Sward diversification more effective for higher yields than some microbial fertilisers

A new scientific paper from Teagasc, UCC and international collaborators has shown diversification of the plant species in swards can be more effective than the application of microbial inoculants in supporting productivity in intensively managed grasslands.

"Dr Brennan’s team have demonstrated the importance of having robust scientific evidence to help farmers make the right decisions for managing grasslands sustainably.”

The paper led by researchers at the Teagasc Environment Research Centre, Johnstown Castle, Wexford has just been published in the respected journal, Plant and Soil. 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 (often called bioinoculants) 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, as well as 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.

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 (with bacterial and arbuscular mycorrhizal fungal (AMF) inoculants applied singly or in 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 6-species mixture of grass, clover and herbs, and received 100 kilograms per hectare per year of nitrogen 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. The microbial inoculants evaluated had no significant effect on yield, while switching from grass-only to grass-legume or grass-legume-herb swards increased yields by 3932 kilograms per hectare per year and 4693 kilograms per hectare per year, respectively.

These increases in yield from the more diverse swards indicate potential fertiliser N savings of 97-117 kg/ha/yr 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.”

The published scientific paper titled ‘Manipulation of sward diversity is a more effective management strategy than addition of microbial inoculants in intensively managed grassland’ can be viewed at https://link.springer.com/article/10.1007/s11104-024-06849-7 .

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.

This work was carried out as part of the ‘Microbiome applications for sustainable food systems through technologies and enterprise’ (MASTER) project led by Professor Paul Cotter, Teagasc  https://www.master-h2020.eu/ and was funded by the EU Horizon Research and Innovation programme (grant agreement No. 818368).