Know your Zinc application options

IPF Agronomist – David McRae

As time passes from the application date, the residual value of zinc (Zn) fertilisers generally reduce. This, combined with the location of the applied Zn fertiliser relative to active root growth and moist soil, will influence Zn availability for plant uptake during each season – and from season to season.

Therefore, continual Zn application each cropping season will help ensure plants have access to adequate Zn nutrition. Application options, such as pre-plant, at planting and foliar, can be used by agronomists and growers to maximise yield potential.

The role of zinc in the plant

Zn plays a key role in a wide range of enzymes and proteins, controlling many important biochemical pathways. These are mainly concerned with:

• carbohydrate metabolism, both in photosynthesis and in the conversion of sugars to starch.
• protein metabolism.
• auxin (growth regulator) metabolism.
• pollen formation and viability.
• maintenance of the integrity of biological membranes.
• resistance to infection by certain pathogens.
• detoxification of oxygen radicals to protect cells.
  

Maintaining optimal plant nutrient concentrations may become more difficult with increased temperatures as plant growth rates will increase, intensifying the nutrient uptake period.

Management of soil nutrient levels, soil structure, moisture conditions and irrigation scheduling may need to be reviewed to respond to altered plant requirements.

High risk zinc deficient situations

Soil properties that have a high risk of reducing Zn availability are:

• low levels of available or total Zn.
• calcareous.
• salt-affected.
• pH > 7.
• fields that have been laser levelled.
• high phosphorus status or applications.
• low organic matter.
  

Environmental conditions:

• waterlogged soils and stressed crops.
• cool, wet periods that reduce root growth.
• crops affected by herbicides which reduce root growth.
  

Plant deficiency symptoms

Zn deficiency symptoms can appear throughout the crop growth cycle. Figures 1, 2 & 3 illustrate classic Zn deficiency in maize, sorghum and cotton, but sub-optimal nutrient concentrations (hidden hunger) can be more widespread and go undetected.

Monitoring crop nutrient concentrations with leaf and petiole testing allows levels to be recorded and fertiliser or management practices altered. It is important to sample the correct plant part and growth stage as interpretation information is only available for selected situations. Refer to plant sampling guide in Nutrient Advantage Pro software or Plant Sampling for Agriculture (Dowling and Blaesing 2022).

Plant requirement for Zinc

Plant Zn uptake occurs from establishment to grain development. Plants generally only require small quantities of Zn but accessing crop requirements can be challenging in early growth stages as plants generally have small, ineffective root systems.

The factors listed above (high risk zinc deficient situations) have a large influence on the plant availability of soil Zn. Zn concentrations in the soil solution are generally very low and this, combined with small root systems of young plants, is the reason banded starter Zn fertiliser is applied at planting (Alloway 2004).

Depending on inherent Zn fertility, placement of pre-plant and starter Zn fertiliser and moisture availability, plants may be able to access sufficient Zn to satisfy crop demand. In situations that the surface soil is dry for extended periods, intermittent water logging and phases of rapid plant growth, soils often cannot supply crop requirements and supplementary Zn is required.

If Zn deficiency limits early season growth or reduces reproductive fertility, final crops yields will be reduced. Supplying plant available Zn throughout the crop growth cycle helps ensure the best outcome. Once a crop has sufficient leaf area, foliar Zn applications are an effective method of supplying plant available Zn.

Incitec Pivot Fertiliser (IPF) Zinc solutions

IPF has a comprehensive range of Zn fertilisers that can be applied to either build soil Zn levels, maintain adequate plant Zn concentrations, or alleviate deficiency symptoms. There is an effective IPF product for both soil and foliar applications.

Soil applied – preplant or planting

EASY LIQUIDS Zn-SUL is sulphate based and can be sprayed onto the soil surface and incorporated into the seed bed to build soil Zn levels. It can also be used as an in-furrow injection at planting.

IPF has a range of products and blends which contain Zn, which are usually spread and incorporated pre-plant to build soil Zn availability. These products utilise Zn from GRANULOCK^® Z and Zn monohydrate and can be tailored to your requirements.

GRANULOCK Z can be applied at planting in the seed furrow to supply Zn. It is generally applied at 20-25 kg/ha with summer crops.

EASY LIQUIDS KEYPRO ZINC is an EDTA chelated form of Zn which is ideal for soil application. It is more efficient than other forms at supplying plant available Zn from soil applications. It can be applied in furrow at planting time with FLOWPHOS 13Z.

In-crop foliar – broadcast or banded (boom spray or Inter-row cultivation)

EASY Liquids P-FOL ZINC is a Zn phosphate fertiliser that can be applied as a band or broadcast spray to prevent and correct Zn and or phosphorus deficiency.

EASY GLY ZNP contains chelated Zn and phosphorus and can be sprayed with Glyphosate to Roundup Ready cotton with no reduction in weed control. EASY GLY ZNP is easy to handle and safe on the crop.

EASY Liquids ZING is a Zn sulphate fertiliser that can be applied as a band or broadcast spray to prevent and correct Zn deficiency.

Product	Nitrogen (N)	Phosphorus (P)	Potassium (K)	Zinc (Zn)
EASY GLY ZNP	2% w/v	3% w/v	7.4% w/v	7.2% w/v
EASY LIQUIDS KEYPRO ZINC			9.2% w/v	9% w/v
EASY LIQUIDS P-FOL ZINC		18% w/v	3% w/v	14% w/v
EASY LIQUIDS ZING	8.6% w/v			10.7% w/v
EASY LIQUIDS ZN-SUL				16% w/v
GRANULOCK Z	11.6% w/w	21.8% w/w		1% w/w

For further information, please feel free to contact David McRae david.mcrae@incitecpivot.com.au or 0477 987 321 and Bede O’Mara via bede.omara@incitecpivot.com.au or 0417 896 377

References

• Dowling CW and Blaesing DT (2022) Plant Sampling for Agriculture – A Guide, Fertilizer Australia, Canberra, Australia. Plant Sampling (fertilizer.org.au)

• Zinc in soils and crop nutrition, B. J. Alloway (2004)