Copper for Crop Production

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University of Minnesota as well as other universities has ... grown in Minnesota and their sensitivity to copper fertilization. .... Rochester, 2011. 1.2. 6.1. 6.1. 241.


Copper for Crop Production

Apurba K Sutradhar: Research Associate Daniel E Kaiser, Carl J Rosen, and John A Lamb: Extension Specialists in Nutrient Management Copper (Cu) is one of eight essential plant micronutrients. Copper is required for many enzymatic activities in plants and for chlorophyll and seed production. Deficiency of copper can lead to increased plant susceptibility to disease, one example being ergot which can cause significant yield loss in small grains. Most Minnesota soils supply adequate amount of copper for crop production. However, copper deficiency can occur in high organic matter and sandy soils.

greater concentrations of organic matter. Copper binds with organic matter more tightly than any other of the crop micronutrients. Crops sensitive to copper deficiency grown on peat soils with organic matter content more than 8% are likely to show copper deficiency symptoms.

SOIL TEXTURE: Fine-textured mineral soils

Copper deficiency is more likely to occur in cereal grains in Minnesota when grown on copper deficient soils. Wheat is the most sensitive to copper deficiency. Barley and oat are less sensitive to copper deficiency. Some vegetable crops such as onions, lettuce, and carrots are sensitive to copper deficiency.

generally contain higher amount of available copper compared to sandy-textured and organic or peat soils since fine-textured soils can hold more exchangeable copper. Sandytextured soils are more likely to be copper deficient than loams and clays since parent materials forming sandy-textured soils contain low copper concentrations. Moreover, copper can be leached from sandy soils with low organic matter concentration.


SOIL pH: Soils that contain greater amounts

The amount of copper available to plants varies widely among soils. Copper in the soil is held with clay minerals as a cation (Cu2+) and in association with organic matter. Some silicate minerals and carbonate contain copper as impurities. Research at the University of Minnesota as well as other universities has identified soil conditions where a response to copper fertilizers is expected. These conditions are:

of oxides and carbonates tend to have low available copper. As soil pH increases, the availability of copper decreases. Increasing the soil pH by liming increases the amount of copper held or adsorbed by clay and organic matter, thereby decreasing Cu availability. If crops sensitive to copper deficiency are grown on soils with a pH of7.5 or greater, occasionally check for copper deficiency using soil and plant tissue analysis.

ORGANIC MATTER: Copper is not mobile in organic soils as it is attracted to soil organic matter and clay minerals. Copper deficiencies often occur in soils with peaty soils with

CROPS THAT RESPOND COPPER FERTILIZATION Crops species and cultivars vary considerably in their response to fertilizer-copper. Table 1 lists some agronomic and horticultural crops that respond to fertilizer-copper.

Table 1. Some agronomic and horticultural crops grown in Minnesota and their sensitivity to copper fertilization.

crop. The leaf tips die back and the tips are twisted. Typical deficiency symptoms for wheat are shown in Figure 1 and 2. If copper deficiency is severe, growth of small grains ceases and plants die after reaching the Feekes 3.0 growth stage (tiller formation). Wheat will not produce grain in the head. In mature stands, copper deficiency can be visible by characteristic purplish brown patches, which are signs of melanosis.




Alfalfa, barley, carrot, citrus, lettuce, oat, sugarbeet, wheat, onion, spinach

Apple, blueberry, broccoli, cabbage, cauliflower, corn, cucumber, peas, radish, strawberry, tomato

Canola, dry bean, grape, grasses for hay, potato, rapeseed, rye, soybean

COPPER DEFICIENCY SYMPTOMS Copper deficiency symptoms vary by crops. Copper is relatively immobile in plants and deficiency symptoms first appear in younger plant tissues.

Figure 1. A wheat plant deficient in copper is shown here. The leaf tips die back and they are twisted refer to as “pig tailing”. Photo credit IPNI.

In Minnesota, evidence of copper deficiency has appeared when small grains are grown on organic soils. Copper deficiency symptoms are characterized by a general light green to yellow color in the small grain

Figure 2. Healthy to severely copper deficient wheat heads, showing signs of melanosis. Photo credit IPNI.

Figure 3. Copper deficiency in corn. Photo credit: Michigan State University.

In corn, deficiency first appears on new leaves as they come out of the whorl and develop a bluish green tint (Figure 3). New leaves may emerge from the whorl as spiraled. Necrosis may occur on older leaftips and edges and may die.

In vegetable crops, young leaves may turn bluish-green before turning yellow. Figure 4 shows a lettuce plant affected with severe copper decency. The upper portion of the plant wilts; the growing point is stunted and eventually dies. The plants often fail to flower.

fertilizer program. In Minnesota, copper status of soils can be easily measured by routine soils tests. The DTPA extraction method is used by majority of soil testing laboratories and is the most reliable and accurate for measuring copper in soil. When a soil test indicates the need for copper, small amounts of copper fertilizers can be used in a fertilizer program to provide for optimum yield. Soil test interpretations and fertilizer suggestions to apply copper fertilizer for small grains and vegetable crops grown in organic soils in Minnesota are summarized in Table 2. The suggested interpretation classes of the DTPA copper soil test are only applicable for organic soils and should not be used for mineral soils.

PLANT TISSUE TESTING A deficiency of copper can be confirmed using plant tissue analysis. Plant tissue analysis should be used in conjunction with soil tests before arriving at recommendation for using copper in a fertilizer program. Interpretations for various concentrations of copper in plant tissue of several agronomic and horticultural crops are summarized in Table 3. Tissue copper concentration varies between growth stages. It is important that crops be sampled at the growth stage listed if interpretation of plant analysis is to be accurate.

Figure 4. The plant on the right is showing copper deficiency in lettuce compared to a non-deficient plant on the right. Photo credit: IPNI.

DIAGNOSING COPPER DEFICIENCY Soil and plant tissue tests are recommended to determine copper deficiency in soils. Soil tests may be correlated to plant response for specific soil types.


Soil tests for copper on organic soils are the best predictor of the need for copper in a Table 2. Soil test interpretation and recommendations for copper to be used for small grains production on organic (peat) soils in Minnesota. SOIL TEST COPPER (ppm)†


lb. Cu/ac.


0-2.5 (low) 6-12 24-48 2.6−5.0 (marginal) 6 24 > 5.0 (adequate) 0 0 †Copper is extracted by the DTPA procedure.

lb. Cu/ac.


0.3 0.3 0

1.2 1.2 0

Table 3. Sufficiency levels ofcopper for major agronomic crops, vegetables, and fruits grown in Minnesota. CROP




Alfalfa Apple Blueberry Broccoli Cabbage Carrot Cauliflower Edible bean Field Corn

Prior to flowering 7-30 Tops (6′′ new growth) Leaf from middle of current terminal shoot July 15-August 15 6-25 Young mature leaf First week of harvest 4-10 Young mature leaf Heading 4-15 Half-grown young wrapper leaf Heads 5-15 Young mature leaf Mid-growth 5-15 Young mature leaf Buttoning 4-15 Most recently matured trifoliate Bloom stage 5-30 Whole tops 5-20 Less than 12′′ tall Base of ear Initial silk 6-25 Grape Petiole from young mature leaf Flowering 5-20 Pea Recently mature leaflet First bloom 6-25 Potato Fourth leaf from tip 40-50 days after emergence 5-20 Petiole from fourth leaf to tip 40-50 days after emergence 4-20 Raspberry Leaf 18 inch from tip First week in August 15-60 Soybean Trifoliate leaves Early flowering 21-80 Spring wheat Whole tops As head emerges from boot 15-70 Strawberry Young mature leaf Mid-August 20-50 Sweet corn Ear leaf Tasseling to silk 20-100 Sugar beet Recently matured leaves 50-80 days after planting 10-80 Source: Bryson et al. (2014), Plant Analysis Handbook III; Rosen and Eliason (1996), Nutrient Management for Commercial Fruit and Vegetable Crops in Minnesota.

Table 4. Summary of grain yield of hard red spring wheat as affected by broadcast application of copper fertilizers. COPPER SOURCE


lb./ac. None Copper Sulfate Copper Sulfate Copper Chelate Copper Chelate

-6 12 6 12



NORMAN, 2000


NORMAN, 2001


-----------------------------------------bushels/ac.----------------------------------------66.2 65.7 61.9 64.5 67.8

47.3 50.0 47.8 47.6 51.0

50.4 b† 55.6 a 54.9 a 57.4 a 57.1 a

57.7 57.0 55.5 58.4 55.9

45.2 43.0 47.7 47.9 47.6

† Means in a same column followed by different lower case letters are significantly different at the P > 0.05 levels of probability.

CROP RESPONSE TO COPPER IN MINNESOTA Trials with hard red spring wheat grown on mineral soils have been conducted in northwestern Minnesota. The yield from those trials are summarize in Table 4. The majority of the sites selected for this study in 2000 and in 2001 were sandy with an organic matter concentration of 2.0% or less. Copper fertilization produced an increase in yield of hard red spring wheat only at one site (Norman County 2000). Because of the rarity of a response to copper fertilization on

59.5 58.3 59.6 58.7 60.7

mineral soils, additions of copper to a fertilizer program are not suggested for small grain production on mineral soils in Minnesota. Corn response to copper has not been documented in Minnesota (Table. 5). Corn is only moderately sensitive to copper deficiency. A response to copper may occur when corn is grown on organic or peat soils. Application of copper under these circumstances should be conducted on a trial basis to determine if copper fertilizer application is economical.

Table 5. Summary of corn grain yield (15.5% moisture content) for plots with (+Cu) and without (-Cu) copper fertilization. SITE

Oklee, 2011 Rochester, 2011 Staples, 2011 Westport, 2011 Gaylord, 2012 Montgomery, 2012 Rochester, 2012 Rochester, 2013



ppm 0.2 1.2 0.7 0.6 1.7 2.0 2.0 0.97

% 18.7 6.1 7.1 6.5 6.3 3.1 2.2 2.1

Note: Treatments are not significantly different at P < 0.05 probability levels.




bu/A 6.3 6.1 7.1 6.5 6.4 7.4 5.7 5.8

110 241 197 194 185 195 158 177

113 234 196 195 191 189 154 179

Table 6: Some common Copper fertilizer sources and quantity needed to supply 1 lb Cu/acre. MATERIAL† Copper chelate Cupric ammonium phosphate Cupric chloride Cupric oxide Copper sulfate (monohydrate) Copper sulfate (pentahydrate) Cupric oxide Cuprous oxide


Copper deficiency is rare in soybean. Soybean response to copper has not been verified in Minnesota. Vegetable crops such as onion or carrots are more likely to respond to copper fertilizer on some soils. However, trials have not been conducted in Minnesota to determine the potential for a response to copper for onion or carrot.

FERTILIZER MANAGEMENT Copper sulfate is the preferred source of copper fertilizer because of low cost compared to chelated sources. Some commonly used copper fertilizers are listed in Table 6. Soil application of copper before seeding is most common. Copper fertilizer can be broadcast or banded with nitrogen, phosphorus, and potassium fertilizers. Copper use efficiency is improved if the

APPROXIMATE Cu (%) 13 32 17 75 35 25 75 89


7.7 3.1 5.9 1.3 2.9 4.0 1.3 1.1

fertilizer is water soluble and the particle size of the fertilizer is small. A single application of copper can last for many years. Foliar application of copper can also be an effective way to correct copper deficiency in small grains and vegetable crops. The growth stage and application time has a major influence on the effectiveness of the treatment. Results from research in northwestern Minnesota indicated that applications at the Feekes 3 (tillering) growth stage are most effective in correcting deficiencies. Two applications [one application at Feekes 3 and the other one at Feekes 10 (booting stage)] of foliar copper fertilizer may be required if deficiencies are severe. For vegetable crops, leaf burn has been observed if foliar applications exceed 0.15 lb Cu/A. Two or three foliar applications at weekly intervals are usually

necessary to correct copper deficiency in vegetable crops.

COPPER TOXICITY There is a narrow range between copper deficiency and toxicity. Proper care should be taken during application of copper fertilizer. Repeated application of copper fertilizer, swine and dairy manure, and sewage sludge can develop copper toxicity. Copper toxicity can persist for an extended period of time and is difficult to correct because the low solubility of Cu in water. Toxic concentration of copper in soil affects seed germination, root system development, and plant vigor. Fields that routinely receive fertilizers containing copper and manure require regular monitoring for copper toxicity.

Copper can be broadcast or incorporated before planting and can also be applied as mixtures with other fertilizers. One or two foliar applications are suggested depending on the severity of deficiency between Feekes 3 and Feekes 10 stage of spring wheat grown in Minnesota.

For more information:


Fertilizing with copper is an important consideration when growing small grains on organic (peat) soils in Minnesota. The recommendations listed in Table 2 are for organic (peat) soils only. Yield response to copper when crops are grown on mineral soils (sandy loam, loam, clay loam, etc.) in Minnesota has not been measured, so copper is not recommended for mineral soils.

The soil tests for copper on organic soils and plant tissue tests are reliable determining copper deficiencies and the need for fertilizing with copper.

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