Dairy and livestock farmers (slurry, fertiliser, lambing): the wind call, at your height

As a farmer, you make decisions daily that depend on the wind. When to spread slurry or fertiliser without it drifting onto a neighbour's land, or when to prepare for wind chill during lambing or calving, are calls you make often. These decisions are weather-gated, meaning you need specific conditions to proceed.

For slurry spreading, you have a limited number of suitable days within the spring and autumn windows. Missing these days can mean spreading in less ideal conditions later. During lambing, which can last for six to eight weeks, you assess wind chill daily to protect newborn lambs and calves.

Making the wrong call can lead to ammonia loss when spreading slurry on warm, windy days, which is less efficient and can have an environmental impact. For livestock, unexpected wind chill can affect the health of young animals. Your decisions are based on your experience and the specific conditions of your farm.

Your own document, such as your Nitrates Action Programme, sets the closed periods for spreading, but the day-to-day decision on wind conditions is yours.

Your work with slurry spreaders or tending to newborn livestock happens at ground level, typically around 2 metres high. Wind conditions at this height are what directly affect your operations. The instrument shows wind at 10, 80, 120, and 180 metres, and interpolates to your specific working height, such as 2 metres.

It is important to distinguish between mean wind speed and gusts. Gusts are short, sudden increases in wind speed that can cause slurry to drift unexpectedly or increase the felt wind chill for animals. The instrument displays gusts alongside the mean wind speed.

Your limit for wind speed, whether for spreading or for assessing wind chill, is set by your own farm judgement and experience. There is no legal wind limit for slurry spreading, so you determine what is acceptable based on your specific equipment and local conditions. For wind chill, your own experience with what affects your animals will guide your limit.

The instrument helps you apply your own limit to the forecast wind at your working height, providing a clear picture of the conditions where your work takes place.

The instrument shows the odds, P(above your limit), by the hour. This is the fraction of ensemble members that predict wind speeds above your set limit for that specific hour. It gives you a probabilistic view, rather than a single forecast.

For example, if the odds are 20 per cent that wind will be above your limit for slurry spreading, you might proceed with caution, knowing there is a low chance of exceeding your threshold. At 50 per cent, you would likely reconsider or delay the task, as the chances are even that conditions will be unsuitable. If the odds reach 80 per cent, it indicates a high likelihood of exceeding your limit, suggesting you should not spread slurry.

The Agreement Spine shows where different weather models agree or disagree on the forecast. If the Spine is thick, it means models are diverging, and the forecast has more uncertainty. A thin Spine indicates strong model agreement, which can give you more confidence in the forecast.

By understanding these odds and model agreement, you can make informed decisions about when to spread slurry or fertiliser, or when to take extra precautions for your livestock against wind chill.

This is an example of how you might use the instrument on a typical day:

• 06:00: You check the forecast. The instrument shows a 20 per cent chance of wind above your slurry spreading limit for the morning, rising to 60 per cent by midday. You decide to start spreading early.
• 08:30: You check again. The odds for the morning remain at 20 per cent, but the midday odds have increased to 70 per cent. You continue spreading, but plan to finish by 11:00.
• 10:45: The forecast shows the odds of exceeding your limit are now 80 per cent for midday. You decide to stop spreading before the wind picks up, having completed a significant amount of work.
• 12:00: You observe the wind has indeed increased, confirming your decision to stop. The instrument's record will show what was forecast and your decision.
• 17:00: You check the forecast for wind chill for the evening lambing. The instrument shows low wind chill risk, so you can proceed with your usual routines.

This approach allows you to adjust your plans in response to changing forecasts throughout the day, helping you maximise productive time while managing risks.

Your operational limits for wind are specific to your farm and the tasks you perform. For slurry or fertiliser spreading, your limit might be based on preventing drift onto neighbouring land, or optimising nutrient uptake by reducing ammonia loss. For lambing and calving, your limit will be based on the wind chill threshold that affects your young animals.

The instrument is preset to 2 metres, aligning with common working heights for these tasks. You can then input your specific wind speed limit into the instrument. This limit is not a universal standard, but rather what you have determined is appropriate for your specific machinery, spreading technique, or livestock management practices.

For example, while there is no legal wind limit for slurry spreading, your own experience might tell you that above a certain wind speed, drift becomes an issue. Similarly, for wind chill, you might have a specific wind speed combined with temperature that you know puts young lambs at risk.

By inputting your own limit, the instrument provides tailored information, showing you the likelihood of exceeding your personal operational threshold. This allows the instrument to work with your existing knowledge and practices.

The instrument keeps a dated record page of what was forecast, what was observed, the limit you used, and the call you made. This record is a factual account of the conditions and your decisions.

For your farming operations, this record serves several purposes. If questions arise about slurry spreading, such as concerns about drift, you have a clear record of the wind conditions you based your decision on. This can be useful for demonstrating good practice.

For livestock management, the record provides an overview of past wind chill conditions during lambing or calving seasons. This historical data can help you refine your understanding of how different wind conditions affect your animals over time, informing future decisions.

This record is a tool for accountability and continuous improvement. It allows you to review past decisions in light of actual conditions, helping you to refine your operational limits and decision-making process for future seasons.

Farming in Ireland is significantly influenced by its Atlantic exposure, which brings varied and often strong winds. The season for slurry spreading typically runs from January to April and again from July to October, outside of the closed period which begins around 15 October. Lambing and calving seasons, generally from February to April and January to April respectively, also require close attention to wind conditions, particularly wind chill for newborns.

These seasonal windows mean that farmers frequently need to assess wind conditions. The national forecaster, Met Éireann, provides general weather information, but your specific farm's microclimate and the precise height of your operations require more tailored data.

The need to manage ammonia loss from slurry spreading, as highlighted by organisations like Teagasc, means that wind speed is a critical factor in optimising nutrient use and complying with environmental guidelines. While there are no specific wind speed limits set by the Nitrates Action Programme, farmers use their judgement to avoid drift and maximise efficiency.

Understanding local wind patterns and forecasts at your working height is essential for making timely and effective decisions throughout these critical periods, balancing productivity with environmental considerations and animal welfare.