Author: Reily Menhenett – Technical Agronomist, Incitec Pivot Fertilisers

Understanding trace element levels in a paddock can be challenging, both in cropping and pasture scenarios. Soil tests are often not sensitive enough to provide a true indication of the plant available levels of these dynamic micronutrients.

Although required in smaller amounts, trace elements are just as essential to a plant’s growth and life cycle. Understanding and diagnosing deficiencies is therefore critical for effective nutrient management. Using plant tissue testing clarify exactly how much of each nutrient a plant is accessing in the soil, and whether the levels are sufficient, or limiting to production.

Plant tissue trends

The following insights are drawn from 5,300 plant tissue samples submitted to Nutrient Advantage between 1 January 2020 and 1 August 2025. The graphs show samples from agronomy zones in Victoria and South Australia, split by enterprise into pasture and cropping samples.

Critical values for micronutrients differ between plant species and time of sampling. Table 1 summarises values considered subcritical for most crop and pasture species, as well as a corresponding percentage of samples below that range.

For samples that fall below the critical value, it is likely production may be limited by that nutrient. For an accurate representation of any one crop at a given growth stage, it is recommended to submit a sample to the Nutrient Advantage Lab, for comprehensive testing and determination of critical concentrations.

Table 1 Summary of leaf tissue micronutrient levels

 Critical Value (mg/kg)Pasture samples below critical valueCropping samples below critical value
Boron<512%23%
Copper<21%5%
Molybdenum<0.215%26%
Zinc<2018%33%

Source: Incitec Pivot Fertilisers

Boron

As shown in Figure 1, 12% of all pasture samples fall into the subcritical category, with a further 28% in the low range of 5-10mg/kg.

Given the narrow range between deficient and toxic for boron, it is important to consider whether a system may be limited by other factors first, before applying boron. More information about boron in pasture production can be found here.

Figure 1: Boron levels – Pasture samples from agronomy zones in Victoria and South Australia. Source: Incitec Pivot Fertilisers.

In cropping (Figure 2) the proportion of samples below the critical value was higher, with almost one quarter of samples submitted below 5mg/kg.

While the overall nutrient balance of a crop can cause dilution of micronutrients in some tissue samples, the overall result indicates boron may be a limiting factor in some crop types.

Boron is particularly influenced by liming and a deficiency may be induced by high rates applied to correct soil acidity.

For more detailed information on the availability and role of boron, click here.

Figure 2: Boron levels – Cropping from agronomy zones in Victoria and South Australia. Source: Incitec Pivot Fertilisers.

Copper

Copper availability in pastures is critical for both plant function and animal demand. For ruminants, copper deficiency can be induced by high rates or sulphur or molybdenum, or deficiencies in pasture material.

Although only 1% of samples fall below the critical value of 2 mg/kg, a further 27% are within the borderline range of 2-5mg/kg, indicating levels across the regions are generally low.  

If you need to apply copper there are several options (including granule blends or spray on coatings), depending on product and rate requirements. Typically, copper is applied to the soil at 1 to 2 kg/ha. How long the application remains effective will depend on climate, soil, and nutrient management. 

If copper has not been applied to a pasture for several years, it could be worth considering applying a low rate with the autumn SuPerfect application, followed by a tissue test in winter or spring to assess copper levels in the pasture. 

For more information on the role of copper in pastures and its importance for animal health, click here.

Figure 3: Copper levels – Pasture from agronomy zones in Victoria and South Australia. Source: Incitec Pivot Fertilisers.

As with the pasture samples, Figure 4 shows that only 5% of cropping samples fall under the critical value of 2mg/kg, however a further 45% are in the low range of 2-5mg/kg.

Copper deficiency rarely produces characteristic symptoms in the field – slight to mild deficiencies usually go undetected. Severe copper deficiency symptoms in cereals typically cause twisting of the flag leaf and empty or partially-filled heads (‘rat tailing’). Malformation of the heads can often be attributed to frost, so it can pay to check with a leaf tissue test.

For detail on the role of copper in the plant, please see the copper Agritopic here.

Figure 4: Copper levels – Cropping from agronomy zones in Victoria and South Australia. Source: Incitec Pivot Fertilisers.

Molybdenum

Molybdenum in pasture systems is particularly important for legumes. While the requirement for plant tissue is small, rhizobia bacteria (responsible for nitrogen fixation) require approximately 10 times that of the plant. The role of molybdenum in grasses should not be discounted either. Deficiency can lead to accumulation of nitrates in grass tissue, potentially causing poisoning for stock.

While 15% of sample submitted are below 0.2mg/kg, it is worth acknowledging that many in the 0.2-1.0 mg/kg range may also benefit from molybdenum, particularly if legumes comprise a large portion of the pasture.

If a deficiency is detected, it can be corrected by applying 50-75 gMo/ha every 5-7 years. This application, sprayed onto granules, ensures even distribution across the paddock and helps maintain optimal molybdenum levels, supporting the N-fixing process and promoting healthy plant growth. For more information, click here

Figure 5: Molybdenum levels – Pasture from agronomy zones in Victoria and South Australia. Source: Incitec Pivot Fertilisers.

In cropping, and in particular, pulses – molybdenum is critical for nodulation and healthy growth of rhizobium.

Acid soils are particularly problematic for molybdenum. Absorbed as an anion, molybdenum becomes less available as pH drops. For this reason, liming can improve molybdenum availability. Generally, it is not recommended to lime and apply molybdenum in the same season to avoid potential toxicity.

For detailed information about molybdenum, see the IPF Agritopic here.

Figure 6: Molybdenum levels – Cropping from agronomy zones in Victoria and South Australia. Source: Incitec Pivot Fertilisers.

Zinc

Of all the micronutrients, zinc is most reliably tested in soil sampling. Soil test levels in conjunction with plant tissue sampling should be considered when deciding on a fertiliser zinc plan.

Based on this data set, zinc is generally well supplied in pastures, with only 18% falling below 20 mg/kg.

For further information on zinc applications in pasture, see the 2024 Agronomic Insight here.

Figure 7: Zinc levels – Pasture from agronomy zones in Victoria and South Australia. Source: Incitec Pivot Fertilisers.

In cropping, deficiency in zinc seems more widespread, as shown in Figure 8. Zinc is very immobile in soils so anything that reduces root growth can induce zinc deficiency in crops. For this reason, growing conditions – for example cool soils, herbicide applications, pest or disease pressure – as well as the zinc fertiliser application history in crop will have a large effect on access and uptake of zinc. Foliar sprays can be effective to treat the problem in season, however, to fix the root cause of the deficiency, application of a fertilizer to the soil is more effective. Granulock Z is particularly effective in solving zinc deficiency, as zinc is compounded in every granule for even distribution in furrow at planting. In some cases, good growing conditions can help a crop to ‘grow out’ of a deficiency through greater root exploration, however if a deficiency is critical, applying zinc is likely to help protect yield.

For insight into zinc and its importance in cropping systems, see the Agritopic available here.

Figure 8: Zinc levels – Cropping from agronomy zones in Victoria and South Australia. Source: Incitec Pivot Fertilisers.

Micronutrient availability

Soil pH and environmental conditions often play a large role in plant uptake of micronutrients. Availability dynamics by pH are shown in Figure 9. Apart from molybdenum, micronutrients are more plant available when soils are more acidic, with the best availability of all nutrients observed between pH 5.5 and 6.5. Potential toxicities of iron and manganese at low pH, or molybdenum at high pH are also factors to consider when thinking about micronutrients.

For these reasons, applications of lime and their influence on trace elements availability should be considered. As shown in the graph, alteration of pH can have an outsized effect on availability in the soil.

As always, when deciding to fertilise with micronutrients, the context around a deficiency is important to consider. For pastures, rumen dynamics – for example copper-molybdenum antagonism – are particularly important, with applications of trace elements likely to have an impact on animal health, as well as plant health. In cropping situations, consideration should be made to time of year and other factors such as waterlogging before pulling the trigger on an application.

Figure 9: Availability of micronutrients. Source: Incitec Pivot Agronomy in Practice 2025. Source: Incitec Pivot Fertilisers.

Tips for implementing tissues testing well

Tissue testing is often reactive and used as a diagnostic tool. Whilst this can help with identifying if a nutrient is the constraining factor to production, it is sensible to monitor crop performance year to year with tissue testing to understand what the plant is accessing.

Often, tissue testing is the last piece of the puzzle in a nutrient budget, allowing a grower or advisor to determine whether their strategy was optimal for a given season.

Tissue testing is relatively simple and requires no special equipment, just a clean pair of rubber gloves and a sample bag. Spring is a great time to take tissue tests in pastures, while plants are actively growing, and it is easy to select a good representative sample avoiding urine and dung patches.

When tissue testing, it is important to ensure the sample is collected at the right growth stage, and that the correct plant part is taken for analysis. Sampling technique is also important to minimise potential contamination – particularly of micronutrients.

A short video on tissue testing in pastures is available here.

The FertCare guidelines for tissue sampling can be found here.

Summary

Often overlooked, tissue testing is a critical tool to understand plant performance, for both cropping and pasture enterprises. While micronutrients are required in smaller amounts, they are just as essential to growth and productivity. As shown in the Nutrient Advantage Laboratory data, micronutrients are potentially limiting production – both of crops and pastures in the southern agronomy region.

In pasture systems, tissue testing offers insights that go beyond plant health, extending into animal nutrition and wellbeing. Deficiencies in copper, for example, can impact ruminant health, while molybdenum plays a key role in nitrogen fixation for legumes and can influence nitrate accumulation in grasses. Spring is a particularly valuable time to test pastures, providing a snapshot of nutrient status during active growth and helping inform decisions for the season ahead.

In cropping, tissue testing helps identify subtle deficiencies that may not present clear symptoms in the field. It allows growers to fine tune their nutrient strategy, respond to seasonal challenges and protect yield potential.

Whether in pasture or cropping systems, rounding out nutrient budgets with tissue testing is a sound strategy – not only to correct deficiencies for this season, but to get a head start of planning a fertiliser program for next season.

Further information

For more information on the tissue testing or trace elements, feel free to email IPF’s Technical Agronomist, Reily Menhenett at reily.menhenett@incitecpivot.com.au, or call on 0474 093 167.