Because zinc availability is chemically limited rather than geologically scarce. It falls sharply as pH rises, so calcareous and over-limed soils lock it up even when total zinc is adequate, and high available phosphorus induces zinc deficiency within the plant, so heavily phosphate-fertilised ground often shows it. Those two factors cover a large share of the world's arable land.
2
What do zinc deficiency symptoms look like?
Interveinal chlorosis on young leaves combined with shortened internodes, which gives the characteristic rosetting or little-leaf habit. Because zinc is immobile in the plant, symptoms appear on new growth rather than on older foliage, which distinguishes it from magnesium deficiency. Leaf tissue analysis is the reliable confirmation.
3
Which hydration state carries more zinc?
The monohydrate, at around 35 percent zinc, against roughly 22 percent for the heptahydrate. The difference is water of crystallisation, which is inert weight, so the hydration state must be specified when comparing prices or calculating application rates. The heptahydrate dissolves faster and suits fertigation and foliar use.
4
Is zinc fertilisation relevant to human nutrition?
Yes. Zinc is a limiting nutrient in diets heavily dependent on cereals, and cereals grown on zinc-deficient soils carry less zinc in the grain. Agronomic biofortification, applying zinc fertiliser specifically to raise grain zinc content rather than only to raise yield, is an established public health strategy in several countries.
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