Zinc in Plants: What It Does and When Your Crop Needs It

Zinc also helps build proteins and chlorophyll, keeps cell membranes whole, and is needed for pollen to form. In palay it decides how fast a young crop recovers after transplanting and how many tillers it makes.

A helper, needed in grams

Zinc is a helper, not a building block. It works like the key to an engine: it switches enzymes on and goes on working without being used up. That is why a crop needs only a few hundred grams of zinc per hectare, while it needs nitrogen by the bag.

But a helper that is missing stops the whole engine. A field short of zinc cannot use its nitrogen, phosphorus or potassium well, so every peso of fertilizer earns less.

Where zinc shows first

Zinc moves poorly inside the plant, so the shortage shows on the young and middle leaves. In palay the midrib of the young leaves turns pale, then dusty brown spots and streaks spread on the older leaves, and the plants stay short and uneven. In mais a broad white or yellow band runs down each side of the midrib.

See zinc deficiency for the signs in each crop.

When zinc in plants is most critical

Zinc matters most at the very start. In flooded palay the shortage shows two to four weeks after transplanting, when the young roots work hardest and the flooded soil holds zinc tightest. In mais and vegetables it is the first weeks of growth.

DAT means days after transplanting, DAS days after sowing in the field, and DAP days after planting. The days are the usual ones for a typical variety, so a long or short variety moves them a little. Timing zinc in plants to these windows gets more harvest from the same bags. Our guide to fertilizer timing by growth stage puts them together for a whole season.

Here is when each crop needs it most, from the anee.io stage book:

Rice, corn and other grains

Vegetables and legumes

Root crops, sugarcane and banana

When zinc comes too late

• Palay, transplanted: Zinc after flowering only raises grain zinc, not yield.

What keeps zinc from the crop

Most zinc problems come from the soil holding it, not from a soil without it. Alkaline, limy and sodic soils lock zinc up, and so does a paddy kept flooded for a long time. Heavy phosphorus makes it worse.

Soils low in organic matter, sandy soils and fields leveled by cutting away the topsoil also run short. Cold weather and young roots slow uptake further, which is why the shortage is often worst early and fades as the crop grows.

Where zinc comes from

Zinc sulfate is the usual choice, on the soil before or at planting, or dissolved and sprayed when the signs show. Some complete and foliar fertilizers also carry zinc. See micronutrients for rice and nutrient deficiency in rice.

• Zinc sulfate (heptahydrate or monohydrate): on the soil or as a foliar spray.
• Zinc chelate: a liquid that works well on alkaline soil.
• Zinc oxide: slower, as a coating or in blends.
• Dipping rice seedling roots in zinc mixed with water before transplanting.

Zinc questions