The four-course rotation, field drains and the seed drill
Run the fields as one system: a rotation whose fodder crops feed the stock and whose manure feeds the grain, wet land underdrained so it can be worked and sown, and grain drilled in rows at a known rate and depth so it can be counted and hoed.
Everything for this step
- Field guide
- Sustainable farming → 9 sections
- Builds
- None yet.
- Reference sheets
- 1 sheet in Sustainable farming
- Sciences it rests on
- Agricultural science · Earth sciences · Biology
- Track
- Crops and soil, level 4 of 7 · next: Drip and sprinkler irrigation
Why this matters
A tier-1 farm rotates with a legume and returns manure (open ground and hold fertility). Tier 3 adds three things that let the same land carry more. A fodder root and a clover ley in place of bare fallow keep every field cropped and feed animals through the winter, so the manure that returns to the grain grows with the herd. Drains under wet clay let it be worked and sown on time; a mole channel drawn 600 mm deep every 2.75 m or less carries water to pipe drains below (field drainage specification). A seed drill puts seed at a set depth in rows: wheat sown at 375 seeds/m² in early October establishes about 70 %, 260 plants/m², and can be counted and hoed (AHDB, Wheat growth guide).
The shape of it
- Rotate four fields through cereal, fodder root, cereal and a clover ley, so no field lies bare and the stock eat the roots and the ley.
- Return the manure to the cereal fields; a good legume ley adds about 50–200 kg of nitrogen per hectare a year.
- Lime to the soil test: most crops grow best between pH 6 and 7.
- Underdrain wet land: pipe drains with at least 600 mm of cover in clean 5–50 mm gravel, and in clay, mole channels 600 mm deep and no more than 2.75 m apart drawn across them.
- Drill the grain in rows about 4 cm deep at a known rate, and add 50 plants/m² for each month sowing is delayed.
- Count the plants with a quadrat, and hoe between the rows while the weeds are small.
Doing it, step by step
The summary above says what has to happen. This says how, with the numbers that decide whether it works.
1 · Lay out the four-course rotation as a farm system
Divide the arable land into four fields of about equal size and move each crop one field on every year:
- Wheat, or another winter cereal.
- A fodder root — turnips, swedes or mangels — sown in rows and hoed, eaten by sheep and cattle through the winter.
- Barley, or oats, with the clover sown under it.
- A clover ley, grazed or cut for hay, and ploughed in before the wheat.
The root and ley years are what replace bare fallow: every field grows something every year, the animals eat half the rotation, and their manure goes back on the cereal fields. The principle — at least three crops, one of them a legume — and the nitrogen a ley fixes are in open ground and hold fertility and the farming guide.
2 · Lime before the clover
Test the soil's pH before liming, field by field: most crops grow best between pH 6 and 7 (soils guide). Spread burnt or ground lime from Lime on the stubble before the barley that will carry the clover, and work it in.
Lime corrects acidity slowly. Retest the same fields every rotation and lime again only when the pH has fallen below the range.
3 · Underdrain the wet fields with pipes
Land that stays waterlogged after rain cannot be ploughed or sown on time and grows little. Lay pipe drains — fired clay tiles from brick and tile, or perforated plastic — in straight lines at a steady fall set with a level, never with a dip, to a ditch (field drainage specification, UK National Association of Agricultural Contractors):
- At least 600 mm of cover over every drain.
- Clean permeable backfill of stone between 5 and 50 mm over the pipe, kept free of soil.
- A rigid outfall pipe at least 1.5 m long into the ditch, with a grating against vermin, hinged outwards.
Record the line, depth and outfall of every drain on a map: a drain nobody can find cannot be cleared.
4 · Draw mole channels across the pipes in clay
In heavy clay, water reaches the pipes too slowly through the solid subsoil. A mole plough — a bullet-shaped foot on a blade, followed by a larger expander — draws an open channel through the clay that carries water to the gravel over the pipes (the same specification):
- Depth: the channel's floor ideally 600 mm and never less than 500 mm below the surface, deep enough to cut the gravel over the pipes, and at least 100 mm above the pipe.
- Spacing: no more than 4.5 × the depth and never more than 2.75 m between channels; no less than 3 × the depth.
- Size: circular, at least 75 mm across.
Mole only in clay, when there is enough moisture at moling depth to make it plastic and form a smooth, round, stable channel, and the surface is dry enough to crack above it (NAAC).
5 · Drill the grain in rows at a known rate and depth
A seed drill opens a slot, drops seed at a set rate and covers it, row after row, so every seed sits at the same depth and the rows can be hoed. The AHDB Wheat growth guide for winter wheat:
- Depth: about 4 cm, deeper where slugs or birds take the seed.
- Rate: a benchmark of 375 seeds/m² sown in early October, of which about 70 % establish, 260 plants/m².
- Late sowing: for each month drilling is delayed, about 50 more plants/m² are needed, because the plants have less time to tiller.
- Target: about 150 plants/m² in the thinnest parts of the field, more where weeds compete.
Calibrate the drill before the season: turn it over a sheet for a measured distance, weigh what falls, and adjust until it matches the rate.
6 · Count the plants, then hoe the rows
Count once the crop is fully established (AHDB): lay a 0.5 × 0.5 m quadrat diagonally across the rows in 10 representative places, count the plants inside, average the counts and multiply by 4 for plants per square metre.
Hoe between the rows while the weeds are seedlings: the first weeks decide the harvest (plant staples). Rows wide enough for a horse-hoe let one person keep a field clean that hand-weeding could not.