QUORUMAG

Quorum Ag · The wiki learn-wiki-mobile-immobile.html

Ideas · where to look

Mo­bile and im­mo­bile min­er­als

Old leaves or new? Episode 3 3 min read

The short version

Some minerals move around inside the plant; some mostly stay where they first land. When a mobile one runs short, the plant robs its old leaves to feed the new, so the old leaves show it first. When an immobile one runs short, the new growth goes without. Where a shortage shows tells you which kind to look for.

Two leaves off one plant. The old one gave up what it had to feed the new growth, so the shortage shows there first.

Two kinds of minerals

Some minerals move around inside the plant. Others mostly stay where they first land. It sounds like a textbook detail, but it tells you two practical things: where on the plant to look for a shortage, and when a mineral has to be there.

Where a shortage shows

When a mobile mineral runs short, the plant robs its older leaves to feed the new growth, so the old leaves show it first. When an immobile one runs short, the plant can’t borrow much of it, so the new growth goes without: the new leaves, the growing tips and the fruit.

the mineral, where it is in the plant.

  • A young bean plant: its oldest leaves, at the bottom, are yellow between green veins, and the leaves above are green.

    Move around

    nitrogen, phosphorus, potassium, magnesium

    short of one, the plant robs its old leaves for the new growth

  • The same young bean plant: its oldest leaves are green, and its youngest leaves, at the top, are pale and mottled between green veins.

    Stay put, or nearly

    calcium, boron (in most crops), sulfur, iron, manganese, zinc, copper

    short of one, the plant can’t borrow much, so the new growth goes without

Where a shortage shows first tells you which kind of mineral to look for: the old leaves for one that moves, the new growth for one that stays put. The paintings show magnesium on the old leaves and manganese on the new; other minerals can look quite different. An illustration, simplified.

A clue, not a verdict

Where a shortage shows is a clue, not a diagnosis. Plenty of things look alike on a leaf: a shortage, a mineral that’s there but locked up, a root problem, a pest, or a hot week. Check it with a test before you spend money on it. That’s where sap tests earn their keep: old leaves and new, side by side, show you what’s moving.

The mineral. Lime. Held back.

  • A young bean plant in red-brown soil: its older leaves green, and its youngest leaves, at the top, pale and mottled between green veins.

    Short in the soil

    a young bean, its new leaves pale

    the soil has little of it to give

  • The same bean in pale, chalky soil flecked with white, its youngest leaves pale.

    Locked up

    the same leaves, in limy soil

    plenty in the soil, held back from the roots

  • The same bean in red-brown soil, its youngest leaves pale, and its roots short and few, with brown tips.

    A root problem

    the same leaves, poor roots

    plenty in the soil, but the roots can’t take it up

Where a shortage shows is a clue, not a diagnosis. The same pale new leaves can mean a soil short of a mineral, a mineral that’s there but locked up, or roots that can’t take it up, and a pest or a hot week can look alike too. Check it with a test before you spend money on it. An illustration, simplified.

What it means for timing

Here’s the part that matters for your program. An immobile mineral can’t be borrowed later: it has to be on hand while the tissue is being built. That’s why calcium and boron, two of the foundation minerals, go in before the cell division window, not after the problem shows. And a foliar spray of an immobile mineral mostly stays in the leaves and fruit it lands on. The new growth that comes after it gets little or none.

A spray’s mist. The mineral, where it is in the plant.

  • A young apple shoot with five oval, toothed leaves and a small growing tip, growing up from older wood.

    Sprayed

    an apple shoot, a mineral that stays put

    the spray feeds the leaves it lands on

  • The same apple shoot some weeks later, grown on: four new, paler leaves above the five.

    Some weeks later

    the same shoot, grown on

    the old leaves keep what they got; the new growth gets little or none

A foliar spray of a mineral that stays put mostly stays in the leaves it lands on. The new growth that comes after it gets little or none, so time the spray to the growth it has to feed. An illustration, simplified.

How is it shifting?

Steve starts from a grower’s sap tests. A grower shows him a single number, and he asks: how is it shifting? That’s when, he says, you start to understand which minerals are mobile and which aren’t.

Follow the old leaves and the new through a season, and you see it for yourself: some minerals move, and some don’t.

A sap test of the new leaves. A sap test of the old leaves.

  • Five potato plants across one season, left to right: just emerged, young, in flower, full grown, and yellowing at the end.

    Magnesium: one that moves

    sap tests at the potato plant’s five stages, from just up to yellowing, as it runs short of magnesium

    the old leaves drop first: the plant moves magnesium out of them, to the new growth

  • The same five potato plants across the season.

    Calcium: one that stays put

    the same five stages, as the potato plant runs short of calcium

    the new growth drops, while the old leaves hold up: calcium stays where it is

Test the old leaves and the new side by side through a season, and you can see which minerals move. One that moves drops in the old leaves first, as the plant moves it out of them to the new growth. One that stays put drops in the new growth, while the old leaves hold up. An illustration, not real results.

“So now you’re starting to understand what minerals are mobile and not.”

— Steve, on reading sap tests