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Minerals · wood and pollen

Cop­per

In before the pollen Episode 3 8 min read

The short version

Copper is a trace mineral: a crop needs only tens of grams of it a hectare. It helps build lignin, the woody stiffening in cell walls that keeps stems standing and tissue tough, and it goes into the pollen. Short of copper as the heads form, a grain crop’s pollen fails and the heads come up empty, and by the time you can see it, it’s too late for that crop. Copper is also a spray, and that’s a different job.

Ripening wheat. The full heads bend over with their grain, and the empty ones stand up straight and pale: copper short as the heads formed is one cause, and frost at flowering another.

What it does

A crop needs very little copper: tens of grams a hectare, where it needs kilograms of the big minerals. But copper does jobs nothing else can. It helps build lignin, the woody stiffening laid down in the walls of cells. Lignin is what lets a stem stand, keeps the plant’s water pipes from collapsing, and makes it harder for a fungus to get in. Copper is part of the leaf’s engine too: it passes electrons along the chain that turns sunlight into sugar.

Copper. Lignin, the woody stiffening. A water pipe. A fungus’s threads. Stopped.

  • The top of a green wheat plant after flowering: a full ear, the broad green flag leaf below it, and the next leaf down.

    Stiff walls

    the top of a wheat plant, after flowering, and its stem’s wall, magnified

    copper helps build lignin in the walls: the stem stands, the water pipes stay open, and a fungus finds it harder to get in

A crop needs very little copper, but it does jobs nothing else can. It helps build lignin, the woody stiffening laid down in the walls of cells. Lignin is what lets a stem stand, keeps the water pipes from collapsing, and makes it harder for a fungus to get in. An illustration, simplified.

And it goes into the pollen. A plant short of copper as its flowers form makes poor pollen, or pollen that never gets out, and its flowers aren’t fertilised. Grain crops show it most: the heads come out, and there’s no grain in them.

In before the pollen

In wheat, barley and oats, the head forms inside the stem while the stem is running up, and its pollen is made in there, before the head pushes out of the boot. That’s when copper has to be in the plant. Short of it then, the heads come out empty, or partly empty, however good the crop looked before. By the time you can see it, it’s too late for that crop.

Copper. Copper missing.

  • The top of a wheat stem at the boot: the flag leaf’s sheath swollen round the young head, with a window cut in it showing the pale green ear inside.

    At the boot

    a wheat head, inside the stem

    the head forms inside the stem, and makes its pollen in there

  • A golden wheat stem at harvest, its full, heavy ear bending it over.

    With enough copper

    at harvest

    full of grain: heavy, so it bends over

  • The same wheat stem short of copper: a pale, bleached, empty ear standing straight up, and a late green shoot below.

    Or, short of copper

    at harvest

    empty: light and pale, and it stands straight up

Copper in before the boot while the pollen is forming inside the head

Copper has to be in before the head leaves the boot. Short of it as the pollen forms, the head comes out empty, and by then it’s too late for that crop. An illustration, simplified.

At harvest, the empty heads give it away. A full head is heavy and bends over. An empty one is light, and stands straight up, pale and bleached, often with late tillers still green below it. Frost or heat at flowering can do the same. So can a dry spell, or disease at the crown. Where the white heads sit in the paddock is a clue. Frost follows the low ground. A copper shortage follows the soil, often in patches on the sandier ground.

How a shortage shows

Copper moves very little inside a plant that’s short of it, so it’s the new growth that goes without first. The Mobile and immobile minerals page explains why. Each crop shows a copper shortage its own way:

  • Wheat, barley and oats: the youngest leaves go pale, their tips wither and die back, and some twist into a curl, often called pigtailing. Later, the heads come out white and empty, and late tillers keep coming.
  • Fruit trees: in summer, the shoots die back from the tip, the leaves near the tip drop, and gum can form in the bark. In citrus, the young twigs can split and ooze gum.
  • Onions: thin, pale skins that don’t stay on. See onions.
  • Vegetables: pale, limp young leaves that wilt easily.

Copper. Copper missing. Can’t move on.

  • A cut-away of a young wheat plant at tillering: several tillers of narrow, mid-green leaves, and fine roots spreading through red-brown soil.

    Enough copper

    young wheat, tillering

    every leaf green, old and new

  • The same wheat plant, its youngest leaves pale with dead, white-grey tips, two or three twisted into curls, its older leaves still green.

    Short of copper

    the same wheat

    copper barely moves, so the newest leaves go without: pale, the tips dying back, some twisted in a curl

Copper moves very little inside a plant that’s short of it, so the new growth goes without first. In wheat, barley and oats, the youngest leaves go pale, their tips wither and die back, and some twist into a curl, often called pigtailing, while the old leaves stay green. Later, the heads come out white and empty. An illustration, simplified.

What locks it up

  • Sandy soils. Leached sands hold very little copper to start with. Whole districts of Australian sand were only farmed once copper and zinc went on with the superphosphate, the Ninety Mile Desert in South Australia among them. Many of those soils still need it.
  • Organic matter. Organic matter holds copper tightly, so peaty soils, and soils very high in organic matter, can leave a crop short even when a test finds plenty there.
  • Plenty of nitrogen. Heavy nitrogen makes a copper shortage worse. The crop grows more, so it needs more copper, and it holds on to the copper in its old leaves instead of moving it to the new.
  • Zinc and phosphorus. A lot of zinc can cut how much copper gets in, and heavy phosphorus means fewer of the root fungi that help gather it.
  • High pH. Copper gets harder to get as the pH climbs, though less sharply than manganese or zinc do.

Copper. Copper missing. Held back: it can’t reach the root.

  • Three young wheat seedlings cut away below the ground, their fine roots reaching down through pale, loose sand.

    A sand

    wheat seedlings in a leached sand

    very little there to start with: the crop can go short

  • The same wheat seedlings in a dark, fibrous, peaty soil.

    A peaty soil

    the same seedlings, in a soil rich in organic matter

    plenty there, but held tight: a soil test finds it, and the crop can still go short

Two soils that can leave a crop short of copper. A leached sand holds very little to start with. Organic matter holds copper tightly, so a peaty soil, or one very high in organic matter, can leave a crop short even when a test finds plenty there. An illustration, simplified.

A spray, and a trace

Copper is also one of the oldest sprays there is. Sprayed on, it sits on the leaf and kills the spores of fungi and bacteria that land there, before they get in. That’s protection on the outside, not feeding: little of it gets into the plant. It has to be on before the disease, and put back after rain.

Unlike most sprays, it never breaks down. Year after year of copper sprays builds copper up in the topsoil, and in some old orchards and vineyards there’s now more than the life in the soil can stand: earthworms are among the first to go. So the copper you spray isn’t the copper your crop needs. Feed the crop what it’s short of, spray only what the disease calls for, and ask why the disease is there. See pests and plant health.

Copper. A fungus’s spore. A spore, killed.

  • A grapevine leaf with a dried, pale blue-green speckle of copper spray over its upper surface.

    On the leaf

    a vine leaf, after a copper spray (the circle: its skin, magnified)

    it sits on the outside and kills the spores that land: protection, not feeding

  • The soil under a young vine, cut away: dark crumbly topsoil threaded with fine roots, and pink earthworms in their burrows.

    A young vineyard

    its topsoil

    earthworms, and the life with them, all through it

  • The same soil under the same vine, decades on, with no earthworms or burrows left in it.

    Decades of sprays

    the same topsoil, decades on

    the copper never breaks down: it builds up, until the life there can’t stand it

Copper sprayed on a leaf protects it from the outside, and little of it gets in. It never breaks down, so year after year it builds up in the topsoil. In some old orchards and vineyards, the earthworms are among the first to go. An illustration, simplified.

When it matters most, crop by crop

The stages where copper is one of the minerals that matter most, in the program builder’s seasons. Each bar is a whole season, from sowing or planting to harvest, or a tree’s year. Build yours in the program builder.

  • Potatoes about 120 days

    Tuber initiation (hooking) · Tuber bulking · Maturation

  • Beans about 70 days

    Cell division · Cell expansion and sizing

  • Onions about 180 days

    Bulb initiation and cell division · Bulb filling and maturation

  • Wheat about 170 days

    Stem elongation

  • Apples a year

    Leaf drop and winter wash · Deep dormancy · Wood wash before bud break · Tight cluster to first pink

Where it fits in a program

  • Know your soil. A copper shortage runs with the soil: sands, peaty ground, and paddocks with a history of it.
  • In cereals, have it in before the boot: in the soil before sowing, or as a spray from late tillering through stem elongation.
  • Copper put into the soil lasts for years, often decades. Once a paddock has had a dressing, it’s built up, not used up in a season.
  • A spray feeds the leaves it lands on, and little moves on from there, so time it to the growth that needs it.
  • Don’t pile it on. Copper stays in the soil for decades once it’s there, and too much harms the roots and the life around them.
  • Check before you spend. Young leaves withering at the tips could be several things, and white heads could be frost. A test of the youngest leaves helps tell them apart, though copper is hard to read on a test.
  • Rates come from your tests, your agronomist and the label. Never a guess.