Zinc
Function of Zinc
Zinc (Zn) acts as a catalyst in the processes of oxidation in plant cells, and is vital for the transformation of carbohydrates. It regulates the consumption of sugars, which provide energy for the production of chlorophyll. It plays a part in the formation of growth promoting compounds within the plant, and it aids in the absorption of adequate moisture. Zinc is a major component in seed, grain formation, in plant height, protein synthesis and crop maturation date.
| Soin Zince (Zn) Index System | |
|---|---|
| Soil Status | Soil Zn Range (mg/l) |
| 1 | <1 |
| 2 | 1.01-1.50 |
| 3 | 1.51-3.00 |
| 4 | >3.00 |
Deficiency risk – Main Factors
1. Soil pH > pH 6.0 Zn availability decreases.
2. High soil organic matter - low Zn availability.
3. Loose, unconsolidated seedbeds and poor root - soil contact.
4. Continuous arable soils with low soil organic matter levels.
5. Zn is low on acid brown earths, acid sands, soils derived from granite, and in clay soils with low magnesium.
6. High phosphate soils and >pH 7.0 reduce Zn availability.
7. High N application will reduce Zn availability
| Critical Zinc levels PPM in Soil- Soil pH and soil P | ||
|---|---|---|
| Deficiency | pH > 7.0 P > 15.0 | pH < 7.0 P < 15.0 |
| Severe | <1.0 | <0.6 |
| Moderate | 1.0 - 1.5 | 0.6 - 1.0 |
| Slight | 1.5 - 2.0 | 1.0 - 1.7 |
| None | >2.0 | >1.7 |
Deficiency Symptoms
Zn deficiency generally shows up in the early stages of growth, when the plant is only a few inches high, appearing first as yellow streaks in the young leaves with a white to yellowish tip. White spots often appear in the leaves or along the edges and a portion of the marginal area my die. Frequently the entire plant is stunted, due to shortening of the internodes.
Diagnosis & Treatment
Zn deficiency can be diagnosed from knowledge of crop symptoms, susceptible soil types and field history. Leaf analysis will confirm a deficiency and is a cheap diagnostic test compared to the cost of Zn application. Zn is deficient in cereals at less than 20mg/kg in plant tissue. Soil analysis is an excellent and a reliable guide to diagnosis or prediction of Zn deficiency.
Foliar application
– Good crop response & will reduce grain yield loss
- Chelated products which offer advantages of much greater compatibility with other agrochemicals, better solubility and no risk of crop scorch.
- Inorganic suspensions; these proprietary products are based on Zn sulphates, Zn oxides as a flowable suspension, together with stickers & wetters in a tank mixable formulations.
- Split foliar Zn app. (2 by ½ rate) – Improved crop response
Spring Cereals
To maximize crop uptake and response to foliar Zn split, apply 50% at 3 – 5 leaf stage and the remaining 50% at 1st node to flag leaf visible
Winter Cereals
Autumn, as well as spring, Zn sprays are need on cereals (esp. wheat & barley) if deficiency symptoms develop during the autumn. Apply foliar Zn at GS 25 in fields where moderate to severe Zn deficiency is a known problem in most years. Spring application of Zn to winter cereals should be applied by GS 31.
Interactions
Very high levels of N, P & K may induce Zn deficiency. Fe or Mn, either in excess or deficient, may be contributing factors to Zn deficiencies.