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FAQ: Other Nutrients

Trace Elements

Q. Can you build trace element levels in the soil?

Answer – In a continuous tillage systems it will be quite difficult to build soil trace element levels in the soil as tillage units are now specialized units. (No livestock enterprises). Where straw is chopped and cultivated back into the soil will help return and reduce the decline of soil trace elements. Organic manures offer the best opportunity to build soil trace element levels over time as for example pig / poultry / FYM / SMC etc can contain significant amounts of Cu, Mn & Zn.

Base fertilisers can also have trace elements added this would be a good nutrition policy where soils are low in trace elements. There is very little work carried out in this area so it is difficult to quantify changes in soil trace element status over time.

Q. What soil tests are available to measure soil manganese and how accurate are they at predicting a soil Mn deficiency?

There are a number of tests to determine the soil Mn. For example the total Mn test – This test is a very poor indicator of the soils available Mn status and very poor in detecting a Mn deficiency. Total Mn is generally used in combination with Cobalt, as the total Mn goes above 600ppm and soil Co is <3.0mg/kg there is the risk of Co deficiency in livestock.

ER Mn (Easily reducible Mn) the 2nd test that was developed and is currently tested for by Johnstown Castle is the ER Mn. This test is a great indicator / predicator of a Mn deficiency in tillage crops. The ER Mn measured in the soil is strongly related to the Mn in the plant tissue therefore a good predicator of Mn sufficiency / deficiency. Where the ER Mn is <80 mg/l there is a high risk of a Mn deficiency during the growing season.

Q. Can Cu improve the efficiency of N uptake by a cereal plant?

Cu is important in plant function (A component of several enzymes, with roles in photosynthesis, respiration, protein and carbohydrate metabolism, lignification and pollen formation) but there are no indications that it improves the uptake of N by the plant.

Q. What yield responses are expected in cereal crops grown on a low soil Cu site?

Research work would show up to a 14 – 15% grain yield response to cereals grown on low Cu status (0.5mg/kg) soils. This response was received by applying 0.5l/ha of Cu oxychloride applied as equal splits at Zadocks GS 22/30 & GS 31/32.

Another trial investigate the effect of a foliar application of Cu, Mn & Zn applied in equal splits as above combined with 3 N rates – 0, 150 & 200kgN/ha to create different yield levels. A significant yield response was obtained at the 150kgN/ha (+10%) but no yield response at the high N rates which produced 9.2 – 9.4 ton/ha. This would indicate that the non – pH dependent mobilization of Cu increases as fertiliser N rate is increased, probably due to greater production of chelating agents in root exudates by high yielding, vigorous cereal crops.(Scottish research 1984/85) 

Do higher yielding crops have a higher Cu requirement / demand?

It would seem logical that higher yielding crops would have a higher requirement for Cu as there would be larger crop off takes in grain & straw. A research trial tested soil applied Cu oxychloride combined with 3 N rates 0, 150 & 200 kgN/ha. A yield response of 22 – 25% was obtained on the 0 N treatments despite a moderate soil Cu status of 1.6 – 2.1 mg/kg. There was no yield response to Cu at the 150 – 200 kg N/ha rates despite the doubling of the plant Cu off take in those treatments which had nil Cu but received fertiliser N. Soil solution measurements at these two sites showed that mobilization of Cu into soil solution in the root zone soil, which occurred through the season in N –fertilized plots gave similar concentrations of Cu to those plots with nil N. This trial concludes that high yielding crops maybe more efficient in obtaining Cu from the soil, given similar levels of extractable soil Cu prior to seed sowing, as far greater mobilization of Cu occurs under a high yielding crop. Thus reducing N input may lead to an increase in Cu deficiency in cereal crops. On soils with low soil Cu status apply appropriate Cu soil / foliar product. In addition the above would indicate that a well developed root system is a key factor to ensuring sufficient Cu uptake by the plant. 

Q. Why will high soil pH reduce Mn availability in the soil & consequently result in crops deficient in Mn?

High soil pH will result in depressed Mn levels in the soil as Mn becomes absorbed on to soil surfaces and not plant available.

Q. Will high levels of soil P reduce the availability of Mn for plant uptake?

High soil P status will result high levels of P in plant tissue and lower levels of Mn in plant tissue. It has been suggested that the high soil P results in elevated P levels in the plant tissue that interferes with the uptake and or translocation of Mn , rather than a direct effect of soil chemistry on Mn availability.

Q. What effect will soil pH have on Mn availability?

As the soil pH increases by 0.1 of a unit above soil pH 7.0 Mn availability in soil water theoretically drops 10 times.

Q. What is the type of trace element source in Epso Combi top?

The formulation of Mn & Zn is in water soluble sulphate form.

Q. How effective is the application of Zn to the soil in meeting crop Zn requirements?

Zn can be broadcasted to the soil and cultivated in (20 kg/ha Zn sulphate). This will have a residual effective for a couple of years. Soil and foliar application in combination tend to be the most effective method to supplying the plant with sufficient Zn rather than soil or foliar application alone. Zn can also be applied to the seed but will require a foliar application to meet crop Zn requirement.

Q. What is the difference between sulphur deficiency and Zn deficiency in cereals?

Sulphur deficiency in cereals is generally identified as a pale yellowing of the youngest growth (Leaf) on the crop. Zinc deficiency shows pale crop growth with severe crop stunting and maybe confused with S deficiency (Zn deficiency will affect both old & new leaf growth, S def only affect new growth). Zn deficiency is generally most noticeable at early stages of growth. Symptoms of Zn deficiency in severe cases may appear as yellow streaks on the younger leaves of barley and wheat. Also on barley white streaks may appear along leaf edges. Often the entire leaf margin maybe bleached. The growing point may die in severe deficiency and plants remain stunted. Wheat will also be stunted due to reduced expansion of the internodes

Q. Where straw is chopped and cultivated in, how available is the trace elements from the straw?

Where straw is chopped and incorporated it will become available for plant uptake over the following growing seasons. For example a 3t/ac of spring barley straw crop will contain in the region of 225gMn, 9g Cu & 55g Cu.

Q. Tillage crops grown in high soil Mo areas, will lime application reduce Cu availability to the cereal plan

No. Apply lime as per soil sample lime recommendation (pH, crop and lime to target soil pH.)

Q. Can Mn & Zn be applied to the seed before sowing?

Yes seed can be treated with either Mn / Zn. In sites that are severely deficient in Mn / Zn, it can be the best approach to ensure the plant will not suffer a deficiency in the early stages of root and shoot development. It is essential on Mn deficient soil types as Mn has a key roll to play in root and tiller development in cereals. In addition P placement can be beneficial on a Mn deficient site as P will stimulate a large root structure therefore meaning more soil exploration resulting in more Mn uptake by the plant. The crop will still require Mn/Zn supplementation but will ensure good establishment in the early stages of the cereal plant.

Q. Are some varieties of barley more susceptible to Mn deficiency than others?

Research work from Denmark would show that winter & spring barley varieties react differently to Mn deficiency. The correct choice of variety can be very important in areas that are very predisposed to Mn deficiency. Winter barley seemed to be more sensitive as indicated from Danish work. The Mn programme adopted for winter barley was 2 autumn applications & 1 spring application of Mn sulphate. Winter barley varieties sensitive to Mn deficiency: Antonia, Resolut, Regina, Hanna, Platine, & Vanessa. Varieties that are tolerant to Mn deficiency are Carola, Rafiki, Ludo & Siberia.

Q. Is there any trace elements in ground limestone?

Amounts would be very small.

Q. Will seedbed consolidation reduce the incidence of trace element deficiencies?

Seedbed consolidation during soil cultivations - ploughing & sowing time is a major factor in reducing trace element deficiencies during the crops growing season.

Good seedbed consolidation improves the contact between soil and root, increasing the uptake of Mn, Zn & Cu. Poor seedbed consolidation will provide one of the best early warning signs of Mn deficiency – look out for better (darker green) growth in tractor wheel tracks.

Q. What effect will temperature and soil moisture have on trace element availability?

Soil temperature has a major influence on the availability of soil trace elements, during cold periods when soil temperatures are low crops may suffer a shortage of minor nutrients. As soil temperatures increase availability will increase. Soil moisture also has a major role to play in nutrient availability as nutrients are taken up in soil solution. During dry periods in combination with poorly consolidated seedbeds which will dry out easily resulting trace element shortages. Therefore seedbed consolidation is critical to retain soil moisture and ensure sufficient moisture for plant uptake of trace elements.

Q. Will seedbed preparation influence Mn availability?

Good seedbed preparation will reduce the incidence of trace element deficiencies and increase there availability i.e. soil cultivations under suitable soil conditions.

No Mn Spray

Mn Spray Soft Firm Soft Firm

Grain yield (t/ha) Broadcast N, P& K 3.6 4.9 5.5 5.8 Combined drilled N, P &K 5.0 5.2 5.9 5.9 SAC

From the above a number of factors are identified in reducing the incidence / effect of Mn deficiency in spring barley

Q. Will seed depth have an effect on Mn availability?

Sow seeds no more than 2.5cm as this will encourage a good and stronger root development / system.

  Seed Depth No Mn Spray Mn Spray
4cm 2cm 2cm
Grain yield (t/ha)
Broadcast N, P& K   2.8 3.7 5.1
Combined drilled N, P &K   - 5.8 6.1

Q. Can trace elements be applied as a fertiliser and how effective are they in meeting crop requirements?

Yes trace elements can be added to base fertiliser. This is an effective way to apply trace elements to a cereal crop and will ensure no shortage during the early stages of establishment and will ensure good root development and tiller development. There is little work monitoring change in soil trace element status overtime where fertilisers plus trace elements are applied. On severely deficient sites depending on the type of soil applied trace element and its availability there maybe the need to apply a foliar trace element application to the crop.

Q. What is the best time to apply foliar trace elements to cereals?

The best time to apply foliar trace elements is when the crop is actively growing when air and soil temperatures are good. Apply from GS 13 - 15 up to GS 32. Generally a little and often is good therefore split trace element applications and apply at least 2 – 3 times where a severe trace element deficiency is expected.

Q. Will foliar applied trace elements build the level of trace element in the soil?

No, foliar trace elements are applied to meet the crops requirements during the growing season with little or no soil residual effects.

Q. What are the trace element level in organic manures?

Organic manures are an excellent source of plant / soil trace elements and are the only way to restore or build soil trace element levels in soils.

Concentrations of trace elements calculated gr/ton (wet weight) stored solid manure & slurry (Steineck et al, 1999, Sweden)
  Cattle Pig
  Organic Conventional Conventional
  Solid Slurry Solid Slurry Solid Slurry
Mn 34 15 38 22 63 25
Zn 24 11 32 18 180 55
Cu 4.5 2.0 4.8 2.9 30.4 14.4

Poultry litter can also be a very good source of trace elements.

Q. What is the difference in leaf symptoms between Mn & Cu deficiency?

For Mn deficiency green veins are seen on new leaf growth. Cu deficiency the leaf will show yellow veins.

Q. What is the soil Mn Index?

See table below for the Mn index .

Soil ER-Mn IndecSoil ER- Mn ranges (mg/l)
11 <90.0
2 90.1-120
3 >120

Q. Can trace elements be applied to the soil to correct a nutrient deficiency?

Yes, soil applications of Cu & Zn are very effective at sowing time to reduce the risk of a deficiency. Mn needs to be applied as a seed dressing or a foliar spray.

Cu - apply 2.5 – 5.0kg Cu sulphate (25%) as a soil applied spray and cultivate(work into soil) into the soil as Cu tends to be very immobile in the soil. Where the soil is very deficient double the rate to 5 - 10kg/ha. The treatment will be effective for at least 5 years and probably 10 years. A crop spray is a useful insurance in the first crop after soil treatment with a 0.5l/ha of Cu oxychloride or equivalent foliar spray.

Zn can also be applied to the soil a Zinc sulphate (22%) (water soluble) at 5kg/ha (broadcast to soil). Crop foliar applications of Zn are very effective in reducing a crop deficiency and meeting crops requirements (e.g. – chelates, zinc oxides, EDTA chelates ,inorganic nitrates etc).

Mn application to the soil is not successful as Mn tends to get bound and locked up in the soil. To improve the uptake and availability of soil applied Mn to a cereal crop it is necessary to apply and place Mn with an acidic base fertiliser at sowing time to increase Mn availability to the crop during establishment. The most effective fertiliser regime for Mn is Mn treated seed followed by foliar Mn spraying.

Q. Will fertiliser placement (N, P & K) at sowing time reduce induce T.E. deficiencies?

Yes and no! It will reduce deficiencies due to the fact that there will be a larger root system developed by the plant therefore allowing the plant to explore a larger volume of soil. In addition due to rapid development for example a zinc deficiency can be induced on low Zn soils due to rapid plant development and low soil supply. In conjunction with the above where a site/ soil is deficient in anyone or combination of trace elements the crop will require a suitable trace element programme to reduce a loss of grain yield applied at the correct time with a suitable product.

Q. What is a hidden trace element deficiency?

A hidden trace element deficiency is one in which the plant shows no signs or symptoms in visual plant characteristic. There may not be differences until the plant comes close to harvest for example plant height difference, time of maturity etc for example a winter wheat crop can suffer a 30% yield loss to a Mn deficiency and show no visual crop symptoms or signs detected. For example cereals crops can suffer a 20% yield loss to a deficiency of Cu and show no more than white tipping or secondary tillering can also be an indication of a Cu deficiency. In conclusion it is essential to have a recent soil / plant analysis report to identify the soil trace element status in order to advise a suitable programme to meet crop micro nutrient requirements.