Zero grazing under scrutiny in nitrates review

Teagasc says it helps farmers with fragmented land but brings risk of increased nitrogen surplus and loss

Zero grazing is a practice being adopted more and more at farm level, and a review on best practice for grazing and nutrient management will be undertaken as part of the ongoing review of Ireland’s Nitrates Action Programme.

In its submission to the review, Teagasc addresses considerations for the incorporation of zero grazing in farming systems.

The increased prevalence of zero grazing on intensive farms is acknowledged.

The practice of zero-grazing has allowed farmers on fragmented land holdings to greatly increase the utilisation of outside land blocks to provide high quality home grown feed to maintain animal performance in spring and autumn, when grass-growth rates are low relative to animal feed requirements.

Zero grazing also provides for a more even redistribution of recycled slurries on grassland across fragmented land holdings, and reduces the risks of nitrogen losses from urine patches on free draining soils, particularly during the autumn.

However, it is generally associated with increased stocking rate on the milking platform, which has the potential to create nutrient loss hotspots, as these milking platforms are operated at very high stocking rates.

Increasing the amount of manure generated through reduction in grazed grass could potentially increase ammonia emissions, and this needs to be considered, when reviewing the potential of zero grazing.

As a widespread mitigation practice for nitrogen loss, the potential of this approach to Irish grazing systems must also be considered in terms of the additional economic costs associated with substantially increased mechanical handling of both feed and slurries, when compared to grazing in situ.

From an economic perspective, researchers Dillon et al (2008) reported a strong positive relationship between the amount of grazed pasture in the diet of the dairy herd and milk production costs, while the full economic costs of zero grazing are similar to the costs of grass silage conservation (Finneran et al, 2012).

Moreover, an increased reliance on zero-grazing will also require increased slurry storage, and on-farm mechanisation, both resulting in significant cost increases, in addition to increased ammonia emissions.

In cases where slurries are not recycled evenly across the entire land area, the practice of zero-grazing can result in increased nitrogen surpluses and losses on the main grazing platform.

At the same time, the further confinement of animals for zero-grazing will also result in a reduction in grazing season length on farms, which is an area of increasing animal welfare concerns for the European dairy industry.