Why one field yields more than another

Mostly, it's water — how much the soil can hold and how well it gets rid of the excess. After that come compaction, pH and nutrient status, position in the rotation, headland losses, and vermin. The detail matters less than one observation that holds on nearly every farm: the differences repeat. The field that topped the farm this year topped it five years ago, and the one that dragged the average down has been doing so for as long as anyone can remember.

That persistence is the useful part. It means two or three seasons of per-field records will separate the causes you can fix from the ones you're stuck with — and tell you which fixes actually pay.

Water first: depth, texture, drainage

A crop's yield is set, more than anything, by how many days it can keep photosynthesising through grain fill. Deep, moisture-retentive soil keeps a wheat crop green through a dry June; a shallow soil over chalk or gravel starts shutting down in the first rainless fortnight. That difference alone can be 2 t/ha between fields on the same farm, in the same season, under identical management.

Drainage is the other half of the water story. A field that sits wet drills late, roots shallow, and loses plants over winter — so it starts every season behind. Broken or silted drains show up as the same wet patches, in the same corners, every year. Of all the causes on this list, drainage is the one where spending money most reliably gets it back, because a drained field improves every crop that follows for decades.

Compaction: the same gateway, every year

Traffic causes compaction, and traffic is not evenly spread. The gateway end of a field takes every pass of every operation; the headlands take the turning; the mid-field takes far less. Years of this — especially harvest traffic in wet autumns — builds a pan that roots and water struggle to get through.

The tell is a field that yields respectably in a kind season and falls apart in a wet or dry one, because compacted soil punishes both extremes. It's fixable, but only if you know which fields (and which ends of which fields) have the problem.

pH and nutrient indices

Low pH quietly caps yield before any deficiency symptom shows — below about pH 6 on mineral soils, cereals start leaving yield behind, and the fix is among the cheapest per tonne recovered in the whole business. Fields at the far end of the farm, awkward to reach with the spreader, are the usual suspects for drifting indices. Soil sampling on rotation isn't exciting, but a low-P field wearing an average fertiliser plan will underperform indefinitely and never announce why.

Rotation position

A first wheat after beans and a third cereal are different crops wearing the same name. If your records show one field always disappointing, check what it's always following — some fields end up parked in the worst rotational slot for years through sheer habit and geography.

Headlands, shade and edges

Headlands commonly yield 10–20% below mid-field: extra traffic, overlapped or missed inputs, and turning damage. Trees and tall hedges on the south side cost a strip of yield to shade and moisture competition. Small fields are nearly all edge — which is a big part of why the awkward 3 ha paddock never matches the 20 ha block, and never will. And a field's shape changes its measured yield another way too: if margins have gone in and the cropped area has shrunk, yield calculated on the old area looks worse than it is — see measuring field area.

Vermin

Rabbits along a warren bank, pigeons on the rape next to the wood, deer in anything near cover. The losses are real, local, and — usefully for diagnosis — they map to geography, not management. If the poor strip is always the strip by the wood, you have your answer.

What the differences are worth

Take a 15 ha field yielding 1 t/ha below the farm's better wheat ground. At £180/t, that's £2,700 a year, every year, walking off that one field. Against that:

• If the cause is drainage, a repair scheme has a clear payback you can calculate — often just a few seasons.
• If it's pH, the lime to put it right may cost less than one year's lost output.
• If it's shallow soil over gravel, no spend fixes it — the right response is cheaper inputs and honest expectations, not more of everything.

Same symptom, three very different answers. The records are what tell them apart.

The records that make it actionable

One season of field yields is trivia — any single year can be excused by weather. Three seasons of weighed, moisture-adjusted, per-field figures is a diagnosis: the persistent underperformers stand out from the unlucky ones, and the causes above can be matched to each. Field histories covers what to record; benchmarking your yields covers how to compare fairly once you have the numbers, and the UK crop yield benchmarks give the context.

The pattern is nearly always there. Most farms just haven't written it down yet.

Frequently Asked Questions

Why do headlands yield less than the middle of the field?

Extra traffic and turning compact the soil, and input overlaps and misses are concentrated there. As a rough guide headlands run 10–20% below mid-field, which is also why small, awkwardly shaped fields — which are mostly headland — rarely match big open blocks.

How much yield difference between fields is normal?

On most mixed-soil farms, 1–2 t/ha between the best and worst wheat fields in the same season is unremarkable, and bigger gaps aren't rare where soil depth varies. What matters is whether the same fields sit at the bottom every year — persistent gaps have causes, and some of them are fixable.

Is it worth draining a poor-yielding field?

Often, yes — drainage is the yield-limiting factor with the most reliable payback, because it improves establishment, rooting and timeliness for every following crop. Run the numbers: a field losing 1 t/ha on 15 ha at £180/t is giving up £2,700 a year, which pays for a lot of pipe over a decade.

How many seasons of records do I need before acting?

Two seasons will separate the obviously persistent problems from bad luck; three gives you real confidence, since it will usually include both a wet and a dry year. Don't wait for perfect data before fixing the things you can already see — standing water and pH results don't need three years of yield maps to justify action.