Feeding the soil that feeds us (Part 2)

Part Two – Think global, act local: Challenges and opportunities for compost use in New Zealand

Written by Kate Walmsley and Elena Izaguirre, members of the WasteMINZ Organic Materials Sector Group Steering Committee

While composting has been well-established in NZ, significant volumes of organic waste still go to landfill, presenting a substantial opportunity for diversion of this material for beneficial reuse on vineyards, horticulture, and agricultural production, while reducing landfill emissions. As discussed in the previous article, compost use on productive land is seen as a tool to improve soil health, and regenerative practices are becoming more mainstream. However, there are some key challenges that face the commercial horticulture and agriculture sectors when it comes to sourcing, using and applying compost.

The Leaderbrand trial in Gisborne highlighted a number of barriers to overcome when using compost within a complex vegetable production system. A key emphasis is ensuring a consistent supply of high-quality product, which is critical for the success of the crop and confidence of the grower. Often it can be difficult for a grower to find a nearby supplier that can deliver the volume of compost they require. This brings into play other issues, such as the cost to transport the compost to the site, which can mean it is only financially viable when the compost is from the local area. A commercial grower must also adhere to legislative food safety requirements, such as withholding periods that stipulate how long before harvest compost needs to be applied to ensure the crop meets food safety standards. It was also acknowledged that there is added complexity compared to conventional fertiliser when using compost, such as its supply chain, storage and nutrient release, and any nutrient caps in local Regional Council Plans.

Similar challenges, such as the cost of transport, are experienced in the wine industry. Further, as compost is a soil conditioner, it can take time to recognise the direct benefits from application. As soil improvements can be difficult to quantify and occur slowly, compost can become a ‘nice to have’ due to cost, time and resourcing pressures, says Massey. The issue of scale is another key issue; if growers are making compost onsite, they will need a facility or space large enough to produce the volume of compost required whilst maintaining environmental compliance, for example leachate containment, which can be expensive and carries its own carbon footprint.

 Industrial Composting Site with Machinery in Operation in the UK.Image Credit - Mark Stebnicki

This expectation from the horticulture and commercial growers’ market sets a challenge for compost producers to consistently deliver high-quality compost that has low contamination and a good nutrient profile at the right price. Jaco Kleinhans, National Organics manager at WM New Zealand, and Liz Stanway, Organics Team Leader at Xtreme Zero Waste in Raglan, describe the complexities of producing compost at the large commercial scale and the medium scale: While ensuring product quality and consistency, they must balance the costs of production, source clean, quality feedstock, and ensure environmental compliance for the business. Proximity to customers is vital for compost producers due to transportation costs. Because compost is very different from a conventional fertiliser, it is important that the compost producer offers dedicated customer service for their commercial end users, including technical guidance and support in all aspects of their compost journey.

A major issue for all composters is managing the contamination that arrives with the organic feedstock. Physical materials like plastic, glass, and metal are difficult to remove, while invisible contaminants—such as heavy metals, PFAS, and microplastics—pose deeper challenges and can compromise the quality of the final compost. Contamination needs to be addressed before organic materials are sent to composters, as it’s much more effective to separate out contamination “at source” than at the composting plant.

Microplastics are just one of the contaminants encountered in compost. IMAGE CREDIT: Shutterstock

With the recent emphasis on sustainability practices, there are now financial incentives for large compost producers and commercial end customers to reduce their carbon footprints, such as getting better rates on loans with proof of substantial emissions reductions. These emissions reductions could come as a result of the compost producer diverting organic waste from landfill or a grower replacing a portion of synthetic fertiliser—which is emissions-intensive to produce—with compost, or a compost–fertiliser blend, which enables a more affordable single application to soil. All of these challenges present a range of opportunities for decision makers, compost producers, the wider organics processing sector, as well as farmers and growers, while building national resilience to global instabilities.

Compost producers and the organic materials sector

• Kleinhans stresses that the compost market is moving faster than ever before, and care must be taken to keep the composting sector moving ahead and avoid running into common issues. Composting infrastructure and locations must be selected carefully, operators must be responsible, and environmental assessors must be well trained.
• Producing high-quality compost through the whole supply chain is of utmost importance. By setting high standards for input material, this sends a signal that only clean, contaminant free feedstock will be accepted for composting. Behaviour change work with people and companies using organics services is key.
• Reviewing the current voluntary compost standard. A recent Eunomia report noted that the NZ composting standards are outdated and that the landscape has changed substantially, from contaminants of concern to processing technologies.
• Expanding the end market for compost through collaborations with other stakeholders, such as fertiliser companies.
• Minimising the high transport costs by back-loading where possible, and securing storage close to end markets.

Research & education

• There is a need for more science-backed soil health trials in the NZ context, but Norris notes that getting funding is difficult, especially for long-term studies.
• A new research and demonstration farm has been set up in Pukekohe by Te Ahikawariki/Vegetable Industry Centre of Excellence, enabling researchers to push boundaries without pressure on the resulting crop, and to share findings with all growers instead of being hidden by IP.
• The value of compost is well understood in some of the larger commercial grower markets, but more needs to be done to bring on board a wider catchment of industry organisations, for example intensive vegetable growers. Merfield says the key challenge in improving soil health is getting compost use and growing practices effectively communicated to and implemented by farmers/growers. To do this, more specialist extension services, funding and people who can bridge the farming and science worlds are necessary.
• Many growers are change- and risk-averse; integrating compost use into their systems requires sustained behaviour change with trusted messengers. It is important to get early adopters on board and back up claims with good science. Norris also noted the relevance of social research in supporting behaviour change.
• There is enthusiasm among growers for making their own compost onsite, which is ideal in terms of closed-loop nutrient cycling. However, there’s a knowledge gap when it comes to putting this into practice, presenting opportunities for closer collaboration between growers and specialist extension services.
• At the local and home gardener level, education is still important when it comes to expectations around using compost.
  

Commercial growers

• When it comes to making a measurable difference to supporting wine growers in their use of compost, Massey suggests a regional development fund for areas that have a large stream of organics needing amelioration. “We do understand that central government funding is at a premium, but there are regions where a broad range of agricultural land uses and cross-industry cooperation will yield benefits to the wider community, make better compost and get as much ‘waste’ as possible activated and back where it came from. Working with the government on the issue certainly makes sense.”
• Industry- and context-specific regional groups of growers are established to streamline practices, create shared research objectives and engage on sustainability matters. This is already proving successful, from the larger scale with the Vegetable, Research & Innovation Board, to the local with the Marlborough Circular Wine Group, a group of large and small wine companies in Marlborough supported by Marlborough District Council.

 Oil tanker at sea. Image credit:  - Ian Young

The escalating conflict in the Middle East has disrupted a critical supply chain route for New Zealand, as a significant proportion of the oil and urea we use passes through this region. As a result, our primary sector is facing not only increasing fuel costs for harvesters and transport, but also increasing costs of imported synthetic fertilisers. These external pressures highlight the vulnerability of relying on sometimes-volatile international markets for essential farming inputs.

In this environment, shifting toward locally produced compost offers a strategic advantage for resilience: reducing dependence on imported fertilisers through the beneficial reuse of local organic waste streams, thus lessening exposure to fluctuations in global energy supply chains.

Stanway describes how the combined impact of lockdowns and extreme weather in recent years has highlighted the vulnerability of our food systems, leading residential and independent growers to recognise the vital importance of resilience, healthy eating, and the cost savings of growing their own food. This has triggered a spike in compost demand as people look to insulate themselves from global instability and a changing climate.

There is huge opportunity in NZ to move towards compost as a tool for improving soil health and reducing synthetic fertiliser use, while reducing emissions from the primary sector and organic waste in landfills, and building resilience to global supply chain shocks and increasingly frequent extreme weather. To seize this opportunity, more NZ-specific research, thoughtful planning and investment, improvements in the consistency and quality of compost products, and cross-sector collaboration are needed.

Missed Part One: About soil, developments in soil science, and a snapshot of compost use in NZ - you can read it here