Reducing chemical nitrogen (N) fertiliser use without reducing grass growth will help reduce costs, reduce surplus N available for loss and decrease the potential for nitrous oxide emissions. In 2022, chemical N fertiliser use in Ireland fell to 343,000t.

The four-year average chemical N fertiliser use from 2018 to 2021 was 373,000t/year. A major focus of this open day will be the area of improved N fertiliser management.

The N supply in pasture-based production systems comes from three sources: soil (through N mineralisation), white clover (through biological N fixation) and chemical N fertiliser application.

By optimising soil N mineralisation, incorporating clover into grass swards and refining chemical N fertiliser input, the total amount of N supply available to a sward can range between 450 and 500kg N/ha. All three N sources work in tandem and influence one another.

Reducing nitrogen use while not reducing grass growth is a key objective. \ Donal O'Leary

It is not practical to depend solely on traditional calendar-focused dates to apply chemical N fertiliser. In recent years, weather patterns in spring, summer and autumn have all been very variable, with no two consecutive years following similar patterns for rainfall and daily temperatures.

Precision N management

Nitrogen management during the grazing season needs to be better refined to achieve a greater response to both organic and chemical N applications and reduce the risks of N loss. The concept of precision N management is relatively new in grazing management practise. Precision N management (using grass growth predictions and grass measurement) is a key tool to optimise grass production and minimise N loss. This is now easier to implement using grassland data from PastureBase Ireland, weekly MoSt grass growth predictions and Met Éireann weather information.

During the open day, farmers will see how grass-clover swards with approximately 20% clover content can produce between 12.5t and 14.5t DM/ha with 150-200kg chemical N/ha.

A key challenge is to increase this DM production level further. We are now in the age of reduced chemical N fertiliser use, which means the incorporation of grazing and conservation legumes (white and red clover) into swards needs to be completed seamlessly.