Copper Deficiency in Cereal Crops

Adapted from Agdex 532-2. Revised June 1995
[Characteristics of copper deficient soils] [Copper's role in plant growth]
[Copper deficiency symptoms][Soil tests for diagnosis of copper deficiency]
[Copper fertilizers]


Introduction

Copper is an essential nutrient needed for the normal growth and development of cereal crops. Copper is removed in the grain of cereal crops at the rate of 0.05 lb./ac/yr compared to 10 to 100 lb./ac/yr for major nutrients such as nitrogen, phosphate, potash and sulphur. If straw is taken from a field an additional 0.02 to 0.04 lb./ac of copper may be removed.

Organic (peat) soils are very prone to copper deficiency. In Western Canada, research has shown that organic soils deeper than 45 cm (18 inches) often respond dramatically to copper fertilization. Marginal to severe copper deficiency has been conclusively identified on mineral soils in the Black, Gray-Black and Dark Brown soil zones of Alberta. The extent of the deficiencies on these soils is not well defined but at least 3 million acres are estimated to be affected.

The visual symptoms and diagnostic guides provided here will help producers to identify copper deficient fields. Copper deficiency should be correctly diagnosed before copper fertilizer is applied. On deficient soils, symptoms generally occur in irregular patches. Deficiency is often first noticed on wheat as "stem melanosis". This is a browning discoloration of wheat associated with reduced yields and ergot infestations.

Characteristics of copper deficient soils

Copper deficient soils have several characteristics related to texture, organic matter and soil pH that indicate where a deficiency will likely occur. 
Texture: 
Deep sandy and light loamy easily worked soils are more prone to copper deficiency than medium and heavy textured clay-type soils. 
Organic matter: 
Copper is strongly bound to organic matter. Peat soils and mineral soils with high levels of organic matter (6-10%) are most likely to be deficient in plant available copper. Livestock manure and residues from the previous crop also influences soil copper availability. 
Soil pH: 
Copper availability is reduced as pH increases to 7 and above. However, copper deficient mineral soils in Alberta typically have a pH that range from 5.8 to 6.8. 
Other soil nutrients: 
High nitrogen levels delay the translocation of copper from older leaves to the growing points (i.e., head development), significantly enhancing copper deficiency). High levels of phosphorous, zinc, iron, manganese and aluminum may also restrict copper absorption by cereal roots. 
Farmers that observe copper deficiencies are almost always managers striving for optimal yields. Their fertility management often includes manure and above average rates of fertilizer application. In many instances, their first indication of copper deficiency are crops with yield and quality consistently below expectations.

Copper's role in plant growth

Chlorophyll production, protein synthesis and respiration are important plant functions that need copper. About 70 per cent of the copper in plants is found in the chlorophyll. A copper deficiency can result in early aging or lowered levels of chlorophyll, which leads to yield reductions that go unnoticed if the deficiency is not severe.

Cereal species vary in their sensitivity to copper deficiency. The usual order of sensitivity (response) is: winter wheat > spring wheat > barley > oats > triticale > rye. Rye can extract up to twice as much copper from the soil as wheat grown under similar conditions. In addition, differences in tolerance to low copper from one variety to another, particularly of barley and oats, can be as great as the differences from one crop species to another.

Canola has yet to be observed to respond to the addition of copper to the soil, whereas flax is very responsive.

Reasons for genetic differences in copper sensitivity include: 

  • lower tissue requirements for copper, 
  • different rates of absorption of copper by the roots, 
  • more efficient transfer of copper from roots to foliage, 
  • better exploration and root contact with the soil.

Copper deficiency symptoms

Copper deficiency in cereals produces characteristic symptoms that may be similar for each species. However, crops growing on marginally copper deficient soils may have losses of 20 per cent or more in grain yield while not showing visual symptoms of a deficiency. Visual symptoms of copper deficiency are commonly observed in fields of wheat, barley and occasionally oats in central and northern Alberta. Many of these symptoms may be confused with frost damage, insect damage, diseases and herbicide injury. Some herbicide/cereal interactions have been documented on copper deficient soils.
 
  Degree of deficiency
Symptoms  Slight Moderate Severe
Limpness or wilting at mid-tillering. x
Limpness or wilting at stem elongation.  x
Pale yellow, curled young leaves at tillering. x
Pigtail - The leaf tip dies and may roll and turn white, sometimes appearing fibrous. Upper one-third or half of the leaf may wither and break abruptly at the healthy part. x x
Increased susceptibility to disease. x x
The presence of ergots in the grain heads, specifically wheat and barley. x x x
Unusually high levels of take-all or "fake-all" like symptoms, particularly in 0slo wheat. x x x
Retarded stem elongation.  x x
Excessive late tillering and high mortality on late tillers. x x
Delay in heading - Non-uniform heading occurs, particularly on light loamy soils where crop emergence and early development is uniform.  x x
Aborted heads and spikelets. x
Heads and spikes are nearly normal, but contain many spikelets that are devoid of grain. Anthesis is poor and late. Grain appears shrivelled and the endosperm is blackened. x x
Delay in maturity and senescence - Maturity may be delayed for several weeks.  x x x
Head and stem bending - Stem may break 15 to 30 cm below the head. x x
Stem melanosis - Dark brown patches out in wheat fields (particularly in Park wheat) that begin to appear at the milky ripe stage. The stems immediately below the head and lower nodes turn dark brown. The head becomes bleached and then turns dirty gray with empty florets and shrivelled kernels.  x x x
Probable loss in grain yield (%).  5-20 20-50 50-100
Probable loss in straw yield (%). Nil 0-10 10-20

Soil tests for diagnosis of copper deficiency

Soil samples must be taken to determine if copper is responsible for poor yield. Soil samples should be taken from both affected and unaffected areas from the 0-6", 6-12" and 12-24" depths. 

Soil samples

Soil test criteria for diagnosing copper deficiency are shown in Table 4. When soil tests are in the marginal ranges, crops should be carefully observed for signs of copper deficiency and copper fertilization tried on test strips. Soils with a history of heavy manure applications may be extremely deficient in copper when the soil test is below 0.6 ppm.

Table 4. Soil copper levels for deficiency diagnosis (0-6 in. depth) of mineral soils.

less than 0.4 ppm* deficient
0.4 - 0.6 ppm* marginal
0.6 - 1 ppm* deficient in some instances
<1.0 ppm usually adequate
* DTPA extractable
Soil copper profiles that remain low or decrease with depth will have a much higher probability of responding to solutions of copper fertilizer than a soil which has soil copper levels that increase with depth (see Table 5).

Table 5. Soil copper profiles. (ppm Cu)

  Probability of Response
Depth High Low
0 to 6 inches 0.5 0.4
6 to 12 inches 0.4 1.2
12 to 24 inches 0.4 2.8
Copper deficiency may exist in the top 6" of soil and yet be adequate in deeper layers. However, in wet seasons, cereal crops may exhibit severe deficiency due to shallow rooting. Normal cereal growth may occur in "dry" seasons.

Copper fertilizers

Both soil and foliar applications of copper fertilizer are effective for overcoming copper deficiencies. Soil applications are more common because a single application can be effective for many years. A foliar application will correct a deficiency if applied during the late tillering stage.
 
 

Table 7. Park wheat response to copper fertilization near Tofield, Alberta.*

  Method of
copper application
Yield bu/acre
3 yr. Avg.
Control 44
Copper chelate soil spray  59
Copper sulphate seed-row 56
Copper sulphate band 50
Copper sulphate broadcast 60
*One-time application of Cu chelate (1 lb. Cu/acre as Cu-EDTA) and Cu sulphate (3 lb. Cu/acre as Cu sulphate).
Foliar applications are most effective and immediate at the late tillering stage. If the deficiency is severe, two applications (mid-tillering and early boot stage) may be required. A copper deficiency may reappear at the head filling stage after early foliar applications. Yield response may not occur to copper fertilizers when they are first applied if the subsequent growing season is dry. Copper does not move in the soil and may remain in the dry surface layers.

Copper sulphate

Copper sulphate, also known as bluestone, is generally the least expensive source of copper. It contains 25 per cent copper and should be broadcast and incorporated into the soil at rates of 10 to 40 pounds per acre (2.5 to 10 lb./ac of copper). These application rates have been effective for at least 10-15 years in Australia. Copper sulphate is available as a fine or coarse crystallized material. It tends to accumulate moisture and is difficult to blend with other fertilizers. Granular herbicide applicators have been used with some success for direct application of copper sulphate.

Copper sulphate can also be dissolved in water and sprayed on the soil surface or as a foliar application. A 2 per cent solution, sometimes buffered with calcium hydroxide, is used for foliar application. Foliar application rates range from 0.1 to 0.3 lb./acre actual copper.

Caution: Copper sulphate is highly corrosive when it comes into contact with metals. Stainless steel and plastic components are required on fertilizer applicators and sprayers. Copper sulphate dust can severely irritate the eyes, lungs and skin.

Copper chelates

Copper chelate solutions contain 5 to 7.5 per cent copper for soil and foliar application. For soil application, copper chelates are applied at about 10 per cent of the rate of copper sulphate but the period of residual response is much shorter. The rates for foliar applications are similar to those for copper sulphate. There are several manufacturers of liquid copper chelates. Chelated copper is also available in a granular form. When using this source, at least 1 lb. of copper should be applied per acre.

Granular copper fertilizers

Micro Blue is a nitrogen, phosphate, sulphur fertilizer (18-2-0-22-3) with 3 per cent copper specifically developed for copper deficient soils by Sherritt Inc. of Edmonton.

Tiger Copper 15/10 is a granular product developed by Tiger Resources of Calgary. This non-corrosive product is blendable with fertilizers and contains 15 per cent copper and 10 per cent zinc.
 
 

Table 8. Responses of various crops to copper fertilizer on copper-deficient soils

Crop Response
Wheat  High
Flax High
Canary seed  High
Barley  Medium-high
Alfalfa  Medium-high
Timothy seed  Medium
Oats  Medium
Corn Medium
Peas  Low-medium
Clovers  Low-medium
Canola  Low
Rye Low
Forage grasses (hay) Low
Source: Department of Soil Science, Faculty of Agriculture, University of Manitoba
http://www.bcwines.com/newpage5.htm

Prepared by:
Elston Solberg, Ieuan Evans,
Doug Penny and Denise Maurice
Plant Industry Division 
Alberta Agriculture, Food and Rural Development