Copper is important for proper plant growth, particularly in alfalfa, wheat and soybeans. But plants only need a small amount. You can prevent copper deficiencies for many years with a single application of two to five pounds per acre.
Plants, especially cereals, need copper for proper formation and growth. Copper is an important part of proteins that regulate biochemical reactions within the plant. Without these proteins and reactions, the crop would fail to grow. Copper also promotes proper seed production and formation, and aids in forming chlorophyll and cell walls and in transporting electrons.
Cereal crops are easily susceptible to copper deficiency and can show many warning signs. Watch for dieback of twigs and stems, yellow or pale green leaves that wither easily, and curled leaves at tillering. Later in the season, cereals deficient in copper may have shrivelled grain, delayed maturity, and bent heads and stems. Copper deficiency can also cause prolonged flowering and heads to fill poorly. These symptoms will appear in patches in the field, similar to what you might see in a drought. In areas of copper deficiency, root rot and stem and head melanosis are common. Areas of copper deficiency can also have a higher incidence of ergot.
WHAT CAUSES DEFICIENCY?
Soil type and pH are more important factors than tillage and other producer-influenced factors. Copper is immobile in the soil. High phosphorus content in the soil can depress a root system’s ability to absorb copper, which can cause a deficiency. Sandy soils in the Grey Wooden and Black soil zones along with peaty soils have a greater chance of being deficient in copper.
Copper is attracted to clay particles as well as the organic matter in the soil. The more clay and organic matter, the more copper that can be in the soil.
Soil acidity improves a plant’s ability to access copper. Availability of copper increases greatly with each unit decrease in soil pH. (Lower pH means higher acidity.)
You can test for copper deficiency with soil or plant tissue analysis. On fields where you may suspect copper deficiency, fertilize a test strip with copper sulphate. Monitor results to see if you notice an obvious yield improvement.
HOW TO APPLY COPPER
You can apply copper in granular form or sprayed in solution. When larger amounts are needed, it is best to broadcast the copper and then incorporate it into the soil with tillage. But with this method, it is very difficult to see the results in the same year. This type of correction will fix a copper deficiency for many years.
For amounts under two pounds an acre, try a surface application followed by soil integration. You can also side band or seed-place a liquid copper solution at 0.25 to 0.5 pounds an acre. Finally, you can give the growing crop a foliar application. This can correct small deficiencies that only affect susceptible crops such as wheat or barley. If the deficiency continues. more than one foliar application will be needed.
Copper sulphate is the most common form used to correct deficiencies. The sulphate version releases more quickly and is more accessible to plants than the oxide version.
The best time for in-crop application is after the first node is visible and before the flag leaf stage. Copper sulphate should not be blended with other fertilizers as it easily absorbs moisture. Also note that copper sulphate can be corrosive to application equipment.
Jay Peterson farms near Frontier, Sask. He graduated from University of Saskatchewan in 2008 with a Bachelor of Science in Agribusiness.