An annual reseeding programme should be part and parcel of grassland management. It does not have to be a big area that is reseeded each year. Instead, the little and often approach is a much better option as it is cheaper and it is easier to manage. Just like in cattle breeding when you change your stock bull for a young bull with new bloodlines that will deliver faster growing calves, reseeding will introduce newer varieties of perennial ryegrass that can yield more grass from similar levels of inputs.

But before you decide to reseed an underperforming paddock, there are a few things to be considered. Simply ploughing a field and sowing out again will not guarantee a successful reseed that can double your grass growth. Instead, doing a bit of preparation planning will increase the chance of the new sward performing over a prolonged period of 10 to 15 years.

1 . Soil fertility: always soil sample any field you are planning to reseed. There is no point in reseeding a paddock that is underperforming unless you identify the cause of the problem. Soil analysis on grassland farms shows that 90% of soils are below the optimum P and K levels and 70% of farms need lime.

When it comes to soil fertility, a field that is highly acidic or is lacking in soil nutrients will struggle to support high grass growth, even when reseeded without any change in management. For grassland, soil pH levels should be around 6.0 to 6.5. Below this level, soil nutrients become locked up. At soil pH 5.5, approximately 50% of the nitrogen you apply from bagged fertiliser is available for grass growth. At the same pH level, around 33% of P and 50% of K applied is available. That means every bag of CAN applied will only be supplying 13 units/acre, instead of the 27 units/acre actually applied.

At a fertiliser price of €240/t for CAN, every bag (50kg) is costing €12. On a farm that spreads five bags of fertiliser per acre on grazing ground over a growing season, it will have wasted €30/acre from the lack of nitrogen availability due to low soil pH. The same €30/acre would pay for around 1.5t/acre of lime to be applied, which would greatly increase soil pH and nitrogen availability.

2 . Is the soil compacted? Soil compaction will limit grass growth as it prevents grass roots from penetrating through the sub-soil and tapping into nutrients. Compacted soils also hold surface water, which keeps soil temperatures lower in spring and autumn, therefore reducing grass growth in the early and late season. Also, as compacted soils hold the plant roots close to the soil surface, they can be damaged from poaching during wet periods. This inhibits growth and slows recovery compared with swards with deeper penetrating roots. Before reseeding, dig a few random test holes in the field to see if there is any compaction. If there is no compaction, you will not necessarily have to plough the field to reseed it. Min-tilling may be an option instead, which can possibly reduce costs and bring the field back into the grazing rotation faster. If there is a compaction problem, can it be cured from sub-soiling or will it require ploughing?

3. Drainage: is there a drainage problem in the field that needs to be addressed? Reseeding presents a good opportunity to get drainage sorted but it adds to the cost. Plastic drainage pipe and stoning is the best option, but it is also more expensive.

In some fields with a high clay content, gravel tunnels and mole drains can cut down the drainage cost and be used to link into piped drains. How long will mole drains last? In clay soils, mole drains should hold for a number of years, but in silt soils, they will collapse. To test how suitable the soil is for mole ploughing, take a handful of clay from a depth of 15 to 18 inches. Roll it into a ball and leave for 24 hours in a bucket of water. If the clay ball holds its shape, it will hold a mole drain. If it has not held its shape, the mole drain will not provide an effective draining solution.

4. Burning off the old sward: burning off the old sward will prevent the regrowth of older grass and weeds, giving the new grass seed a better chance to establish. However, make sure to graze off the old sward before ploughing or direct-drilling new grass seed. This reduces the amount of trash to be buried by the plough and improves the soil surface contact when min-tilling grass seed. If using a min-til method for reseeding, the older dead sward can be acidic which inhibits the new seed germinating, so applying lime before reseeding is a good idea. One tonne per acre of lime should suffice.

5 . Reseeding method: what reseeding option is best for your farm? For some farms on light stoney soils, min-tilling is the only option.

On heavy farms, ploughing is a better option, but it may mean that the field is out of production for a longer time. In a wet year, the ploughed field may be too soft to be grazed for the rest of the year.

There are various min-tilling methods and because the soil surface is not disturbed, they can support grazing if you are running tight for grass. However, the grass seedling has to be properly established and only use light weanlings or sheep to graze the reseed and limit to a couple of days before removing animals from the new sward. Some min-tilling methods can cut out, or combine tasks which will reduce the cost of reseeding.

By following some of the earlier steps, you will be better placed to decide which reseeding method is best for your farm.

6. Ploughing: ploughing will improve drainage and opens up soils that were compacted. If you are routinely ploughing ground between arable and grass rotations, ploughing to reseed is a good option as you are regularly turning soils. However, if you rarely reseed your farm, remember that when you plough down an old sward, you are also ploughing down the good soil with it. As a result, you may be bringing up poor quality soil with low organic matter to the soil surface. This soil may be lower in soil nutrients and therefore require more P and K to be applied.

7. Time to reseed: when is the best time to reseed? For some, spring reseeding works best as they struggle to get an August reseed sown out, post-emergence spray applied and grazed before weather conditions turn against them. In contrast, some farmers who are heavily stocked cannot afford to take a field out of the grazing rotation in the spring.

Some farmers operating on heavier land will also struggle to get on to the ground for a spring reseed. July and August provide a better option for many farmers, but it is important that regardless of when you reseed, you follow best practice. This includes using a post-emergence spray to control any weeds and getting at least one grazing to encourage tillering.

8. Selecting the right grass seed: will the new sward be used for grazing, silage or a mix of both? Can clover be included in the sward to fix soil nitrogen? Selecting the right type of grass seed to suit the field’s purpose is important and will increase the longevity of the sward.

9 . Controlling weeds: using a post-emergence spray shortly after the sward has become established will prevent weeds such as redshank and chickweed from getting into the sward and competing with new grass seedlings. Docks and thistles are also common weeds in a reseed. They are easier controlled at an earlier stage rather than waiting until they reach maturity, which is why is it is important to time reseeding so that you can get on to the field and spray before the autumn.

10 . Feed the reseed: young swards of ryegrass are highly productive if you regularly apply fertiliser. Without fertiliser, new swards can fail. Depending on soil fertility, you may need to be using compound NPK products. Farmyard manure will also increase soil organic matter which will condition the soil. It is also important to keep grazing the new sward regularly and ensure that animals graze tight to get the plant to tiller out fully.

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Focus: Reseeding and feed options