Milder winters are affecting grass growth and forcing dairy producers and advisers to reconsider their grassland management at the end and beginning of the grazing season.
Over the past couple of years the number of farmers who have either struggled to achieve a complete end of season rotation—or have been worried about the quality of grass to turn milking cows into—has been noted by the LIC consulting team across the country.
“The amount of grass growth through winter has been the main the cause of this,” says LIC Pasture to Profit consultant, Sean Chubb. “It has led us to question if is it time to rethink the target we have for the start of our last rotation and the closing covers.”
Most autumn grazing plans are setup from historic winter growth rates. This assumes no growth in December and January, as the decline in light hours reduces the solar energy grass can capture and soil temperatures drop below 5 deg C, resulting in the grass stopping growing. This dormancy is then broken in February when cows are turned out and their grazing stimulates the grass to grow.
Air temperature and growth
“Two factors are seeing this historical narrative change,” he maintains. “The first is that the average winter temperature has been increasing as can be seen in the graph. The other factor is the use of hybrid grasses which have higher growth rates at the beginning and end of the season.”
Having a high mean air temperature won’t always translate into more grass growth. There needs to be six days of soil temperature at 10cm above 5 deg C for grass to start growing, notes Mr Chubb. So one frost a week could be all that’s needed to keep grass in a dormant state.
“To see how soil temperatures are tracking through winter, regular readings were taken at Walford College in the midlands last winter (see table). As the winter has been mild with few frosts, we have seen soil temperatures remain above five degrees C well into January and as a result the grass kept growing. While the average temperature for the farm was still below five degrees at the end of January, around half of the farm was at 5.0 to 5.1 degrees.
“With a shorter period when growth stops, grassland management in the autumn and closing covers is critical for carrying high quality grass through the winter or carrying the correct covers for a farm’s calving spread.
“Even if grass growth continues throughout the winter in the future, this will not see much movement forward as the sunshine hours will be the limiting factor,” says Mr Chubb.
So what are the potential grassland management changes that are needed if this level of winter growth continues.
“For spring block farmers who are targeting grazing to the end of November or into December, this could mean that they should start the last rotation at a later date—say October 15th to 20th—instead of the 10th,” he suggests.
“This will result in the speeding up of the final round and potentially Sean Chubb says grazing specialists will have to review their future plans.
Change in mean UK winter air temperatures each decade since 1880 closing at a slightly lower cover than producers do now, but still achieving the desired opening cover.”
Out wintering option a consideration
Could out wintering some cows on grass and bales like in the North Island of New Zealand be the most cost-effective option? “For farmers that have heavy soils and a wet winter, this could mean grazing your yearling heifers through winter to maintain covers and quality,” suggests Mr Chubb.
“On autumn calving units do we need to target a second balance/magic day in the autumn just before we house the cows?” he asks. “Drop the average farm cover down to say 1,900kg DM by the end of October if there is going to be 400kg DM of growth through November, December and January. This may allow turnout in early February with an average cover of 2,300kg DM.”
If the soil conditions allow, can we turn out earlier? “If we were to start our spring rotation in the middle of January, with a flat wedge from a fast closing round, maybe we could achieve close to 50% grazed by the end of February without running to a feed shortage towards the end of the first round.
“The biggest question I see is what we should do with silage paddocks. Especially the silage paddocks that are on off lying land, as it’s easy to incorporate silage paddocks into the grazing rotation if they’re on the edge of the milking platform.
“If weather dictates that the last cut is being taken in September, and the first cut is taken in April, are we going to start seeing the quality of first cut reduce and regrowth slow from having too high covers? The obvious solution is going to be grazing these paddocks with one class of stock or another in October or November. But this can be difficult in some cases as it could mean the need to move stock between multiple blocks.
“The use of Nitrogen and slurry in the back end of the season is the other tool we have to control the level of growth in the autumn and winter. This could mean reducing the amount of Nitrogen applications in the autumn to allow for slurry stores to be emptied going into the winter without boosting growth above what is needed,” comments Mr Chubb.
Reviewing grass growth during winter
While measurements are showing an upward trend in winter temperatures, this is just one aspect that impacts on the growth rates. Therefore, reviewing the level of grass growth through the winter is required to see whether adjustment is needed, as the shoulder periods are the most expensive for producing milk while grazing.
“If the warmer winters allow us to change our management slightly and result in the reduction of the amount of concentrates or silage used through this time frame, we will be lowering the cost of production and building a more resilient business at the same time,” he concludes.