Multi species swards: grazing trial at Johnstown Castle

Sub-title: Despite lower fertiliser nitrogen, dairy cattle on multi-species swards performed similarly to a herd on grass-clover

Aidan Lawless (Johnstown Castle), Mike Dineen (Moorepark), David Wall (Johnstown Castle) and John Finn (Johnstown Castle)

Introduction

Multi-species swards have shown several agronomic and environmental benefits in plot trials. To test multi-species swards in a grazed grassland system, a grazing trial with two high-EBI spring-calved dairy herds is ongoing at Teagasc, Johnstown Castle. One herd of 20 cows is grazing exclusively multi-species swards (MS), with our control herd of 20 cows grazing grass clover swards (GC). We are now well into our third full year of this grazing study, with two full years of results.

Sward establishment

During 2019, five fields of multi-species swards were established totalling 7.5 ha, all swards were fully sprayed off and reseeded with a six-species mixture with two grasses, red and white clover, chicory and plantain. The multi-species mix was decided based on previous plot trials at Johnstown Castle.  Both multi-species (MS) and grass-clover (GC) fields were reseeded over the course of the season from early May with the latest in early September, using both the conventional plough-till –sow method & also direct drilling into the sprayed off sward with no soil disturbance. Both methods proved successful.

Nitrogen and grazing management

A target application rate of ~ 100kgs/N/ha was planned for the MS swards in our first full grazing season post establishment, with 70% of this frontloaded as spring N applications. In both 2020 and 2021, at no stage after April did the MS sward look to be deficient in N (confirmed by high protein content of the grazing forage >18%). This resulted in no fertiliser N being applied for the remainder of 2021, with just an average of 65kg N per ha in 2021 (Table 1). In 2021, we reduced the N application to promote clover content - our current target on the GC swards is 120-140 kg N per ha by increasing clover content to ~20%.

Grazing management was similar for both herds. Cows were turned out to grass in early February straight after calving (weather permitting). Opening farm cover for the MS herd has been significantly lower (by 150 kg per ha of dry matter) in our three grazing seasons, resulting in about seven less grazing days for the MS herd during the first round in 2022.

No difference in herd performance

Overall annual performance of the herds across 2021 and 2022 has been remarkably similar (Table 1). Both herds produced identical milk solids at 537 kg per cow.

Forage yields/silage production

Both herds had very similar yields of grazed forage (Table 1). Lower overall production of the MS swards resulted in lower silage production with 1 tonne per cow of dry matter being conserved versus 1.4 tonne per cow of dry matter on the GC herd. Silage quality has been very good on the MS swards, with typical first cut silage at 74% DMD and 30% DM. When making multi-species silage, cut when the crop is dry and allow to wilt for minimum of 24-36 hours before conserving. 

Long-term trial for agronomic, livestock and environmental performance

Results to date have been very promising, and the reduction in fertiliser N inputs on the MS swards are very significant. It is envisaged that this systems trial will run for a further five years in order to answer some key questions. These include sward persistency and changes to sward composition over time, cow health and production, long-term annual forage production, methods to rejuvenate the sward (if needed), benefits of more diverse swards for the soil structure, greenhouse gas emissions, water quality, soil carbon sequestration, and biodiversity effects.

Table 1. Annual performance averaged across 2020 and 2021.