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Reseeding is one of the safest investments in farming, yet every year, just 5% of Northern Ireland (NI) grassland is sown out in new swards, farmers heard at an industry webinar last week.
The event, organised by Kilwaughter Lime, saw speakers cover the basics of reseeding from addressing soil fertility to managing a new sward post-emergence.
In the opening address, Richard Moore from Thompsons Feeding Innovations said grass is a crop and therefore, sward rejuvenation should be part of the crop’s management.
“At current prices, a full reseed from the initial spraying off to post-emergence will cost between £400 and £450/ac,” said Moore.
He pointed to research from Teagasc which shows new swards with 100% ryegrass content increase nitrogen utilisation by 24% when compared to older swards, and deliver an extra 3t DM/ha in yields.
“This equates to an extra six bales/ac every year, or two trailer loads of grass ensiled. At a cost of £200/t dry matter, the economics mean a reseed is paid for in two years.
“Silage quality will also be higher and as D-Value increases, purchased feed use can be reduced,” outlined Moore to the audience.
He concluded that the annual rate of loss in ryegrass swards is typically 10% to 15%, meaning farmers should be renewing swards every seven years.
Lime
Healthy soils are built on three principles according to Kevin Havekes of Kilwaughter Lime.
First off is drainage and soil aeration, as water-logged or compacted soils inhibit soil bacteria, thereby limiting crop yields.
Next is soil acidity, with mineral soils needing a pH 6.3 to 5.6 and finally, macro-nutrients should also be kept in mind.
“A soil at pH 6 is not good enough. There is still 11% of nitrogen and 48% of phosphorous locked up. If we applied 27-4-4 at a conservative cost of £600/t to soils at pH 6, there is £90 of nutrients locked up that plants cannot access.
“At pH 5.5, this figure increases to £150,” said Havekas.
Addressing soil PH
Liming soils when reseeding is vital. Grass seedlings have limited energy reserves. Having soils at the correct pH releases phosphorous to develop plant roots.
“All limes are not equal, so it is important to choose the right type of lime and ensure the correct application rate to get the best results possible,” said Havekes.
“Lime is measured on neutralising value and the size of particles. The smaller the liming particles, the faster they condition the soil.
“Conventional ground lime is best used when soil pH is below 5.5 and ploughed in. But the downside with ground limestone is 50% of particles are greater than 0.5mm and 30% greater than 1mm in size.
“These particles can take six to 18 months to break down and give the full lift in soil pH.
“A compromise to get new grass established is to apply 1.5t/ac of ground limestone, prepare the seedbed, then apply 100kg to 150kg/ac of granulated lime to give an instant neutralising effect.
Always use granulated when stitching in grass seed
“For soils at pH 5.7 and above, granulated lime works best as it gives the full lift inside six weeks. Apply 50kg/ac of granulated lime for every 0.1 increase in soil pH required.”
The advice is to always use granulated when stitching in grass seed. Ground lime sits on the soil surface, raising the top 1cm above soil pH 7 and causing nutrient uptake problems.
While granulated lime gives a longer-term neutralising effect of three to five years, Havekas said that once soil pH has been corrected, applying 100kg/ac of granulated lime every spring maintains soil pH.
Costed out over a 20-year period, there is a £40/ac saving with granulated lime due to the faster neutralising effect.
Fertiliser
There is no point reseeding grass unless soil fertility is corrected beforehand, Tony McIvor from Gouldings told the audience.
The advice on conventional reseeding was shallow ploughing, as essential nutrients, particularly phosphorous, lie in the top 2cm of the soil.
“Feeding the soil is important. Nutrients applied must be incorporated in the seedbed, not sitting on the surface.
“On mineral soils at the index 2 for P and K, apply 50kg/ha (40 units/ac) of P and 60kg (48units/ac) of potash.
“It is important to select a fertiliser commonly used for tillage when reseeding. Most grassland products do not have enough P and K,” said McIvor.
Grass varieties
Last up, David Linton from Barenbrug said 80% of NI swards are perennial ryegrass based. While the focus is currently on the benefits of multi-species swards (MSS), Linton said they do not have to include herbs, but a range of grasses.
“For the majority of NI livestock farms, go for two-thirds diploids and one-third tetraploids to cover all bases on soil type, weather, growth at the shoulders of the years and tillering ability,” said Linton.
“Choose heading dates based on when you intend to cut silage. But be mindful that if you need grass for early grazing, do not select all late heading varieties as they are slower to grow in spring.”
Advances in plant breeding mean other grasses such as timothy, fescue and cocksfoot have a role in modern grazing systems.
With clover, there will be peaks and troughs in growth, so it needs to be mixed with other grasses to provide even growth
“Grass breeding has moved with the times. Cocksfoot is a great deep rooting plant with aggressive growth in the spring and autumn.
“Modern cocksfoot are softer grasses with high palatability that are more tolerant of wet conditions.
“Tall fescue is similar and can grow to a root depth of 1m deep, tapping into soil moisture and nutrients that ryegrass cannot get near. It also has 9% higher protein and stock love it.
“Even when it heads out, new varieties of tall fescue will hold its feed value for longer than ryegrass.
“With clover, there will be peaks and troughs in growth, so it needs to be mixed with other grasses to provide even growth over the year.”
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