Turnout to Grass — What Satellite Data Tells You That Your Eye Doesn't

You've been eyeballing turnout timing your whole life. Your father did too. You look at the field, poke the ground with your boot, check the forecast, and make a call. Most of the time it works. But some years you turn out too early, poach a field, and spend the summer looking at the damage. Other years you wait too long and burn through silage you didn't need to feed.

Satellite data doesn't replace your judgement. But it adds a layer of information your eye genuinely cannot see — and it's free.

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What satellites actually measure

The Copernicus Programme — the EU's Earth observation system — operates Sentinel-2 satellites that pass over Ireland every five days. They capture images in wavelengths your eye can't see, including near-infrared. From these images, you can derive:

• NDVI (Normalised Difference Vegetation Index) — a measure of how actively grass is photosynthesising. Green, growing grass scores high. Dormant or bare ground scores low.
• Soil moisture estimates — how wet the ground actually is beneath the canopy, not just how it looks on the surface.
• Growth trend over weeks — whether a field is on an upward trajectory or has stalled.

This isn't theoretical. PastureBase Ireland, run by Teagasc, already integrates satellite-derived growth data for farms across the country. The Grass10 programme uses this data to benchmark grass utilisation nationally.

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How to use satellite data for turnout timing

Step 1: Check your farm on PastureBase

If you're already recording grass measurements in PastureBase, you'll see satellite-estimated growth rates for your paddocks. These estimates update every time a clear Sentinel-2 image is available (roughly every 5 days, cloud cover permitting).

Look for paddocks where growth has consistently been above 10-15 kg DM/ha/day for the previous two weeks. That's a field that's actively growing and can handle grazing pressure.

Step 2: Cross-reference with soil conditions

Satellite NDVI tells you about the grass, but turnout also depends on whether the ground can take the weight. Met Éireann publishes soil moisture deficit data — check their agri-meteorology section. If the soil moisture deficit is close to zero or negative, the ground is saturated. Even if the grass looks ready, you'll poach the field.

An AI assistant can help here. Ask ChatGPT, Claude, or Gemini:

"Current soil moisture deficit for [your county] is X mm. I'm considering turning out 40 suckler cows onto a well-drained loam paddock. What's the poaching risk?"

The AI will combine what it knows about soil types, stocking density, and moisture thresholds to give you a sensible assessment.

Step 3: Compare fields side by side

This is where satellite data earns its keep. You might have ten paddocks and need to pick the best three for early turnout. Looking at NDVI maps, you can rank fields by:

• Current grass cover (higher NDVI = more cover)
• Growth trend over the past fortnight (rising = ready, flat = not yet)
• Aspect and drainage (south-facing, free-draining fields warm up first)

PastureBase can show this comparison. If you want raw satellite imagery, the Copernicus Browser (free, no account needed) lets you view your farm's Sentinel-2 images directly.

Step 4: Set a grass wedge baseline

Before turnout, record the average farm cover. PastureBase will calculate this from your measurements. If average farm cover is below 500-600 kg DM/ha, you're turning out into a deficit and you'll be back feeding silage within a week. Satellite estimates can fill gaps where you haven't walked every paddock with a plate meter.

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What satellite data can't tell you

• Sward quality — NDVI measures quantity of green biomass, not whether it's ryegrass or docks.
• Parasite burden — a lush-looking paddock might have a high worm larval count from autumn grazing.
• Real-time weather — the satellite image is from the last clear pass, not right now. Always check the Met Éireann five-day forecast before committing.
• Individual animal readiness — body condition, health status, and vaccination schedules still need your vet's input.

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What it costs

• PastureBase: Free to register and use.
• Copernicus satellite data: Free. Open access, no account required for the browser.
• Met Éireann data: Free on their website.
• AI assistants (ChatGPT, Claude, Gemini): Free tiers available. Paid tiers around €20/month.

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Where to get help

Your local Teagasc Grass10 advisor can walk you through PastureBase setup and show you how to read satellite-derived growth data. If you're in a discussion group, ask your facilitator to include a satellite data demo at the next meeting — it takes ten minutes and changes how you look at your farm.