Reseeding can improve the productivity of a sward; however, for it to have maximum effect soil fertility must be correct, according to Teagasc.
It says getting soil fertility right is crucial if perennial ryegrass is to establish well and persist after reseeding.
Soil sample fields in advance of reseeding – where establishing grass seeds by ploughing take the soil sample from the ploughed soil to get a better indication of the soils fertility status and future fertiliser applications.
Establish soil P & K levels and apply suitable fertilisers/manures before or during soil cultivations. Check soil pH and apply lime as recommended on the soil test report.
Reseeding time offers a perfect opportunity to correct soil pH and apply lime. Apply lime to the seedbed and incorporate into the top 10cm of soil. This will provide the ideal conditions for fast and even seed establishment.
Where soil magnesium levels are low (<50pppm) apply magnesium limestone to correct soil Mg levels.
Phosphorus (P) & Potassium (K)
Soil P and K are an essential at reseeding time. P and K are required for rapid root and tiller development during the early stages of establishment. In addition P & K is required to ensure the longevity of rye grasses in the sward over time.
Aim to maintain soils at Soil Index 3 for maximum production and persistency of clovers and rye grasses. Apply P & K fertiliser as per soil test report and incorporate into the seedbed at sowing time (see table below).
Insufficient soil P & K will result in poor establishment of rye grasses / clovers and the benefits of reseeding will be lost.
Additional P allowance of 15kg P/ha is available at index 1, 2 & 3 for reseeds as per Nitrates.
Suitable fertilisers include 0-10-20, 10-10-20, 0-7-30 etc
Sufficient N is one of the essentials in aiding good grass establishment. Grass seeds have a low N requirement during the early stages of establishment. Too much N will encourage weed growth and competition for new grass seedlings.
Apply approximately 40-75kg N/ha at sowing time to maximize grass growth. Apply 30 to 40kg N/ha four to six weeks after reseeding.
Undersown crops apply 40kgN/ha after cereal harvest. Reseeds following long-term tillage will benefit from additional N in the first five years after reseeding.
Organic Manure–Good Source of N, P & K
Apply organic manures/slurries to build soil fertility status while supplying nutrient requirements. It is best to rapidly incorporate high N manures (pig / poultry manures) to reduce N losses (N).
When applying organic manures to P index 1 & 2 soils only supply 50% of crop P requirement in organic form and the remaining 50% as chemical P.
Make sure that manures are applied evenly and well incorporated at sowing time. This will reduce problems during establishment especially in a min-till system.
Mark Plunkett, Teagasc, Johnstown Castle, Research Center,