Grass leys for the arable rotation

There are many ways grass can be used within the arable rotation. Read about the types of grass ley, and the benefits for black-grass control. 

Leys can be utilised in various ways:

• Grazing rented out for a season or for the life of the ley
• Standing crops sold to others to make silage or hay (this can be done for the whole season or for particular cuts and tend to be sold on a per hectare basis)
• Contract-grown crops (e.g. lucerne) for other companies that may look after the agronomy and harvest
• Livestock owned by others graze the land, but the landowner has responsibility for looking after the stock (this can be done on a liveweight gain or pence per day contract)
• Silage made by the landowner and sold to local farmers or to anaerobic digestion plants (can be sold on a fresh weight/dry matter basis or on quality)
• Livestock bought by the landowner to graze the crops or eat the conserved silages or hay

Leys can be a useful addition to an arable rotation, particularly to manage weed problems, such as black-grass, or to build soil fertility.

Types of ley

Leys tend to be made up of mixtures (including grass, clovers or herbs) and are often in the ground for at least one season. Common options include fields of lucerne or red clover and cutting grasses. The latter may be Italian or hybrid ryegrasses, which produce a significant yield in the first two years but should then be replaced.

Long-term leys (up to five years) are often made up of grasses and clovers, with the option of adding additional herbs, such as chicory and plantain. Although these can be cut, they are more often grazed for most of the year.

It is important to select the right type of grass and clover for the purpose of the ley because this will affect seed costs and how long the mixture will last. Specialist silage leys require the least amount of time in a rotation.

Typically, for white and red clover, it takes around one year for the quoted levels of nitrogen to be fixed – up to 150 kg N/ha for white clover and up to 250 kg N/ha for red clover. Therefore, clover can be difficult to justify in a short-term ley.

However, clover improves feed quality for livestock, with high growth rates and protein content in silage. Annual clovers, such as berseem and crimson, fix nitrogen in the first year but tend to die away during the winter.

Most of the nitrogen is within the growth, which will be returned to the soil as the plant decays or through the dung and urine of grazing animals.

Grass variety selection

Variety selection is key when establishing grass. Some varieties perform better under silage than grazing and vice versa. Consequently, it is important to consider whether the grass ley will be mostly cut or mostly grazed because selecting the correct variety can have a significant impact on financial returns.

The AHDB Recommended Grass and Clover Lists (RGCL) provides an independent testing system to ensure the best grass and clover varieties are available for selection.

Grass establishment

The timing of grass establishment is flexible. Typically, grass can be established anytime between April and September, so long as soil moisture is not limiting.

Grass leys are most likely to be established in arable rotations in the autumn, after harvest. This allows the seedbed to settle over winter and a good structure to form. However, if grass is established this late in the season, weed competition can be significant, and there can be a narrow window for good establishment. Grass leys can also be established in the spring after over-wintered stubbles or a cover crop.

Turning over arable fields to grass can be a highly effective way of reducing the black-grass burden on a field.

Black-grass seed is relatively short-lived in the soil, with seed number declining by approximately 70% each year. There is no evidence that this rate varies with soil type or soil moisture. Therefore, if black-grass seed return is prevented by cutting or grazing a grass ley, the seed bank declines rapidly. Where the seed bank contains substantial numbers of black-grass seeds, even after several years under grass, there will still be a substantial number of viable black-grass seeds in the soil.

Black-grass palatability

Black-grass has low palatability for livestock, and the amount of black-grass in the sward should be minimised. If the preceding arable crop had a high black-grass burden, then ploughing is recommended to bury the seed below the germination depth.

Delayed drilling of the ley in the autumn, until after the peak black-grass germination period, or drilling in the spring, will further reduce the number of black-grass seeds germinating in the grass sward. In either case, cultivations should be used to prepare a sterile seedbed, which can be managed with further cultivation and glyphosate.

Minimising soil disturbance when drilling the ley will minimise any black-grass germination. There are no herbicide options for controlling black-grass in the ley if it is to be used for grazing or conserved herbage.

Returning to arable production

When returning the grass ley to arable production, some viable black-grass seed will still be in the soil. Soil disturbance will stimulate this seed to germinate. Consequently, spraying off the grass sward with glyphosate and direct drilling is likely to result in the lowest black-grass population in the first crop following the grass.

Winter wheat may be the preferred first cropping option to exploit the soil fertility built up during the ley. However, longer leys will have a higher burden of pests that will attack wheat (e.g., frit fly and leatherjackets).

Increased seed rates can reduce the impact of these pests, but oilseed rape (OSR) or beans may be a better option for the first crop after a longer ley, although soil moisture can be an issue for autumn-sown OSR after a vigorous grass ley. Maize is also an option after grass, with the potential to sell this following crop.

An initial spring crop will minimise black-grass in the first crop after the ley. This can reduce the soil pest burden if the ley is destroyed in the preceding autumn. Whichever crop is used immediately after the ley, a robust pre-emergence herbicide programme should be used to tackle any surviving black-grass.

An integrated weed management approach to black-grass should be used. Incorporating cultural control options, such as delayed drilling, spring cropping and appropriate cultivations, will be required to prevent the black-grass populations from increasing rapidly again, particularly where herbicide resistance is present.

Yields

Leys should be treated like an arable crop, with good soil structure and nutrient supply to ensure yields are maximised. The world record for dry matter (DM) yield of grass is around 25 t DM per hectare.

Yields in the Recommended Grass and Clover Lists trials tend to be around 16–18 t DM per hectare under cutting regimes, with newly sown plots and with high levels of nitrogen being applied. The target for commercial grazing systems in the UK and Ireland is to utilise 10 t DM per hectare.

The need for multiple harvests, through cuts or grazing, means it is crucial to focus on utilisation because this has an important impact on the cost of production. Utilisation can vary from 50–80%. Improved utilisation is linked to investment in infrastructure (e.g. fencing systems for grazed swards or machinery for cutting systems) and allocation of labour.

DM is the most common way of expressing grass growth, as it accounts for differences in the water content at different times of year.

Costs

As with all crops, understanding production costs is crucial to ensuring the enterprise is profitable. This example calculates the cost of silage.

Step 1

Work out costs on an area basis:

• Rental value – Everything grown on a farm carries a rental value. Land could be let for a standard figure of, e.g. £250/ha/year if it’s not used to grow a silage crop. First-cut grass normally produces 40% of the total annual yield
• Establishment and grassland management – On average, reseeding costs are £250/ha* (£50 a year for a five-year ley). Allocate 40% to first-cut silage. Include weed control expenses on the same basis
• Inputs – Limited on grassland, but with key crops, like maize, include appropriate costs (e.g. sprays and plastic)
• Machinery – Most contractor operations are easy to allocate on an area basis. The calculations can get more complicated when the farm makes its own silage. Use contractor prices as a guide
• Other costs – These include additives, sheeting and analysis and are usually recorded on a per-clamp basis

Simply divide the total by the area going into the clamp. *Full reseed, including ploughing = £375/ha. Overseeding = £175/ha.

Example: (40 ha, first cut, 68 D-value) Costs/ha £250 × 40% = £100 Reseeding costs = £20 Fertiliser (400 kg of 20:10:10) £270 × 40% = £108 Slurry application = £49.50 Rolling = £26 Fertiliser spreading = £5 Mowing = £12 Tedding/rowing = £19.50 Carting/clamping = £128 Additive = £800/40 ha = £20 Sheet and analysis cost £120/40 ha = £3 Total/ha = £491

Step 2

Estimate the yield – see page 16 on how to calculate silage stocks

Step 3

Work out costs (pence per kilogram of DM (p/kg DM))

Divide the total area costs by the estimated yield (e.g. 20 t FW/ha) £491/20 t fresh weight (FW) = £24.55/t FW = 2.5p/kg FW.

Convert costs of FW into DM variable costs = cost/kg FW x (100/DM%) So @ 25% DM = 2.5 x (100/25) = 10p/kg DM.

Compare the cost of silage to other feeds available to buy or sell, convert the costs of a kg DM into pence of mega joules of metabolisable energy (MJ ME) So grass silage at 11 MJ of ME/kg DM = 10/11 = 0.91p/MJ of ME.

To order a hard copy of any of the following, please contact publications@ahdb.org.uk or call 0247 799 0069:

• Livestock and the arable rotation
• Planning grazing strategies for Better Returns
• Improving pasture for Better Returns