Work

Transitioning to low chemical nitrogen perennial ryegrass white clover pastures on wetland grazing dairy systems

Year: 2025

Type: article

Abstract: Context Reductions in chemical nitrogen fertiliser applications in agricultural systems within the European Union will have a significant role in reducing greenhouse gas emissions related to agriculture. Aims The current study investigates the transition from old permanent perennial ryegrass (PR) swards (PR-old) to newly established PR (PR-new) receiving high levels of chemical nitrogen (N) application or PR white clover swards (PRWC) receiving lower levels of chemical N application on wetland soils in the border, midland and western region of Ireland over 3 years (2021–2023, inclusive). Methods The experimental site, which consisted of old PR swards, was transitioned to either new PR swards receiving up to 250 kg N/ha per annum or PRWC swards receiving up to 125 kg N/ha annually. Key results In the year of establishment, PR-new and PRWC-new swards has a significantly reduced total pasture DM yield (8925 and 8561 kg DM/ha) compared to older PR swards (14,182 kg DM/ha) while PRWC oversown (PRWC-over) swards were intermediate (11,330 kg DM/ha). In subsequent years, PR-new, PRWC-new and PRWC-over swards achieved increased DM yield (14,891, 15,642 and 15,218 kg DM/ha) compared to older swards. Within PRWC, white clover contents increased from 0 g/kg DM in early 2021 to 250 and 190 g/kg DM in 2022 and 2023, respectively. Consequently, significant reductions in chemical N fertiliser applications were achieved, from 229 and 200 kg N/ha for PR-old and PR-new swards, respectively, and 124 and 84 kg N/ha for PRWC-over and PRWC-new swards, respectively. The PRWC system tended (P < 0.08) to have increased milk and milk fat plus protein yield (5197 and 473 kg/cow, respectively) compared to the PR (5092 and 461 kg/cow, respectively) during the 3 year study period. Conclusion These results highlight the potential for PRWC systems to increase pasture production and milk production, while reducing chemical N applications in comparison to PR only systems on a wetland soil. Implications The extent of sward renewal and initial reduction in pasture production may result in shortages in winter feed production during the transition to low chemical N PRWC systems.

Source: Animal Production Science

DOI: 10.1071/an24284

Authors: H. Walsh, D. Patton, J. J. Collins, L. Delaby, K. Pierce, B. Horan