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Start with the grade

Steve’s first question is the same for every crop: tell me what your market wants. In wheat, the answer is the grade. It’s set at the silo, from a sample of your load: the protein in the grain, its test weight (how much a measured volume of it weighs), how much of it is small and pinched enough to fall through the screen, and whether rain at harvest has started it sprouting. A crop that misses its protein, or carries too many screenings, drops a grade, and every tonne of it is paid less.

So in wheat, the grade is the recovery. Tonnes that drop a grade are tonnes you grew and were paid less for. And the grade is settled long before harvest, step by step.

A round grain sieve with a slotted metal base, holding a heap of plump, even, golden wheat grains, and a few small grains fallen through below it. — In wheat, the grade is the recovery. It’s set at the silo, from a sample of your load: the protein in the grain, its test weight, how much of it is small and pinched enough to fall through the screen, and whether rain at harvest has started it sprouting. A load with too many screenings drops a grade, and every tonne of it is paid less. An illustration, simplified.

The same sieve holding mixed grain, many of the grains small, thin and pinched, with small grains falling through it into a heap below. — In wheat, the grade is the recovery. It’s set at the silo, from a sample of your load: the protein in the grain, its test weight, how much of it is small and pinched enough to fall through the screen, and whether rain at harvest has started it sprouting. A load with too many screenings drops a grade, and every tonne of it is paid less. An illustration, simplified.

A yield built in steps

Every wheat yield is three numbers multiplied together: the heads in a square metre, the grains in each head, and the weight of each grain. Each one is set at its own stage, in order. The heads come first, at tillering. The grains a head can hold are set as the stem runs up, and how many of them fill is settled around flowering. The weight comes last, in grain fill.

A later step can make up only a little for an earlier one. A thin crop grows slightly bigger heads, and a crop short of grains fills them a little heavier, but rarely enough to catch up. That’s Steve’s critical stages in one crop: each step is critical in its turn, and what it needs has to be there before it starts.

A young wheat plant with a main stem and four tillers fanning from its base; the two youngest tillers are yellowing and withering. — Heads in a square metre, times grains in each head, times the weight of each grain: each is set at its own stage. An illustration, simplified.

A green wheat ear after flowering, close up: grains swelling in most spikelets, but a few near its base and tip empty. — Heads in a square metre, times grains in each head, times the weight of each grain: each is set at its own stage. An illustration, simplified.

Tillers: how many heads

From about the third leaf, side shoots grow from the base of each plant, beside the main stem. They’re the tillers, and every tiller that lives makes a head. So tillering sets how many heads there can be. It starts with an even strike: seedlings coming up evenly across the paddock. A gap in the stand means heads the crop never has. Put phosphorus close to the seed, so the roots get away well. Phosphorus drives the tillers, too: short of it, a crop puts out fewer, and later.

Not every tiller makes it. Once the stem starts to run, the plant lets its youngest, weakest tillers die and feeds the rest. Short of nitrogen, it lets more go. Short of manganese, as wheat often is on alkaline sands, or of zinc, the whole plant runs slow.

A young wheat plant at tillering, cut away below the ground: a main stem and four smaller side shoots fanning from its base, and below, the old grain in the soil with fine roots spreading from it. — From about the third leaf, side shoots, the tillers, grow from the base of the plant, and every one that lives makes a head. Phosphorus close to the seed drives them. Once the stem starts to run, the plant lets its youngest tillers die and feeds the rest, and short of nitrogen it lets more go. An illustration, simplified.

From about the third leaf, side shoots, the tillers, grow from the base of the plant, and every one that lives makes a head. Phosphorus close to the seed drives them. Once the stem starts to run, the plant lets its youngest tillers die and feeds the rest, and short of nitrogen it lets more go. An illustration, simplified.

The head is made inside the stem

Here’s the step most growers never see. By the time the stem starts to run, the head is already forming inside it, down near the ground. Feel the base of a main stem: once there’s a firm bump just above the soil, the first node, the stem is running. By then the head has laid out its spikelets, and each one is forming its florets. Every floret is a grain that might be. Most won’t make it.

You can see it for yourself. Pull a main stem, slit it lengthwise from the base with a sharp knife, and look just above the first node. There’s the head: soft, pale and about a centimetre long, its spikelets stacked up both sides. A hand lens shows the florets forming in each one.

A young wheat plant as its stem starts to run: a main stem and four tillers fanning from its base, the two youngest yellowing and withering. — By the time the stem starts to run, the head is already forming inside it, down near the ground. In the weeks before flowering, the plant decides how many of its florets will make grain. Slit a main stem lengthwise from the base and you can see it for yourself. An illustration, simplified.

The base of a wheat stem, sliced in half lengthwise and magnified: layers of pale green leaf sheaths, a solid band across the stem a little above its base, and near the top, wrapped inside, a tiny pale young ear. — By the time the stem starts to run, the head is already forming inside it, down near the ground. In the weeks before flowering, the plant decides how many of its florets will make grain. Slit a main stem lengthwise from the base and you can see it for yourself. An illustration, simplified.

In the three or four weeks before flowering, the head grows fast, and the plant decides how many of its florets will make grain. A crop that’s short of water, nitrogen or sunlight then sets fewer grains, and nothing later puts them back. That’s why the weeks before flowering are a critical stage in wheat: the grains are counted before the head comes out.

So the foundation goes in before the stem runs: calcium for the cell walls, silicon for a stem that stands, and boron for the pollen to come. Copper is its own step, and it has to be in before the boot. The boot is the stage when the sheath of the top leaf, the flag leaf, swells round the young head. The pollen forms inside it. Short of copper then, the heads can come out empty, or partly empty.

The stem has to carry that head all the way to harvest. A thick crop pushed hard with early nitrogen grows tall, soft stems, and as the heads get heavy, wind and rain lay it flat: it lodges. A lodged crop fills poorly and is slow and costly to harvest. Silicon and copper stiffen the stem’s walls, and potassium keeps it firm.

A small stand of wheat at grain fill: five short, sturdy stems standing upright in red-brown soil, their heavy heads nodding a little. — A thick crop pushed hard with early nitrogen grows tall, soft stems, and as the heads get heavy, wind and rain lay it flat: it lodges. A lodged crop fills poorly and is slow and costly to harvest. Silicon and copper stiffen the stem’s walls, and potassium keeps it firm. An illustration, simplified.

A thick crop pushed hard with early nitrogen grows tall, soft stems, and as the heads get heavy, wind and rain lay it flat: it lodges. A lodged crop fills poorly and is slow and costly to harvest. Silicon and copper stiffen the stem’s walls, and potassium keeps it firm. An illustration, simplified.

Flowering: the grains set

The heads push out of the flag leaf’s sheath, and a few days later they flower, from the middle of each head outwards. Wheat pollinates itself, inside each floret: the yellow anthers you see hanging out have mostly done their work already. It’s over in a few days, and those days are fragile. A frost, or a run of hot days, at flowering can kill the pollen, and those florets stay empty. Frost follows the low ground. The Stress and salt page has more.

A green wheat head at flowering, close up: pale yellow anthers hanging from the spikelets in its middle, its tip and base still closed. — A wheat head flowers from the middle outwards, over a few days, and pollinates itself inside each floret: the anthers you see hanging out have mostly done their work. A frost, or a run of hot days, at flowering kills the pollen, and the florets flowering then stay empty. An illustration, simplified.

The same wheat head two weeks later: plump florets swelling with grain in its middle, and flat, empty ones at its tip and base. — A wheat head flowers from the middle outwards, over a few days, and pollinates itself inside each floret: the anthers you see hanging out have mostly done their work. A frost, or a run of hot days, at flowering kills the pollen, and the florets flowering then stay empty. An illustration, simplified.

Grain fill: the weight and the protein

Once the grains are set, they fill. Most of what goes into them is made after flowering, by the top leaves, the flag leaf most of all, and by the head itself, and the rest comes from sugar stored in the stems. So keep the canopy green and working as long as it can go. A hot, dry finish cuts the filling short, and the grain comes off small and pinched: light, and full of screenings. The Sizing and bulking page has more.

The top of a green wheat plant after flowering: a full ear, the broad green flag leaf below it, and the next leaf down. — Most of what fills a grain is made after flowering, by the top leaves and the head itself, and the rest is sugar the stem stored. Keep the canopy green and working as long as it can go: a hot, dry finish cuts the filling short, and the grain comes off small and pinched. An illustration, simplified.

The same wheat plant top after a hot, dry finish: the top leaves dead and curled, the stem yellow, the ear pale and thin. — Most of what fills a grain is made after flowering, by the top leaves and the head itself, and the rest is sugar the stem stored. Keep the canopy green and working as long as it can go: a hot, dry finish cuts the filling short, and the grain comes off small and pinched. An illustration, simplified.

The protein is made now too, from nitrogen. Most of it is moved out of the leaves and stems into the grain, and the rest is taken up as the grain fills. This is where Steve’s line about nitrogen is plainest: it’s a liability until it becomes a protein, and in wheat the protein is what the grade is paid on. Nitrogen early builds tillers and canopy, and so yield. Nitrogen later, from about the flag leaf on, goes more to protein. And the protein needs sulfur beside the nitrogen.

Early nitrogen can cost you too. Too much of it up front grows a big, thick crop that uses up the soil’s water before the grain fills, and if the spring turns dry, there’s nothing left to fill it with. Australian growers call that haying-off: a crop that looked great in winter comes off pinched. It’s the critical stages again: feed each stage for what it sets, not all of it at once.

This is where potassium has earned its place. It helps move the sugar into the grain, and keeps the plant standing and holding its water. Magnesium keeps the leaves green to the end.

Ripening, and the harvest

As the grain hardens, the heads and stems turn gold, and a thumbnail barely dents the grain. Nitrogen does nothing for it now, so hold the nitrogen. What’s left is the weather. Rain on a ripe crop can start the grain sprouting in the head, and a sprouted sample fails the falling number test and drops a grade, however good it was the week before. A crop that ripens evenly can come off the day it’s ready.

A ripe wheat head close up, golden and dry, its grains plump in their papery husks. — Once the grain is ripe, what’s left is the weather. Rain on a ripe crop can start the grain sprouting in the head, and a sprouted sample fails the falling number test and drops a grade, however good it was the week before. A crop that ripens evenly can come off the day it’s ready. An illustration, simplified.

The same wheat head after rain, dull and damp, with small white rootlets and a few pale green shoots coming out from between its husks. — Once the grain is ripe, what’s left is the weather. Rain on a ripe crop can start the grain sprouting in the head, and a sprouted sample fails the falling number test and drops a grade, however good it was the week before. A crop that ripens evenly can come off the day it’s ready. An illustration, simplified.

The season at a glance

About 170 days from sowing. The days are a guide: the crop’s stage is the clock. Build yours in the program builder.

1 · Sowing to emergence days 0–14

An even strike, and roots away fast.

How you know it’s here The first leaf spears up through the soil.

What matters most: Phosphorus Zinc Calcium
2 · Tillering days 14–60

Tillers set how many heads there can be to the square metre. Nitrogen and phosphorus drive them.

How you know it’s here Side shoots, the tillers, grow from the base beside the main stem, from about the third leaf.

What matters most: Nitrogen Phosphorus Manganese Zinc
3 · Stem elongation days 60–100Sap testCell division

As the stem runs, the head inside it sets how many grains it can hold. Silicon for a stem that stands, and copper before the boot, for the pollen to come.

How you know it’s here Feel the base of a main stem: the first node is a firm bump just above the ground.

What matters most: Silicon Boron Copper
4 · Heading and flowering days 100–120Sap test

Pollination: boron for the pollen, and a crop that isn’t under stress. Copper’s part came before the boot.

How you know it’s here The heads push out of the flag leaf’s sheath. A few days later, yellow anthers hang from the middle of each head.

What matters most: Boron Calcium
5 · Grain fill days 120–155

Fill the grain: the canopy’s work goes into the heads, and the protein is made now.

How you know it’s here Squeeze a grain: milky at first, then like soft dough.

What matters most: Potassium Magnesium Sulfur
6 · Ripening days 155–170

Dry down evenly. Hold the nitrogen.

How you know it’s here The heads and stems turn gold, and the grain is hard: a thumbnail barely dents it.

What matters most: Potassium

Where it fits in a program

Know the grade you’re growing for: its protein, and how many screenings a load can carry.
Get an even strike, with phosphorus close to the seed, and keep the tillers fed: nitrogen and phosphorus drive them.
Have calcium, boron and silicon in before the stem runs, and copper in before the boot.
Split the nitrogen: enough early for the tillers, and more later for the protein, with sulfur beside it, as the season’s rain allows.
Save potassium for grain fill. By then the crop has earned it.
On each walk, count the tillers, and later the heads, in a metre of row, and feel for the first node. Sap test before the stem runs and while it’s running, while there’s still time to act.

“Nitrogen is a liability until it becomes a protein.”

— Steve, on nitrogen