Cover crops

Photo credit: Mimi Casteel

Introduction

Some of the key principles of regenerative agriculture are:

  • Avoid bare soil – keep the ground covered
  • Keep living roots in the soil
  • Increase biodiversity

Cover crops / ground cover can help achieve these objectives. Plants in the vineyard (which can be naturally generated and/or sown cover crops) can be grown within vine row alleys, in the under-vine strip, in headlands, and surrounding the vineyard. They can offer multiple ‘ecosystem services,’ such as:

  • Improving soil structure
  • Decreasing erosion
  • Retaining soil moisture
  • Providing habitats for beneficial insects and animal species
  • Increasing carbon sequestration
  • Increasing biodiversity, both above and below ground
  • Providing exudates to feed soil microbes

Soil life depends on having things growing and living in it, and a living soil is best able to furnish the vine with the nutrients it needs and to help build resilience to some diseases.

Crops can be sown into tilled soil, but preferably direct drilled to minimise soil disturbance.

The selection and management of cover crops are highly determined by vineyard location, climate, and soils. Where the opportunity exists to reintroduce beneficial native plant species, this should be the primary choice. In areas with high fire risk, plants with low combustibility should be chosen.


In detail

Cover cropping has been shown to:

  • Increase soil organic carbon through increasing the amount of photosynthetic activity and pulling carbon dioxide from the atmosphere and down into the soils, i.e. sequestration
  • Improve water infiltration, soil aggregate stability and therefore water holding capacity
  • Decrease soil erosion, nutrient leaching and run off
  • Increase biodiversity above ground to improve ecology and provide a range of ecosystem services, including attracting beneficial insects that are predatory or parasitic of problematic insects
  • Increase biodiversity below ground through ‘feeding’ the beneficial microbes in the soil and preserving aerobic conditions, which discourages pathogenic microbes which are generally anaerobic
  • Make the vineyard accessible at wetter times of year
  • Reduce soil temperatures during heat waves
  • Reduce soil compaction
  • Provide opportunity for beneficial plant species regeneration
  • Provide a more attractive beneficial landscape

There is a wide choice of cover crops:

  • Spontaneous sward, allowed to regenerate naturally with native species
  • Perennials, including grasses which mat together as a turf but have high nitrogen demands
  • Annuals which are seeding every year
  • Self-seeding winter annuals in more arid climates

Locally specific vineyard seed mixes are available in some vine-growing regions and where these include native species opportunity for regeneration is enhanced. What is critical is that research and advice is sought to ensure appropriate species are selected and introduced in order to maximise their benefits and reduce competition.

How they are introduced is important too.  The spontaneous sward is allowed to regenerate naturally. However, cover crop seeds can be sown either into pre-prepared cultivated tilth of, preferably, by direct drilling into existing sward. There are increasing vineyard tractor attachment options for direct drilling.

Management techniques vary with climatic conditions, vineyard vigour and machinery availability:

  • Cover crops are now commonplace in the rows of vineyards in many (but not all) wine producing regions of the world, but the adoption of undervine planting or sward maintenance is less common.  In more vigorous regions, undervine low growing cover crops can provide necessary competition but need to be mowed or strimmed regularly to reduce humidity and competitive pressure. Animals such as sheep can be incorporated into the vineyard to control growth but not usually during the vine growing season
  • In the interrow, cover crops are often mowed high, infrequently and in alternate rows, to maintain flowers and habitat for beneficial insects
  • In arid climates, winter cover crops dry out in late spring and can be crimped and rolled to provide a mulch, reducing soil temperatures and reducing evaporation

Competition for water has been cited as a concern, particularly in more arid vineyard regions. Year round ground cover is preferred where possible, as it reduces soil temperatures during heatwaves, increases water holding capacity, and reduces run off and nutrient leaching during extreme precipitation events. However, in warm regions it can be more pragmatic for cover crops to be grown only during the dormant wetter season. They then either naturally die off during the vine growing season or are crimped/rolled to create a mulch, retaining soil moisture and reducing soil temperature. In some very low rainfall seasons it is not possible to establish a cover crop. However, in the long term, improvements in soil structure also increase water holding capacity and reduce run off. Soil moisture monitoring will help alert the grower to any excessive competition and inform subsequent management decisions.

Competition for nutrients between vines and other plant species in vineyards has also been cited as a concern. This is also the case in less vigorous  and newly planted vineyards. In such cases advice from experts/viticulturists should be sought as to the timing, species and management of ground cover/cover crops. The careful choice of cover crops is essential in managing this relationship. For example, nitrogen fixing leguminous cover crops, e.g. clover, can increase availability whereas some grasses have high nitrogen demands.

Concerns regarding competition for nutrients and water in drought conditions are being superseded by evidence that ground cover both reduces temperatures and evaporation and that the roots improve the soil structure so that the soil has a higher water holding capacity.  They also reduce soil erosion and nutrient run off in high rainfall events.

Concerns regarding fire risk require the selection of plants with low combustibility.


Further information