Grasses and cereal cover crops

Benefits and considerations

Cereals and grasses:

• Exhibit vigorous rooting, develop extensive root systems and establish quickly
• Deliver good early ground cover (important where erosion is a concern)
• Help suppress weed germination and growth
• Produce large amounts of residue and add organic matter to the soil
• Offer a wider range of sowing timings than brassicas or legumes

Sowing times vary with species but often range from July to September. Management is typically similar to autumn cereals and grasses.

Drawbacks and cautions

Grasses and cereal cover crops may act as a green bridge for cereal pests and diseases.

If the cover crop is grown to maturity (to maximise residues), it will reduce the available nitrogen for the next crop. This can be avoided by killing the grass early, applying extra nitrogen or using a legume-grass mix (to supply nitrogen).

Cereal cover crops (as a single species) should not be grown ahead of a spring cereal cash crop. In 2020 research at experimental sites, it was found that spring barley establishment, rooting to depth, and grain yields were all reduced following oat and rye cover crops. Reduction in available nitrogen and the green bridge effect were cited as possible causes.

Cereal and grass species examples

Commonly used grass cover crops include:

• the annual cereals (triticale, rye, wheat, barley, oats)
• annual or perennial forage grasses (such as ryegrass)
• warm-season grasses (such as sorghum–sudan grass)

Winter rye (also called cereal or grazing rye): It germinates quickly, establishes easily and grows readily in the spring. It is very winter-hardy and can be planted later in the autumn than most other species. Decomposing residue of winter rye has an allelopathic effect, helping it chemically suppress weed seed germination. It is often used as a catch crop and works well with a roll-crimp mulch system (in which the cover crop is suppressed by rolling and crimping with crops seeded or transplanted through the mulch).

• Sowing (autumn): Mid-Aug to mid-Sep
• Example sowing rates kg/ha (as a single species): 30–100

Black oats: These are larger and deeper rooting than common oats. In mixture with clover, black oats provide quick cover in the autumn. Summer or autumn seedings are destroyed in winter under most cold-climate conditions. It can provide a naturally killed mulch that may help to suppress weeds. Oat stems also help conserve moisture, even after the plants have been killed by frost.

Annual ryegrass (Lolium): Ryegrass grows well in the autumn if established early enough. It develops an extensive root system and provides effective erosion and leaching control. It adds significant quantities of organic matter to the soil. It may be destroyed in winter in cold climates. However, annual ryegrass is difficult to kill and may become a weed.

• Sowing (autumn): Aug to Sep
• Example sowing rates kg/ha (as a single species): 30-35

Sudan grass: A fast-growing summer annual that suppresses weeds and loosens compacted soil. If inter-seeded with a low-growing crop, consider delaying the seeding of the main crop to avoid shading. Sudan grass produces toxic substances during decomposition, which may suppress plant-parasitic nematodes and other organisms. It can also be used as livestock forage (one or more grazings) and still provide many benefits of a cover crop.
Note: Example sowing dates and rates (where shown) are taken from the AHDB cover crop review.