Many farmers are asking themselves the same question this year: how can they increase production using less inputs such as nitrogen fertiliser than previously?
The cost-benefit of reseeding grassland
Germinal technical manager Dr Mary McEvoy explains the cost-benefit analysis behind reseeding grassland.
“Budgets are stretched this year so you’ll want to make every last cent count,” says Dr McEvoy. “Fertiliser must be well targeted and it’s worth thinking carefully about reseeding under-performing swards as a cost-effective alternative to drive production.”
Dr McEvoy adds, “Swards with a higher percentage of perennial ryegrass give a better response to nitrogen so are more efficient per unit of applied fertiliser. They also produce more dry matter.”
Effect of sward perennial ryegrass content (PRG) on DM production
| Sward PRG Proportion | 15% | 25% | 40% | 65% | 100% |
| Spring Yield (kg DM/ha) | 364 | 447 | 538 | 822 | 910 |
| Summer Yield (kg DM/ha) | 5,832 | 6,424 | 6,457 | 6,852 | 7,414 |
| Autumn DM Yield (kg DM/ha) | 3,958 | 3,903 | 4,212 | 4,269 | 4,036 |
| Total DM Yield (kg DM/ha) | 10,154 | 10,774 | 11,206 | 11,943 | 12,360 |
Source: P Creighton et al., 2010
“Typically, the advice is to reseed 10-15% of pasture each year to keep production levels up,” says Dr McEvoy. “However, this year it isn’t that simple. There is a careful weighing up which needs to be done.
“On one hand, with budgets tightened, reseeding may seem an unnecessary expense. On the other hand, an old sward doesn’t perform as well and applied nitrogen isn’t used as effectively so you’d need to use more to keep production levels up.”
Sward assessment
To make the best decisions about reseeding grassland, assess the performance of your existing swards. Walk the farm weekly, reviewing each paddock individually as well as the whole system.
Take note of the following which all indicate an under-performing sward:
- High weed burden (docks, thistles)
- Severe poaching or damaged ground
- High levels of unproductive grass (e.g. meadow grass/bentgrasses)
- Slow regrowth and recovery in rotations
- Poor nitrogen response
- Drop in milk yield
Increase grass production by reseeding with modern varieties
Once decisions are made regarding which fields to reseed, it’s important to choose the right grass varieties to suit your farming system.
“I always refer farmers to the Pasture Profit Index (PPI),” says Dr McEvoy. “The varieties on the list have been through a rigorous testing regime and assessed for their suitability for the conditions on Irish farms.
"It not only gives an economic value to each of the listed varieties but highlights their strengths and weaknesses so you can analyse its suitability to meet your system’s requirements as well as its return on investment.”
Varieties listed on the PPI are at the cutting edge of grass seed development with Germinal varieties rated highly across all categories year after year.
In 2022’s list, Germinal varieties secure the top two spots in all four categories, with AberBann and Barwave new to this year’s listings.
How to reduce nitrogen fertiliser use
“If reducing the use of nitrogen fertiliser is at the front of your mind, I’d also look at adding legumes to your mix, such as red and white clover – not only will they fix nitrogen in the soil, but they offer valuable protein and energy too,” adds Dr McEvoy.
“When looking at whether to keep an existing sward for another year or to reseed, remember by reseeding you’re not replacing like for like, you’re replacing with better.
"Seed genetics are improving every year and each new variety provides better performance. Use the latest plant genetics to drive grass production, rather than fertiliser.”
Dr Mary McEvoy discusses reseeding benefits with Irish farmers
For more videos and guides on reseeding, visit our Germinal Knowledge Hub.
This article is the first in a series on grassland reseeding. Next time, we will share the best techniques for reseeding pasture. If you have any questions, please ask our grass and forage seed experts.