Field guide

What counts as a weather window

A weather window is a run of consecutive workable days long enough to cut, dry and bale before the rain comes back. A single fine day is pleasant; a window is fine days in a row with enough drying power in them for the crop you want to make.

BaleCast compares two independent forecast models (UK Met Office and ECMWF) and takes the wetter view whenever they disagree. A window only appears when even the cautious reading of the weather leaves room to finish the job — that is deliberate, so an alert is worth acting on.

Effective drying hours (EDH)

Not every daylight hour dries hay. An hour of strong sun with a breeze and low humidity takes far more water out of a swath than a grey, still, muggy one. Effective drying hours weight each forecast hour by sunshine, temperature, humidity and wind, so drying power adds up the way the crop actually experiences it.

As a rule of thumb, a hay crop needs around 40 EDH between cutting and baling; haylage needs much less because it is baled wetter. The outlook table shows each day’s EDH with dots: ●●● strong (10+), ●● fair (6+), ● slow (4+).

This is also why two "dry" days can behave so differently in the field — the EDH number is usually a better guide than the weather symbol.

Watch, likely and confirmed

Every window carries a confidence level. Watch means a window is forming but it is still some way out or the models disagree on the details. Likely means the models are broadly agreeing and the window is holding its shape run after run. Confirmed means both models agree and the window is close enough to plan around.

BaleCast is conservative on purpose — rain risk always uses the wettest model, and a window is only upgraded as agreement firms up. The aim is that when your phone buzzes, it is telling you something worth walking a field over.

Testing moisture in the field

A moisture meter with a probe is the quickest method: probe several spots along the windrow (or several bales), push the probe well in, and average the readings rather than trusting any single one. Readings swing through the day — grass carrying morning dew can read several points higher than the same swath at 4pm — so note whether you tested am or pm.

No meter? The twist test is the old standby: take a wisp of hay and twist it hard. If the stems snap and your hands stay dry, it is close to ready; if the twist feels damp or the stems bend without breaking, it needs longer. Scrape the outside of a few stems with a thumbnail too — moisture hides in the stem long after the leaf feels crisp.

The most accurate home method is oven- or microwave-drying a weighed sample: weigh out roughly 100 g, dry it in short bursts until the weight stops falling, and the loss as a share of the starting weight is your moisture percentage.

You can log readings against the harvest in the field log — choose Moisture test, and the latest reading shows on the harvest in progress.

Moisture targets for hay

Typical UK guidance: small square bales store safely below about 18% moisture; round bales below about 15–18%; big, dense square bales want drier still, nearer 12–15%, because tight bales hold heat. Above roughly 20% the risk of mould and heating climbs quickly, and hay baled in the mid-20s and above can heat dangerously in the stack.

For horse hay, aim for the dry end of those ranges. Mould spores are the enemy — they cause respiratory disease in stabled horses — so hay that would pass for cattle can still be wrong for horses. Never feed visibly mouldy hay to horses; if dust is a worry, many owners soak or steam before feeding.

These figures are rules of thumb: bale density, storage and weather at baling all shift what is safe. When in doubt, drier.

Moisture targets for haylage

Haylage is wilted rather than fully cured — typically baled at around 30–45% moisture (55–70% dry matter) after one to two days of wilting, then wrapped so it ferments instead of moulding. Horse haylage is usually made at the drier end, around 30–40% moisture.

The wrap does the preserving, so wrap within a few hours of baling, use enough layers (six is the common recommendation), and treat the wrap as precious — a pecked or torn bale lets air in and mould follows.

Baled much wetter than about 50% it ferments poorly and behaves more like silage; drier than about 30% and there may not be enough moisture to ferment at all, which puts you back into hay territory and hay moisture rules.

Soil testing through the year

Test each field every three to five years — most farms rotate a few fields each year rather than doing everything at once. Walk a W pattern across the field taking small cores to about 7.5 cm for grassland, avoid gateways, troughs, dung and feeding areas, and mix the cores into one sample per field.

Timing matters more than season: leave at least two to three months after fertiliser, lime, slurry or muck, and sample at the same point in the rotation each time so results compare fairly year on year.

A standard UK report gives pH plus phosphorus, potassium and magnesium, as an index or in mg/l. Common grassland targets are pH around 6.0–6.5 and P and K at index 2 — your lab or adviser will interpret against your cropping.

Log results in the field log — choose Soil test, enter pH, N, P and K, and add any extra readings your report includes (magnesium, calcium, sulphur, organic matter). Values are stored per reading so they can be graphed over the years as tests build up.