Complete: The effect of cover crops on soil structure and the subsequent sugar beet yield

Timescale: 2015 -2019
Project Lead: Jake Richards PhD student
Project Sponsor: University of Nottingham and BBRO

Project Summary

The project is investigating the effect of autumn/winter cover crops on the physical structure of soil before and throughout the sugar beet crop and how this may influence growth and yield. We will be looking at the growth of cover crops in the UK and how they change soil structure in controlled environments, small-scale trials and also in commercial beet growing situations.

Main Objectives

Main Objectives
• To understand how cover crop species can influence soil structure
• To determine whether the potential changes to soil structure persist into the sugar beet crop
• To investigate whether changes in soil structure, as a result of growing cover crops, affects the growth and yield of the subsequent beet crop

Outcomes / Key Message For Growers And Industry

Key findings for growers:

  • Cover crops can improve soil porosity which can allow better access to water by the sugar beet
    • This effect was seen on a sandy loam soil
    • It resulted in better access to water leading to larger crop canopy and higher sugar yield during the heatwave of 2018 (Fig.1)
    • The greatest effect of this is likely to be seen where cover crops are used in combination with reduced/minimum tillage


  • On heavy soil types cover crop root growth can result in a greater proportion of small aggregates
    • This effect was only measured on heavy soil as soil with higher clay content will take on the shape of roots
    • This effect was removed by power harrowing


  • Looking at the effects of cover crops on porosity and aggregation, cover crop use may be better suited to reduced tillage where the cover crop will have the greatest effect on the system


  • It is well accepted that cover crop success is linked to overall cover crop growth
    • Above ground biomass is a good indicator of the root growth of the cover crops and the influence they have on the soil structure
    • Cover crops should be drilled as early as possible as their growth is hampered if conditions are cool during September
    • There is no evidence that multispecies cover crops are better than single/dual species mixes in terms of root growth


  • Cover crop destruction should allow time for residue break down prior to the sugar beet establishment
    • Excess residue can lead to extreme wet and extreme dry conditions when preparing a seedbed
    • Carbon:Nitrogen ratio of cereal cover crops is higher than brassica cover crops
    • The higher C:N of cereals means they require a longer period to decompose to avoid lock-up of nitrogen intended for sugar beet
    • Brassicas will take less time to decompose and so could be destroyed more closely to seedbed production


  • Sheep grazing was an effective destruction strategy
    • Sheep did not cause compaction of the soil when grazing was carried out on light textured soil when the ground was not at field capacity
    • Grazing is also likely to accelerate the release of nitrogen from cover crop residues and avoid lock-up of nitrogen applied to sugar beet

    • If grazing is to be used on heavy soils this should be done when soils are at low moisture. Compaction can be further avoided by strip grazing




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