How to grow soybean

Only lime if a soil test — or past crops that stayed small and yellow even with fertiliser — tells you the soil is sour. Your recommendation gives the exact amount for your field.

Spread it evenly over the whole field, like sprinkling flour by hand. Patches give patchy results — some plants nodulate and thrive, the rest stay starved.

Work it into the topsoil with a hoe or plough. Lime only helps the soil it is mixed into; left on top it does almost nothing.

Do it 2–3 months before you sow — a good time is right after clearing the last crop. Lime is slow, so late liming won't help this season.

Buy the variety and seed amount your recommendation gives. Soybean is fussy about day-length — the wrong variety flowers too early or too late — so your plan has already matched the variety to your area and season length.

Ask for Bradyrhizobium inoculant — the powder of living root germs (rhizobia) that lets soybean feed itself. Check it is in date and has been kept cool and out of the sun; the germs are alive, and heat kills them.

Buy the basal your recommendation gives. Soybean wants phosphorus and potash (and sulphur if it's listed), but almost no nitrogen, because it makes its own. Don't let a dealer sell you a high-nitrogen compound for it.

Store seed and fertiliser dry, off the floor, away from food, water and children, and keep the inoculant in the coolest, darkest place you have — a fridge if you can — until sowing day.

Count out 100 seeds at random from the bag. Handle them gently — soybean seed bruises and cracks if you pour or drop it hard.

Lay them on a wet cloth or newspaper, roll it up loosely, and keep it warm and damp (not dripping) for about a week; wet it again if it dries out.

Unroll it and count how many have sprouted a root or shoot and look normal — throw out the twisted or rotten sprouts.

80 or more out of 100 → good seed, sow it. If your count is only just over 80, sow a little thicker to make up for it.

If it fails — fewer than 80 sprout — don't sow this seed. Take it back to the dealer or buy fresh certified seed, or you'll get a thin, gappy crop you can't fix later.

Clear weeds and old crop residue off the planting lines so the small seed meets firm, clean soil.

Loosen the soil to about 15–20 cm — a spade's depth — and break any hard pan underneath so roots and water can go down.

Break the clods to a fine, crumbly tilth, then firm the surface lightly. Seed sown into big clods or loose fluff comes up patchy.

Level the surface so water can't pool — soybean roots rot in standing water. On a slope, work across the slope and make ties or ridges to hold the rain.

Use only well-rotted manure or compost — dark, crumbly, no strong smell. Fresh, strawy manure needs more time to rot down.

Spread it evenly and thinly — about one wheelbarrow-load over a patch 10 strides by 10 strides (≈100 m²), which comes to the 5–10 tonnes a hectare your plan is built on.

Work it into the topsoil 1–2 weeks before you sow, so it settles in with the soil.

Work in the shade. Make a little sticky water — a spoon of sugar in a cup of clean water — and dampen the seed just enough for the powder to cling.

Sprinkle on the Bradyrhizobium powder (the living root germs) and turn the seed gently until every seed is coated dark. Use all the powder the packet gives for your seed amount — more is better — and keep handling it gently so you don't crack the seed.

Sow the same day, ideally within a few hours. Never leave coated seed in the sun or overnight — heat and sunlight kill the germs.

Sow on a real planting rain that wets the soil a spade deep. Open furrows about 50 cm apart — half a stride — and drop seed about 3–4 cm deep — one finger-joint — no deeper, because the seed-leaves must push up out of the ground.

Space the seed about 6 cm apart — two finger-joints, roughly 16 seeds along each stride (1 m) of row. Run the basal phosphorus/potash along the furrow and cover it with a little soil, so it sits near the seed but not caked against it.

Cover and firm the soil gently, so each seed sits snug in moist earth and comes up strongly.

Twice a week, walk a large "W" across the field so you cover the corners and the middle, not just the edge by the path.

At about 10 stops, look closely at 10 plants — the growing tip and the stem right at ground level.

Cutworms: look for young plants cut clean off at ground level, worst in the morning. Scratch the soil nearby to find the fat, grey, curled caterpillar.

Damping-off: look for seedlings that have rotted or pinched thin at the soil line and toppled over, often in damp patches or where the soil has crusted. The stem stays rotted-but-attached — not sliced clean like a cutworm's.

Count the gaps (stations with no plant) so you know whether to gap-fill, and write down what you see and where.

About 7 to 12 days after sowing (a week to 10 days), walk the rows and count how many plants are up against the number of seeds you sowed.

Work out the share that came up — for example, 85 plants where you sowed 100 = 85%.

85% or more → a good, even stand — carry on.

If it fails — below 85% — gap-fill the biggest blanks in the next few days, while the soil is still moist and the crop is only days old. Leave it, and the gaps become weed patches you can't recover.

Re-sow only the biggest gaps while the soil is still moist and the crop is only about a week old — later fills never catch up with the rest.

Coat the fill-in seed with the root-germ powder just like the first sowing, and sow it the same day.

Sow at the same 3–4 cm depth — one finger-joint — and firm the soil so the seed meets moisture.

Keep the topsoil moist but not waterlogged from sowing through the first few weeks.

Water every 5–7 days, more often in heat and on sandy soils that dry fast.

Check by pushing a finger in: water when the top few centimetres are dry. Drain any low spots where water pools.

Twice a week, walk the "W" and check about 10 plants at 10 stops — the leaves, the growing tips, and now and then a root.

Soybean mosaic virus: look for leaves that are mottled light-and-dark green, puckered and crinkled, on stunted plants. There's no cure — pull out and carry off badly affected plants so aphids don't spread it further.

Aphids: look for tiny soft green or black insects clustered on the shoot tips and leaf undersides, with sticky leaves and black sooty mould. A few do no harm; only act if they build up fast, since they also spread the mosaic virus.

Root-knot nematode: where plants are stunted and yellow in patches, dig one up and look for knobbly swellings that are part of the root itself (galls) — different from the good nodules, which are loose beads on the side of the root that rub off cleanly.

Write down what you see and where, so you can tell whether it's spreading.

Start early — by about 10 days to 2 weeks after sowing — and weed again every 10–14 days until the canopy closes (roughly 6 weeks after sowing).

Hoe shallowly between and within the rows. Soybean roots and nodules sit near the surface, so deep hoeing close to the plants tears them and cuts the nitrogen supply.

Pull big weeds close to the plants by hand, rather than chopping near them with the hoe.

In dry areas, leave the pulled weeds lying between the rows as a mulch to hold moisture.

About 3 to 4 weeks after sowing, gently dig up one or two plants with a ball of soil — don't pull them, or you'll strip the nodules off and leave them in the ground.

Wash the roots and look for pea-sized lumps (nodules). A good crop carries plenty, especially on the main root.

Slice a few nodules open. Pink or red inside = they're making nitrogen — do nothing, the crop is fed.

If it fails — few or no nodules, or they're pale, grey or green inside — they aren't working. Top-dress a little nitrogen to carry the crop, and next season use fresh, well-kept inoculant. If the leaves are pale and yellow too, act sooner rather than later.

Water only every 7–12 days through this stage, and let the crop lean a little dry rather than keeping it soaked.

Don't let it wilt badly, but this is the time to stretch your water if supply is short.

Keep your water back for the flowering and pod-fill stages ahead — that's where every drop pays back most.

From the first flowers (about 6 weeks after sowing), check weekly — and every few days in warm, wet, cloudy weather, which rust loves.

Look low in the canopy first, at the undersides of the older leaves near the ground, where rust starts.

Rust looks like: many tiny tan or brown raised bumps (pustules) on the leaf underside, later with yellow blotches on top and leaves dropping early. Rub one and a fine rust-coloured powder smears off on your finger.

Frogeye leaf spot may show too: small round spots with pale grey centres and reddish-brown rings, like little frog eyes, on the upper leaves.

The moment you find rust on even a few plants — before 1 leaf in 10 is spotted — spray (see the fungicide task). After that point the spray can't save the crop.

Spray at first flower (about 6–8 weeks after sowing) in rust-prone areas, or the moment scouting first finds rust.

Measure the dose with the cap supplied and mix it into a full knapsack (15–20 L). Follow the label — more is not better.

Spray to wet the leaves, including the undersides where rust lives, until they glisten but don't drip.

Protect yourself: wear a long-sleeved shirt, cover your nose and mouth, spray in the cool of the day with the wind behind you, and keep children and animals off the field.

Wash yourself and the sprayer afterwards, and keep the spray off any food crops growing nearby.

Respect the pre-harvest interval — the number of days the label says to wait between spraying and harvest, so the chemical fades from the crop before you eat or sell it. Don't harvest early after spraying.

Keep the soil moist right through flowering — water every 5–7 days, more often in heat.

Never let the crop wilt now, even for a day — wilting at flowering sheds pods you can't get back.

If your water is limited, this stage and pod-fill come first — take water from the vegetative stage, not from here.

From about 8 weeks after sowing, check every few days through pod-fill — the leaves, and now the pods themselves.

Rust: keep checking the undersides of the lower leaves for the tan-brown pustules, and spray again if it's still spreading (see the second-fungicide task).

Pod-sucking bugs: look for green or brown shield-shaped bugs on the pods; they leave shrivelled, flat or spotted seeds and give off a foul smell when squashed.

Pod borers (bollworm): look for round holes chewed in the pods, caterpillars eating the seeds inside, and dark droppings left on the pods.

Squeeze a few pods to feel whether the seeds are filling plump, and note anything that's spreading so you can act.

Spray again about 2–3 weeks after the first fungicide (roughly 9–11 weeks after sowing) — but only if scouting shows rust is still spreading.

Measure with the cap supplied, mix into a full knapsack (15–20 L), and spray to wet the leaves and their undersides without dripping.

Cover up as before — long sleeves, nose and mouth covered, wind behind you, people and animals off the field — and wash yourself and the sprayer afterwards.

Mind the pre-harvest interval (the wait between spraying and harvest that the label sets). With harvest getting close, count the days left before you'd cut — if there aren't enough, don't spray.

Keep the soil moist through pod-fill — water every 5–7 days, more often in heat.

Don't let the crop wilt while the pods are filling; the seeds shrink and never recover the weight.

Only once the lower leaves start to yellow and the pods begin to turn should you ease off, to let the crop dry down for harvest.

From about 3.5 months (14 weeks) after sowing, watch the crop turn: the leaves yellow and fall, and the pods change from green to brown or tan.

Shake a plant — when about 95% of the pods are brown and rattle with loose, hard seed inside, the crop is mature.

Bite a seed: at readiness it cracks rather than dents (about 13–15% moisture — 13 to 15 parts water in every 100).

If it's not there yet — still green and soft — wait a few days and check again; seed cut early won't keep. Once it's ready, harvest promptly before the pods dry too far and shatter.