrichemicals. The Field Use EIQ is a score based on how toxic the product’s active ingredients are and how much has been used per hectare. The Field Use EIQ Score for each product has been low (around 10). This is why all three treatments have received the same spray applications. For comparison, when the paddocks were broadcast-sprayed with Glyphosate at the beginning of the season, the Field Use EIQ Score was 60.

We will continue to monitor disease pressure and will determine if we can use an alternative product in the Regenerative and Hybrid treatments later in the season.

Throughout the rest of the season, the Operations Advisory Group will continue to meet weekly to make management decisions.

A big thank you to all the Operation Advisory Group members who have attended our weekly field walks.

Carbon Positive is a partnership between LandWISE, the HB Future Farming Trust, McCain Foods, Heinz-Wattie’s and Process Vegetables NZ.

The butternuts in the Carbon Positive trial were planted on the 15th of November. Before the butternuts emerged, there was a high weed pressure in the conventional treatment. Therefore, it was sprayed with Buster, while the other two treatments were not.

Emergence

When the butternuts started to emerge, we noticed there was cutworm damage and found cutworms. Cutworms are one of the main insect pests in butternut crops. They chew through the butternut’s stem at ground level, killing the plant. Once we identified the problem, we sprayed Bestseller before the cutworms did too much damage.

Side Dressing

Before sidedressing, our fortnightly soil nitrate testing showed there was 80 kg N/ha in the Conventional treatment, 71 kg N/ha in the Hybrid, and 62 kg N/ha in the Regenerative treatment.

At sidedressing, the Conventional treatment received the ‘standard’ rate of YaraBela CAN (150 kg/ha). For the Hybrid treatment, the goal was to apply a half rate of YaraBela CAN (75 kg/ha), but the lowest the side dressing machine could be calibrated to was 113 kg/ha, so that is the rate we used. The Hybrid treatment also received a foliar application of seaweed. The Regenerative treatment only received a foliar application of seaweed, Megafol, and fulvic acid, as the soil nitrate results showed there was a sufficient level of Nitrate-N in the soil.

Weed Management

Standard weed management would use an inter-row cultivator before the butternuts start running. We felt there wasn’t a high enough weed pressure to do this, and that it could cause a weed strike if we disturb the uncultivated areas in the Hybrid and Regenerative treatments. All treatments were hand-weeded with a push hoe to remove any weeds before the butternuts started to run.

Operation Advisory Group

The Operation Avisory Group has met weekly, and they are happy with how the butternuts are growing, the low weed pressure and the disease pressure.

A big thank you to Andy for taking the time to side-dress our butternuts.

Carbon Positive is a partnership between LandWISE, the HB Future Farming Trust, McCain Foods, Heinz-Wattie’s and Process Vegetables NZ.

During the tomato crop (26/10/2023 – 6/3/2024), the Regenerative treatment had significantly lower nitrate levels than the Conventional and Hybrid treatments, despite all three receiving similar amounts of nitrogen. This lower nitrate level was likely due to the breakdown of the cover crop. Approximately 12 t/ha of cover crop, mainly oats, was incorporated into the soil two days before planting, which would have tied up nitrogen.

Since then, different amounts of nitrogen have been applied across treatments, and there has been no significant difference in soil nitrate levels, except during the period when the Conventional and Hybrid treatments were in peas, while the Regenerative treatment remained in cover crop.

Amount of Nitrogen applied during each crop, by treatment.

Butternuts

Our pre-season soil tests showed that there was 110 kg of potentially available nitrogen in the Conventional, 93. 3 in the Hybrid and 97.3 in the Regenerative treatment.

Two days before the butternuts were planted, there were 32 kg Nitrate-N/ha in the Conventional, 39 in the Hybrid, and 46 in the Regenerative treatment.

At planting, the Conventional and Hybrid treatments received 300 kg of Complex, whereas the Regenerative treatment received 150 kg of Complex. This increased the kg of Nitrate-N in the Conventional to 80, the Hybrid to 71, and the Regenerative to 63.

At side dressing, the Conventional treatment got 150 kg/ha of CAN. The Hybrid got 113 kg/ha of CAN and a foliar application of seaweed. The Regenerative treatment got a foliar application of seaweed, Megafol, and fulvic acid.

When testing for nitrate after side dressing, we avoided the area where the fertiliser was applied. The nitrate test showed similar results to last time. There is 74 Kg of Nitrate-N in the Conventional, 73 in the Hybrid and 65 in the Regenerative treatment. We can assume the conventional is 18 kg higher and the Hybrid is 13.6 kg higher, as this is how much nitrogen was applied at side dressing.

Our aim is to push the limits of regenerative cropping to understand how much nitrogen input can be reduced. Based on potentially available nitrogen and fortnightly soil nitrate results, the Operations Advisory Group decided not to apply granular fertiliser to the Regenerative treatment at side-dressing.

A similar approach was taken last season in beans, where no granular fertiliser was applied at side-dressing and a foliar approach was used instead. Soil nitrate levels remained similar across all treatments, and the Regenerative treatment produced the highest bean yield.

We will continue to monitor nitrate levels fortnightly, and we will do leaf testing during fruit set.

In November, we co-hosted a research symposium with Vegetable Research and Innovation and the Foundation for Arable Research. The symposium brought together those who had investigated Cyclone Gabrielle’s impacts on highly productive land to present and discuss findings and observations, and draw out lessons to aid land managers and policy makers in future events.

A great deal of semi-coordinated activity followed in the wake of Cyclone Gabrielle. However, there was much incomplete work that would add value by helping enrich our understanding of the longer-term effects of different management responses in different scenarios.

The symposium brought together researchers, advisors, farmers/growers and others involved in observing the impacts on productive land and the effects of different responses in the cases of Cyclone Gabrielle and previous similar events. More than 20 presentations covered historic events, the broader climate context of Cyclone Gabrielle, a range of land use types and many areas of research.

The convenors (Sally Anderson, Dirk Wallace and Dan Bloomer) are now in the process of collating the proceedings and preparing to load material on the conference web page. We’ll do posts as items are loaded with abstracts, summaries and presentation videos. From the outset, the response to the calamity that was Cyclone Gabrielle has been one of high support and collegiality from many, many quarters. The symposium was our attempt to get the best from all the work that was done and find the lessons for those impacted by future events.

We are most grateful for the support and enthusiastic involvement of all the presenters and delegates and the organisations that funded the event.

So far we have calculators for:

• Centre Pivots
• Linear Moves
• Travelling Irrigation
• Solid Set Irrigation
• In-depth Pressure & Energy Analysis

We sent Dan off to keep working on calculators for:

• Multiple Spraylines
• Drip/Micro Irrigation
• a few other ideas!
• and we haven’t seen him for a while

These calculators are based on the 2005 Irrigation Code of Practice for System Evaluation. Its methods have been very well tested over the years and we a proud to have been involved from the start.

The calculators do not store any of your data. The calculations are done in the webpage on your computer and are deleted when you refresh or close the page. That means only you have your data, but if you want to redo things, you’ll have to start again.

Please give us feedback. We are thinking of adapting the Fertiliser Application calculator to this format as well if we get good reviews. And if people want to save their work, we can look into that too.

The Conventional treatment was planted with treated seed and 300kg/ha of Complex fertiliser.

The Hybrid treatment was planted with treated seed, coated in TrichoStart and 300kg/ha of Complex fertiliser. Mycorrcin, Biostart N and TrichoStart were applied at planting via liquid injection.

The Regenerative treatment was planted with untreated seed, and 5kg/ha of humates mixed with 150kg of Complex fertiliser. As with the hybrid treatment, mycorrcin, Biostart N, and TrichoStart were applied via liquid injection.

After planting, all treatments received Ironmax slug bait before two 50cm strips of pre-emergeence herbicide, Frontier-P and Magister, were strip-sprayed over the plant lines.

Throughout the season, the Operations Advisory Group and Heinz-Wattie’s agronomists will meet weekly to track how the butternuts are growing. Together, they’ll make the calls on crop protection, weeding, fungicide and insecticide use, and adjust management decisions as the season unfolds.

A big thank you to Gareth Holder from Redloh Horticulture for taking the time to plant our butternuts.

Carbon Positive is a partnership between LandWISE, the HB Future Farming Trust, McCain Foods, Heinz-Wattie’s and Process Vegetables NZ.

The conventional treatment was broadcast sprayed with glyphosate in mid-October and cultivated in early November. It was disced, then aerated, rotary hoed and rolled. It will be planted with treated seed and 300kg/ha of Complex. After planting, 50cm strips of pre-emerge will be sprayed over the plant line.

The Hybrid treatment was strip-sprayed in mid-September, and was strip tilled at the end of October before being broadcast sprayed with Glyphosate to remove the living strips. It will be planted with treated seed coated in TrichoStart, 250kg/ha of Complex and Mycorrcin, Biostart N, and TrichoStart via liquid injection. It will get sprayed with pre-emerge over the plant line.

The Regenerative treatment was strip-sprayed at the same time as the Hybrid treatment, and before it was strip tilled, a mixture of OMYA Calciprills, Humates, Sulphur, and Boron was applied by drone. This mix has been applied every year in the Regenerative treatment in the Carbon Positive trial when the cover crop is breaking down, before planting. This mix stimulates worms and soil microbiology, which improves soil health. We used 150 kg/ha of OMYA’s Calciprills and 10 kg/ha of Boron as calcium and boron are essential for soil health and plant growth, and it is important that the correct balance is maintained.

Since our soil is naturally low in sulphur and sulphur is slowly released from organic matter decomposition, we applied 10 kg/ha of Sulphur to ensure sulphur will be available to the butternut crop. 5 kg/ha of Humates was applied as it is a microbial stimulant, it stimulates Mycorrhiza fungi, which helps plant roots access nutrients, and it also improves fertiliser efficiency.

It will be broadcast sprayed with Glyphosate to remove the living strips and any weeds that germinated from strip tilling. It will be planted with untreated seed, 150kg of Complex, 5kg/ha of Humates and Mycorrcin, Biostart N, and TrichoStart via liquid injection. It will also get two 50cm strips of pre-emerge over the plant line.

Throughout the season, the Operations Advisory Group and Heinz-Wattie’s agronomists will meet weekly to track how the butternuts are growing. Together, they’ll make the calls on crop protection, weeding, fungicide and insecticide use, and adjust management decisions as the season unfolds.

We are particularly grateful to OMYA for supplying us with the Calciprills, Webster’s Lime for providing us with Boron and Sulphur, and BioStart for supplying us with Mycorrcin. We are thankful for the ongoing support of Heinz-Wattie’s, Gareth Holder from Redloh Horticulture and Hamish Thomas from NH Packing. We look forward to working with them as our butternuts are sown, grown and harvested! Carbon Positive is a partnership between LandWISE, the HB Future Farming Trust, McCain Foods, Heinz-Wattie’s and Process Vegetables NZ.

There are three scopes within carbon accounting: Scope 1, Scope 2 and Scope 3. Scope 1 is direct GHG emissions from sources controlled or owned by a business.  Scope 2 is indirect GHG emissions from electricity purchased by a business. Scope 3, which is broken down into 15 categories, is all other indirect GHG emissions not controlled or owned by a business.

Carbon accounting calculator

We developed a carbon accounting calculator that quantifies the emissions from the different management systems. We are considering making it into a webtool for others to use.

The Scope 1 emissions we considered were fertiliser use, fuel use, and livestock. The Scope 2 emission was from the power used to run the Irrigator. Scope 3 emissions were from the manufacturing and transportation of fertilisers and agrichemicals.

We set the farm gate as our boundary for crops produced, so we have not calculated transport to the factory (the same for all treatments), food processing, sales or home cooking etc. We have included those factors that make most impact and that are within our control. This parallels the Gross Margin accounting we use to assess profitability of the different treatments in our trial.

Emission factors were used to determine the CO2 equivalent (CO2-e) for each operation within the Carbon Positive trial. An emission factor is a coefficient that converts an activity to a greenhouse gas emission. For example, 1 kilogram of non-urea nitrogen has an emission factor of 4.84 kg CO2-e; therefore, you multiply the amount of fertiliser used by the emission factor to determine total emissions.

• The emission factors for fertiliser, fuel use, livestock, and power were all sourced from the Ministry for the Environment: Te ine tukunga: He tohutohu pakihi Measuring emissions: A guide for organisations.
• The fertiliser manufacturing emission factors were sourced from Wells 2001: Total energy indicators of agricultural sustainability: Dairy farming case study.
• The fertiliser transportation emission factor is an average of different fertilisers being transported to New Zealand, sourced from Ledgard & Falconer 2019: Update of the carbon footprint of fertilisers used in New Zealand.
• The emission factors for agrichemicals manufacturing and transportation were sourced from Audsley et al. (2009): Estimation of the greenhouse gas emissions from agricultural pesticide manufacture and use, with original data from Green (1987). Emission factors for the active ingredients were used if available; otherwise, the average value was used for the agrichemical type: Herbicide, Fungicide, or Insecticide.

Carbon accounting calculator results

Over 2022-2025, the first 3 years of the Carbon Positive trial, the Conventional treatment had the highest emissions (5,906 kg CO2-e). The Hybrid treatment (4,401kg CO2-e) was next, and the Regenerative treatment (3,575 kg CO2-e) was lowest. Nitrogen fertiliser followed by fuel were the highest emission sources in all treatments.

In the first three years, only the conventional plots had sheep grazed on them. The other plots were left in ungrazed cover crops. Over later winter 2025, we did have sheep grazing on all three treatments and they will show up in our next update. Note from the chart above, that sheep had about the same emissions as our agrichemicals.