Cover crops and water quality

What is the impact of using cover crops? A trial at Strategic Cereal Farm South is testing the effect of using cover crops on soil health, water quality and the following crop.

Cover crops and water quality - trial summary 

  • Start: September 2021
  • End: August 2022

Objective

To assess the impact of cover crops on soil health and on following crop (spring barley) development and health.

Why are cover crops beneficial to arable farms?

Cover crops provide benefits such as improved soil structure, capturing nutrients and providing organic matter.  Cover crops have been used at Wheatsheaf Farming Company since 2010 and all spring crop ground has included a cover crop since 2015. David has since started working with South East Water, FWAG South East and Kings Crops to trial cover crops to reduce diffuse pollution.

How is the cover crop trial run?

This plot trial uses two fields on the farm:

  • Slope field:
    • 24-hectare field
    • Bare stubble (control)
    • Cover crop mix 1 (radish, vetch, phacelia)
    • Cover crop mix 2 (oats, mustard)
    • Cover crop mix 3 (buckwheat, linseed, radish, phacelia)
    • Light loam over chalk
  • Workshop
    • 17-hectare field
    • Control field
    • Light loam over chalk

How are we assessing the impact of cover crops?

Soil assessments

  • Soil health scorecards for each field ( including soil organic matter, pH, VESS, earthworm numbers)
  • Soil mineral nitrogen (SMN)
  • Porous pots

Pest assessments

  • Slug numbers (plot scale)
  • Insect pitfall traps

Crop assessments

  • Above ground biomass
  • Crop development
  • Crop health, yield and quality

The Farm Economics team will calculate the economic cost of production of the crop in each trial field. Using Farmbench, they will produce costs per hectare and per tonne. The calculations will use:

  • Seed, fertiliser and crop protection
  • Farm labour, machinery and equipment

The regional average for property, energy and administration

What results has the project delivered so far?

Soil structure (November assessments)

Bare stubble in Slope field

  • Generally friable and sufficiently well structured
  • Evidence on organic material in soil profile
  • no aggregate cohesion at the surface due to lack of cropping

Cover crop mix 1 (radish, vetch, phacelia)

  • Soil very structured throughout
  • Surface aggregates fine and held together by cover crop roots
  • Bio-pores found in most aggregates

Cover crop mix 2 (oats, mustard)

  • Soil well structured (less so than mix 1)
  • Fewer roots had grown through surface layer
  • Fewer visible bio-pores

Cover crop mix 3 (buckwheat, linseed, radish, phacelia)

  • Worst structred soil of those examined
  • Two distinct layers visible with very compacted deeper layer
  • Roots unable to grow beyond top layer and few bio-pores in lower layer
  • This field zone is closest to the headland 

Winter wheat in Workshop

  • Generally well structured soil
  • Substantial quantities of organic material seen
  • Little cohesion between aggregates at soil surface

All in all, observations in November were similar to those done in October.

Soil Health Scorecard

Key take-aways:

  • Overall earthworm numbers, as well as ratio of adults to juveniles was indicative of a healthy population.
  • VESS score varied between the two fields and cover crops mixes.
  • Differences in K content and percentage organic matter (%OM) between sites were negligible.
  • Mg content differed between Slope field and Workshop.
  • CO2 burst values for all sites are below what would be expected.

Plant counts and ground cover

Establishment assessments have been carried out at all sites 4, 6 and 8 weeks after the drilling of winter wheat in Workshop field. Observations from plant counts and percentage green area scores indicate that:

  • Mixes containing radish provided greater earlier above-ground coverage when compared to areas consisting of cereal species.
  • Individual plant counts appear to decrease past the 4-week mark, but coverage increases – potentially due to competition from broadleaf species.
  • Past the week 5 assessment mark volunteers in the bare stubble begin to offer greater ground cover than the winter wheat in Workshop.

Following destruction of the cover crops, plant-counts and ground cover assessments were again undertaken at 4-, 6- and 8-weeks post-drilling of the following spring wheat. Initially, the spring wheat drilled into the area previously cover-cropped with buckwheat, linseed, radish and phacelia emerged slower than in the previously bare stubble area but as of May 2022 all areas seem to have caught up and are at similar levels.

Soil mineral nitrogen

Soil samples were collected from sites across the four cover crop strips in Slope field as well as from sites in Workshop field in November 2021 and more recently in March 2022.

Analysis by Lancrop on both occasions revealed that soil mineral nitrogen (SMN) was lower in all four strips of Slope field than at sites in the Workshop winter wheat field.

This could potentially be the result of the cover crops taking up ‘plant available’ nitrogen from the soil, whereas the winter wheat crop is sufficiently early in growth such that they have no taken up as much.

Presumably uptake from the cover crops and winter wheat has continued/increased as the more recent results from March 2022 showed further depletions in SMN across the board.

Above and below ground biomass

The above and below ground biomass was recorded for a 1m2 area across each strip of cover crop mix.

  • Where present, oil radish, mustard, oats and phacelia contributed substantially to the above ground biomass.
  • Phacelia was not nearly as prominent in the below ground biomass data.
  • Cereal volunteers in the stubble are also provide substantial above and below ground biomass.

Updates from April crop walk

  • The destruction of cover crops in Slope has taken place and the ground is generally bare
  • Spring wheat drilled in Slope 21st March 2022
  • The winter wheat in Workshop looks generally healthy and was place at GS30

Our Strategic Farms are an opportunity to see how to use our research on a commercial farm. Find out more about our Strategic Cereal Farm South Programme

Image of staff member Fiona Geary

Fiona Geary

Knowledge Transfer Manager - Cereals and Oilseeds

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