Soil health management practices in New Zealand vineyards

What is soil health and why is it important?

Soil is recognised for its influential role on both grape quantity and wine quality. While some soil properties are inherent to a location (e.g., soil depth, soil mineralogy, texture), other properties are more dynamic and can change depending on management decisions. For instance, soil fertility, soil water content, and soil structure can be changed intentionally (i.e., adding compost) or unintentionally (i.e., compaction under trafficking).

To maintain the health and function of soils, several interrelated chemical, physical and biological processes are important, and this has prompted a need to consider a wider set of soil indicators beyond more traditional measures of soil water content and fertility alone. However, currently, there is no consensus on the recommended process for measuring soil health, including the most appropriate indicators to use. Furthermore, there is a lack of clarity about what are soil health building practices and the relative efficacy of one practice over another. Bragato Research Institute (BRI) conducted a survey approach to identify practices that are being used by growers across New Zealand to build soil health so we can begin tackling these challenges.

Survey of soil health management practices

A survey questionnaire was completed by 110 growers across 10 grape growing regions of New Zealand and a series of more in-depth interviews were conducted with a subset of 27 growers across seven regions. This article summarises the results from the survey and provides an overview of the work BRI is conducting in subsequent stages of the Soil Health Programme. The survey was distributed in digital format during October and November 2022.

Survey respondents worked on vineyards that were well distributed across small (i.e., <10ha) to large (> 20 ha) properties and comprised predominantly those that grow and make wine to sell under their own label (61) relative to those that grow grapes to sell (29%) or produce bulk wine (10%). Respondents identified their agricultural approach as sustainable (24%), conventional (20%), organic (20%), regenerative (17%) or other (8%). It is acknowledged that participants who took part in the survey tended to have an existing focus on soil health which prevents the generalisation of the findings to all winegrowers and the wine industry.

Drivers for adopting soil health practices

Soil health has been a focus of the winegrowing industry for a long time but there is a possible growing interest in recent years. When growers were asked how important soil health was to them, 96% of respondents indicated that it was important or crucial.

Important reasons why growers were adopting soil health practices were to:

• solve production problems (e.g., alleviating soil compaction, improving water retention and preventing erosion),

• improve soil function (by improving soil biological activity and nutrient availability/cycling),

• increase profitability (by maintaining/increasing yields),

• improve grape quality or reduce inputs (e.g., pest and disease mitigation),

• increase weed control, thus reducing the need for herbicides

• increase insect habitats and activities (bees, native wasps, etc.), boost worm numbers and provide a home for predators,

• ensure the longevity of the vineyard over several years (by ensuring soils remain productive),

• align with their personal values/ support employee well-being.

Barriers to adopting soil health practices

Common concerns of growers when considering soil health practices were the financial risks and a lack of staff capacity. Knowing how to implement practices most effectively was also highlighted. For instance, initial investments into new equipment or materials such as compost or irrigation can be both expensive to purchase and labour intensive to spread, this is particularly evident for undervine management practices such as sowing and mowing.

Difficulty in conveying a strong value proposition for soil health practices was also seen as an adoption barrier especially when changes may be accompanied by lower yields, reduced wine quality (due to increased vigour), increased operating costs or the creation of an impression that vineyards looked ‘unkempt’.

Soil health building practices used currently on New Zealand vineyards

A large proportion (96%) of respondents indicated that they were currently applying soil health-building practices to improve or maintain soil health. A list of these practices along with their adoption frequency amongst respondents is provided (Figure 1). On average respondents were applying seven practices within the vineyard.

The survey indicated that conventional growers tended to favour nutrition and irrigation management over other practices, cover cropping was most common amongst the organic growers while regenerative and sustainable growers were most likely to use cover crops, nutrition and no-till practices. Generally, most survey respondents (76%) were avoiding driving on wet soils and were managing their soil nutrition and applying irrigation. These three practices were also ranked most likely to be successful in improving soil health (or preventing its decline i.e., in the case of avoiding trafficking wet soils).

From the survey results it is difficult to determine what linkage was expected between irrigation management and soil health. For instance, most vineyards rely on irrigation to supplement rainfall and therefore it is a common practice. However, irrigation does not necessarily increase soil health, yet management may be used to avoid compaction, manage weed growth or reduce evaporative losses (i.e., in the case of subsurface irrigation). Similarly, applying nutrients is commonplace (72%), and it is difficult to decipher specific practices that target improved soil health.

In general, interviews conducted with winegrowers identified a notable desire to reduce synthetic fertiliser inputs in favour of organic amendments and fertilisers. A list of organic amendments and fertilisers that are applied in vineyards in New Zealand (Footnote of Table 01).

Soil health practices used in vineyards across NZ and the perceived benefits and challenges of their implementation

Survey respondents were asked what soil health practices they currently use or would like to use along with the benefits they expected to gain from implementing them and the challenges, or reasons why they would not implement certain practices. This information has been summarised in Table 1. It was evident from the survey that participants were uncertain about the trade-offs associated with implementing some practices. For instance, would a certain practice increase tractor passes over time, and therefore it might be negative, or not knowing how to maintain the diversity of cover crops when only a few of the species sown remained.

How to measure soil health status

The type and the number of indicators used by winegrowers in vineyards inform the interpretation of their understanding of soil health. Survey respondents relied most heavily on biological indicators (that include organic matter, soil protein and worm numbers) and on their own instinctual indicators to evaluate the impact of soil health-building practices (81% of respondents in both cases). The third most popular evaluation method among survey respondents was ‘knowledge and experience’, followed by physical indicators (66% and 64% respectively). Findings suggest that more guidance is required on ways to assess soil health and monitor the impact of soil health building practices. As indicated, respondents often rely on instinct and observation to assess soil health and the outcomes of different practices. This might be because of the complexity of measuring soil health and its outcomes, and the lack of consistency among researchers and experts.

While some indicators are used relatively consistently (e.g., organic matter, soil carbon levels) among winegrowers, there are no current key performance indicators that are used systematically in research or in vineyards. As a result, winegrowers might not be able to accurately assess the impact of a practice or capture the evidence that could be used to support decision-making.

Future research

Findings from the study show that research participants are focused on above-ground assets and consider soil a means to an end. Accordingly, many value soil health and are working to improve it if it can directly benefit vineyard operations. However, a lack of clear guidelines and supporting information was a common barrier to adoption. A set of quantifiable key indicators to assess and benchmark soil health is needed as well as greater clarity around the purpose and benefits and trade-offs when considering soil health, especially in the context of cost, resource management (e.g. nutrient cycling and water use) and vine performance.

We expect that decision-making could be supported by the creation of a platform where winegrowers would be able to select their location, soil type and potential issues that might be limiting vine performance, and that could inform them about recommended inputs and practices. Ideally, this would include the financial costs associated with different practices (e.g., labour demands, number of tractor passes) and the estimated return on investment in the form of vine health and yield, grape and wine quality.

The below video talks to some of the survey participants.

Thank you to Yealands and Tohu for contributing to this video.

About the project

This article was summarised by Dr Seth Laurenson, Senior Advisor – Soils and Sustainability at Bragato Research Institute. The survey was led by Bragato Research Institute Programme Manager Michelle Barry to assess what practices winegrowers use to improve soil health. The project was funded by Bragato Research Institute.