Cover crops improve soil structure

Roots support soil biology

• Root exudates provide food for microorganisms
• Microorganisms produce polysaccharide gums that ‘glue’ soil aggregates together
• Many cover crop species support soil mycorrhiza populations between cash crops
• Mycorrhizal fungi are important in phosphorus nutrition
• Brassicas, sugar beet and lupins do not support such populations (non-mycorrhizal)

Roots stabilise soil structure

• Vigorous root systems bind the soil, so wind and water erosion is substantially reduced
• Extensive fine roots bind the soil and stabilise aggregates
• Some species produce deep tap roots that help break up compacted soil
• Rooting increases soil macroporosity (the proportion of large pores in the soil that provide air supply to roots) by providing continuous channels
• Increased soil organic matter content can improve water-holding capacity

Cover crops to improve soil structure

Assessments of soil structure can reveal underlying problems, including the target depth for management: shallow (0–20 cm), deep (20–40 cm) and very deep (>40 cm).

Autumn cover crop (followed by a spring crop)

Target depth: shallow

Suitable crops include cereals, brassicas, legumes and other broadleaf species. Consider mixes with complementary rooting depths.

Target depth: deep

Brassicas and possibly other deep-rooted broadleaf species. Consider mixes, particularly if other depths are of interest.

Target depth: very deep

Avoid short-duration cover crops.

Spring cover crop

Target depth: shallow

Cereals, legumes (e.g. trefoil or vetch) and broadleaf crops (e.g. phacelia or brassicas). Consider mixes with complementary rooting depths.

Target depth: deep

Brassicas are potentially useful at these depths (e.g. radish). Consider mixes, particularly if other depths are of interest.

Target depth: very deep

Avoid short-duration cover crops.

Full season fallow

Target depth: shallow

Suitable crops include cereals, brassicas, legumes and other broadleaf species. Examples include oats, phacelia, mustard or radish (potentially in mixes). In addition, legumes (such as trefoil or crimson clover) provide an opportunity to fix nitrogen in spring.

Target depth: deep

Brassicas (e.g. mustard or radish) and some legume species.

Target depth: very deep

Potentially brassicas and some legume species (e.g. lucerne or sweet clover).