Effective reseeding and use of the Pasture Profit Index

Sarah Walsh Noirin McHugh Michael O'Donovan

Regular reseeding of pastures enables farmers to produce higher yields of better-quality grass, improving feed self-sufficiency and enhancing overall farm sustainability. It is recommended that 10% of the farm be reseeded annually. Current reseeding rates are estimated to be only 2% of the total grassland area. Although reseeding costs are substantial, currently estimated at €1,100/hectare (ha), the investment is typically recovered within 2-3 years due to the increased herbage yield achieved from reseeded swards. Permanent pasture with low perennial ryegrass content can cost farmers up to €450/ha per year due to reduced herbage production and low nitrogen use efficiency. Reseeding swards also has positive effects on animal performance through higher quality (e.g. digestibility) feed and increased utilisation.

Commercial farm research has shown that variety selection has a significant impact on herbage production and number of grazing rotations each year for up to 10 years post-sowing. For this reason, it is important to use the Pasture Profit Index (PPI), which is a perennial ryegrass selection index that identifies the most profitable varieties based on their performance differences.

Variety selection

The PPI should be used to select varieties when reseeding to ensure the best return on investment (Table 1). The data for the PPI is collected on five sites across Ireland by the Department of Agriculture Food and Marine to encompass the varying weather conditions and soil types across the country. The PPI outlines, in economic terms, the agronomic differences between varieties for traits that influence the profitability of ruminant production systems. These traits include spring, summer and autumn herbage production, herbage quality, silage yield, persistency and grazing utilisation. Each variety has a PPI value which is the sum of the traits and is the increase in profit/ha by sowing that variety.

The traits within the PPI facilitate system-specific variety selection. When choosing varieties for only intensively grazed paddocks (i.e. on the grazing platform), varieties performing well within the grazing utilisation, spring/autumn herbage production and quality should be used. Likewise, when choosing mixtures for regular silage harvesting, varieties which perform well in silage production, quality and spring herbage production traits should be prioritised. Research investigating mixtures of varieties found that the performance of a grass mixture for each trait is generally equal to the average performance of the individual varieties included in the mixture. Ploidy also influences traits, particularly grazing utilisation, with tetraploid varieties generally achieving higher grazing utilisation values. For this reason, it is recommended to use a minimum of a 60:40 mixture between tetraploids and diploids for grazing mixtures. Recent long-term commercial research reported similar persistence for diploid and tetraploid varieties sown in monocultures for up to 10-years post-sowing on 115 farms across Ireland.

 Updates to the Pasture Profit Index for 2026

The most notable update is the change to the ‘grazing utilisation’ trait from a star rating system to an economic value. The economic value is based on the grazing efficiency of a variety which is measured in Teagasc Moorepark. Varieties with higher scores in this trait consistently achieve lower post-grazing sward heights and can reduce the need for mechanical intervention (topping). The grazing utilisation trait is calculated across the 5 summer rotations using a value of €0.04/ kg dry matter (DM).

There was also a change to the economic value for persistency based on recent increases in the cost of reseeding, which is currently estimated at €1,100/ha. This equates to €92/ha per year across 12 years. All other economic values remain the same; however, there were some updates to the base values for seasonal and silage yield and quality. The base value for total annual yield is now 9.5 tonnes (t) DM/ha, which is proportionally split between spring, summer and autumn (1.059, 6.449 and 2.021 t DM/ha, respectively). The base value for first-cut and second-cut silage is 4.8 and 3.7 t DM/ha, respectively.

Reseeding program

The timing of reseeding is strongly influenced by weather conditions and grass supply on-farm. When swards are reseeded in spring, the total annual herbage production in the establishment year is similar to that of a non-reseeded pasture. White clover establishment is more reliable in spring as soil temperatures are rising. When reseeding is carried out in autumn, deteriorating soil conditions can make herbicide application and grazing more difficult, while lower soil temperatures can reduce germination rates.

• Soil sample for phosphorus (P), potassium (K) and pH.
• Spray off the old pasture with a minimum of 5 litres glyphosate/ha; allow a minimum of 7–10 days after spraying before cultivating.
• Prepare a fine, firm seedbed. There is little difference between cultivation and sowing

methods once completed correctly.

• Use grass varieties from the Pasture Profit Index or either of the Irish (Republic or Northern) Recommended Lists and white clover from the recommended list.
• Sow at a rate of 28–30 kg/ha of grass (max 3–4 varieties) plus 3.5–5.0 kg clover.
• Avoid sowing white clover seed too deep; sowing depth, approximately 10 mm.
• Roll well to ensure good contact between the seed and the soil.
• Apply a suitable post-emergence spray when weeds are at seedling stage.
• First graze at a pre-grazing yield of 800–1,000 kg DM/ha.

Post-sowing management

Docks and chickweed are two of the most critical weeds to control in new reseeds; it is important to control these weeds at the seedling stage, when they are approximately the size of a €2 coin, by applying the herbicide before the first grazing. When clover is included in the sward, clover-safe herbicide must be used. All pesticide users should comply with the regulations as outlined in the Sustainable Use Directive (SUD). New swards should be grazed as soon as the new grass plants roots are strong enough to withstand grazing (root stays anchored in the ground when pulled). The first grazing of reseeded swards should be completed at a pre-grazing yield between 800–1,000 kg DM/ha. Early grazing is important to allow light to the base of the plant to encourage tillering and white clover establishment. Frequent grazing of the reseeds at lower pre-grazing yields (<1,100 kg DM/ha) during the first-year post-establishment also has a beneficial effect on tillering and clover establishment. The aim is to produce a uniform, well-tillered, dense sward. If possible reseeded swards should not be closed for silage in their first year of production as the shading effect of heavy covers of grass will inhibit tillering of the grass plant and white clover establishment resulting in an open sward, which is susceptible to weed establishment.

Conclusion

Spring and early-summer are generally more suitable times for reseeding than autumn. Once a firm seedbed and good seed-to-soil contact are achieved, there is usually little difference between reseeding methods. However, the long-term success of a reseed depends heavily on post-sowing management, with grazing, weed control and fertiliser management all playing important roles. The PPI is a valuable tool for identifying the most suitable varieties for Irish farming systems, and understanding the strengths and weaknesses of individual varieties can help farmers make better reseeding decisions.

Table 1. Pasture Profit Index for 2026

Compiled and edited by Mark McGee and Paul Crosson, Teagasc, Grange Animal & Grassland Research and Innovation Centre, and first published in BEEF2026 – Driving Sustainable Performance, additional reading from BEEF2026 is available here.