Sward diversification should not be overlooked, as farmers have to consider all options in order to minimise their fertiliser requirements.
With the introduction of the National Fertiliser Database, the cost of fertiliser, the problems highlighted with water quality and the push to secure a nitrates derogation for dairy farmers, all options must be explored to reduce your fertiliser usage.
Diversification of the plant species in swards can be more effective than the application of microbial inoculants in supporting productivity in intensively managed grasslands.
This is according to a new scientific paper from Teagasc, UCC and international collaborators and was led by researchers at the Teagasc Environment Research Centre, Johnstown Castle, Co. Wexford.
The study concludes that integrating legumes and herbs into intensively managed swards is more effective for maintaining or enhancing nutrient uptake and herbage yield than applying the evaluated microbial inoculants to seed at sowing.
To reduce fertiliser input requirements and maintain grassland yield, farmers are considering options such as diversifying grassland sward composition by introducing a variety of plant species and functional groups.
Another way to reduce your fertiliser reliance is by applying microbial inoculants that have the potential to promote plant health.
However, the relative effects of both management options have been rarely tested in grasslands.
Sward diversification
Senior research officer with Teagasc at Johnstown Castle, Dr. Fiona Brennan stated that “using a two-year grassland field trial we tested the efficacy of eight microbial inoculant treatments”.
This was tested with bacterial and arbuscular mycorrhizal fungal (AMF) inoculants applied singly or in a combination.
“Each of these eight microbial inoculants were applied to seed or the seedbed of three types of grassland swards comprised of grass only, grass-clover or a six-species mixture of grass, clover and herbs,” Brennan added.
All three types of grassland swards then received 100kg/ha/year of nitrogen (N) in the form of protected urea.
UCC lecturer and former postdoctoral researcher with Teagasc, Dr. Israel Ikoyi outlined the main findings:
“Our study found that in both years, mixed swards [grass-legume and grass-legume-herb swards] significantly increased nutrient uptake and yield compared to grass-only swards,” he said.
Ikoyi found that the microbial inoculants that were evaluated had no significant effect on yield.
On the other hand, switching from grass-only to grass-legume or grass-legume-herb swards increased yields by 3932kg/ha per year and 4693kg/ha per year, respectively.
These increases in yield from the more diverse swards indicate potential fertiliser nitrogen (N) savings of 97 to 117 kg/ha per year, representing a substantial reduction in fertiliser costs for farmers.
Head of the Teagasc Environment Research department, Dr. Karen Daly said:
“Dr. Brennan’s team have demonstrated the importance of having robust scientific evidence to help farmers make the right decisions for managing grasslands sustainably.”
Overall, under controlled field plot conditions, including legumes and herbs in a grass sward proved to be a far better farm-scale management strategy for increasing grassland forage yield and nutrient uptake than the application of microbial inoculants.