Recent wet weather across Northern Ireland has resulted in grass swards being ineffectively grazed, damaged or not harvested, which not only affects herd performance now but also winter forage diets.
This is according to the senior technologist at the College of Agriculture, Food and Rural Enterprise (CAFRE) in Greenmount, Judith McCord who has given advice on managing swards in unpredictable weather.
Northern Ireland saw more than double its average rainfall last month with 185.4mm, which is 207% of its long-term average, according to figures by the Met Office.
GrassCheck data shows that across Northern Ireland the average grass growth to the end of July 2023 at 7.06t of dry matter (DM)/ha was down by 11.4%, compared to the long-term average of 7.97t DM/ha.
Current metabolisable energy (ME) and crude protein (CP) are similar compared to previous years, however, the DM percentage has consistently been lower than normal throughout most of July, according to the CAFRE.
Grazing during wet weather
The CAFRE senior technologist said that wetter silage and lower grazed grass quality will reduce DM and energy intakes, and therefore diets will have to be adjusted.
“There is variation in grazing and cutting scenarios across the province with some second cut silages cleared up in the last couple of weeks, and some multi-cut systems having a third cut in.
Although these have been mostly “snatch and grab”, the desire for high ME silage and efficient grazing may be subject to change for 2023 as farmers can only work with what they have, she said.
McCord advised that, where possible, heavier stock should be kept on drier soil conditions. Moving stock at least once daily will help to minimise poaching damage with the addition of more entrance/exit ways into paddocks, where possible.
Sward assessment is more crucial than ever with dry matter intake (DMI) reduced in wetter conditions. DMI should be kept consistent with the ability to buffer feed silage at milking times and pre-grazing grass covers kept at no more than 3,000kg DM, she said.
On-off grazing should be considered as animals are capable of eating all their daily requirements for grass in two, three-hour sessions, McCord added.
Silage
Commenting that minimising compaction is a “major challenge”, and that it therefore is important to consider the harvesting process, McCord said:
“Make sure mowers are correctly set for the ground conditions, plan your mowing route to avoid wet patches and leave areas that are too wet to cut – this can potentially be baled later.
“If conditions remain difficult, consider mowing dry and grouping rather than tedding and raking. At this stage you want to avoid damaging ground and soil contamination.
“Where ground conditions are heavy, consider leaving and baling later when conditions improve. For the snatch and grab cuts, remember that silage additive may help in the fermentation process and advice should be sought beforehand.”
Where swards have been growing for eight weeks or more but conditions remain difficult to harvest, the advice is to not damage ground by trying to snatch and grab a cut, she said.
“The nutritional quality of these swards has already been substantially compromised and the delay in cutting each week accounts for 10% increase of dry matter yield, digestibility drops by 3.5% and ME reduces by 0.6 megajoule (MJ)/kg DM.
“It has to be reasoned that wet and nutritionally poorer quality silage will not be suitable for milk cows alone and preparing for a drier third cut may help in the winter rationing.
“Where possible split your cuts based on DM for easier accessibility come winter rationing,” she said.
Managing effluent
This year will see a larger volume of effluent due to heavier crops harvested in wetter conditions. Grass harvested at 18% DM will produce approximately 150L/t while, grass harvested at 25% DM will produce around 25L/t, she said.
“Before filling the silo, firstly inspect the walls and floor to ensure they are free from cracks, are impermeable and no effluent can escape and, if needs be, carry out any necessary repairs.
“Consider lining silo walls, particularly at joints to help seal the silo. Check silo channels are clear of debris to prevent overflows and effluent flow is direct to a suitable storage tank – do this on a regular basis once the pit is full.
“Given the current wet weather, wilting may not always be possible leaving an increased pollution risk from bales produced. Choose a suitable location to store silage bales,” she said.
If silage bales are stored on concrete, there must be run-off collection. If storing in a field, McCord advises to place them close to a track or lane to avoid compaction during winter months.
Repairing damage to swards
Where heavy covers have been tramped and there is extensive damage, there may be a requirement for full sward reseed.
McCord highlighted that farmers should plan to address any compaction issues by sub soiling or ploughing when soils dry out.
“Where larger areas are to be repaired, a similar seed mixture to the original should be stitched in using a suitable machine,” the CAFRE senior technologist said.
For DIY repair, the area should be chain harrowed and a similar seed mixture to the original should be broadcast and then rolled.
However, advice should be sought beforehand, she said, along with a nutrient management plan on fertiliser and slurry application.
It is reasonable to expect to have to reseed 10-20% of the farm per year to achieve the farm’s full grass growth potential. However, she said, with a year of potential damage this may prove to be more.
For farmers who have effectively cut silage ground, applying slurry for the successive cut is next. “Typically for every kilogram of nitrogen applied (from bag/slurry) you can see a 25kg DM response.
“Nitrogen in slurry is prone to volatilisation losses, so [it] should ideally be spread on a dull, drizzly day but not when heavy rain is falling or expected,” she added.
