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The role of copper in plant nutrition

Copper deficiency in soils has been correlated to lodging in cereal crops, mainly because copper is a nutrient involved in lignification or straw strength, which determines the standability of the plant. Low copper can also cause increased disease, increases in ergot and melanosis, twisted flag leaves and an increase of aborted seeds in the head.

“As well, copper plays an important role in nitrogen utilization,” says Terry Aberhart, an agri-coach with Agri-Trend Agrology Ltd. Aberhart has seen and dealt with copper deficiencies on his own farm in Saskatchewan. “You may see poor nitrogen efficiencies and have a hard time achieving top protein levels if you have issues with copper in your crops.”

Growers aiming for high yields in cereal crops should pay close attention to soil-available copper levels to avoid yield loss, quality loss, delayed maturity and severe crop lodging, which can be due to a copper deficiency sometimes induced by high nitrogen levels.

Copper and lodging

The lodging susceptibility of copper deficient cereal crops due to impaired lignifications of cell walls can be increased by high nitrogen fertilizer rates, says German plant physiologist, Horst Marschner, in his book Mineral Nutrition of Higher Plants.

Other experts are not so sure about the relationship between lodging and copper. “If the lodging is observed on peat or very high organic matter soils, (where copper deficiency is common), the cause of that lodging may also be due to low potassium level of peat soils and high nitrogen release,” says John Heard, crop nutrition specialist with Manitoba Agriculture, Food and Rural Initiatives. “I would suggest that if soils test low in copper with suspect soil conditions (low organic matter, sandy and high pH soils or peat soils) that farmers should fix their copper problem — regardless of any minor effect it has on lodging. But I am not a proponent of copper use on non-deficient soils.”

Harry Brook, crop specialist with Alberta Agriculture and Rural Development is convinced that the problem of lodging is usually more related to potassium levels in prairie soils than copper. “I believe producers should test the hypothesis for themselves by conducting strip trials on their fields. If there is a real deficiency, it should show up in the results at harvest time,” says Brook.

Copper and ergot

Ergot is a disease that often seems to be present when there is significant lodging in cereal crops. Some experts believe that the correlation between the two relates to copper. “If you have poor lignifications and poor pollination (because of copper deficiency), the plant is predisposed to fall over, even though there isn’t much weight in the heads,” says Elston Solberg, president of Agri-Trend Agrology Ltd., who has conducted extensive research into the role of copper in plant development. “The heads are predisposed to stay open for a longer period of time because, even though they are close-pollinated, if they have none of their own pollen, they will keep their heads open for a longer period of time in the hopes of getting pollen from a nearby plant, and that’s when the ergot infection gets in.”

Although Brook acknowledges that copper can sometimes play a role in ergot infection, he believes that weather is more often the biggest contributor to the problem. “Wheat is most susceptible to ergot because it has a period of time when the flowers are mostly open to the outside atmosphere as the head emerges,” he says. “If you get a period where it gets cool and it slows down the development of the wheat, you have the wheat flowers exposed for a longer period of time to any windblown spores or fungus. So (ergot infection) is mostly weather related.”

The important message is that copper deficiency should be correctly diagnosed before copper fertilizer is applied.

Detecting copper deficiency

Some of the main indicators of copper deficiencies in cereal crops are light green leaves and dry leaf tips, with slow and stunted growth. Another symptom that has been observed in copper deficient cereal crops is bending of the stems or heads, which may break 15 to 30 cm below the head.

“The best way for a farmer to know for sure if he has a copper deficiency is to have soil and tissue tests done,” says Aberhart. “Just having a soil test alone will not provide the same level of confidence as having both soil and in season tissue analysis.” If a farmer sees some of these symptoms or feels he is not getting the yields and crop quality he’s striving for, he should get in-depth soil and tissue tests done to determine the extent of the copper issue and develop a strategy to deal with it, he adds.

A wheat crop will take up just over 0.5 grams of copper per bushel, and remove about 0.15 g/bu. from the soil. So a 70 bushel crop will need to find 36 to 37 grams of copper and will remove about 10 grams.

Barley will take up about 0.38 g/bu. and remove about 0.34 g/bu. of copper from the soil. A barley crop will remove almost all of the copper it takes up. A 100 bushel barley crop will need to take up about 38 g/bu. and will remove about 34 g/bu. from the soil.

Oats take up almost the same amount of copper as barley but only remove about 0.18 g/bu., so a 130 bushel per acre oat crop will need to take up about 47 g/bu. of copper and will remove only 23 g/bu. from the soil.

Correcting copper deficiency

Copper can be applied within a seed treatment as a granular application, impregnated on dry fertilizer, in a liquid fertilizer blend or as a foliar treatment.

Copper is not mobile in the soil or in the plant, so placement and timing of products is very important. Most cereal crops have the highest demand for copper uptake in the vegetative and seed development stage. “So that is when you will want to ensure that your crop will be able to get the copper it needs to produce top yields and quality,” says Aberhart.

If only small amounts of copper are required, seed treatments and a foliar application may be sufficient and give the most economical response. “The thing to consider with seed a treatment is that you are applying a very small amount, and that copper will be gone by the time the crop gets to the critical stage,” says Aberhart. “The same is true with a foliar treatment. You are applying a small amount of copper, but it can be very effective if applied at the right time.”

Copper cannot be foliar applied once the head is starting to come out of the boot, as crop damage and reduced yields can occur. Foliar copper can cause some leaf burn to the plant if put on at higher rates and in hot conditions, especially if combined with fungicides, where there are additional surfactants.

Soil-applied copper is effective, but there needs to be good root interception and uptake. If a 20 per cent granular copper product is applied at five lbs./ac., it will result in one lb./ac. (or 454 grams) of actual copper. Depending on the crop and yield, this could provide enough copper for ten or 15 years or crops. “The issue is that you will only have about two or three granules per square foot of soil and will have very low root uptake and interception,” says Aberhart. “This is where applying lower analysis products, impregnation of other dry fertilizers which will increase granular distribution, or adding to a liquid blend can increase your chances and efficiency of uptake with soil applied products.”

There are many factors involved in copper uptake and application for crops. Farmers need to consider soil type, organic matter, copper levels throughout the soil profile (many soils may have poor copper levels at the surface but increases deeper down), pH levels, crop yield and quality, protein goals, and whether they are dealing with soil that they want to build, maintain or mine, says Aberhart.

Copper products

There are hundreds of copper products and application methods with various considerations including efficiency of uptake, timing, solubility of the product, and suitability for soil or foliar application. “Most of our growers that we work with on a copper strategy use a combination of a couple of different products and applications to best suit the needs of the crop and work with the logistics of their operation,” says Aberhart. “There are hundreds of easy, effective, and profitable ways to apply copper to you crops. There are many times we hear from growers that have tried applying copper to their crops with no response. There are two reasons for this, either the crop did not need copper, or they did not use the right product, in the proper manner or timing, as there are many ways you can apply these products and not get the value from them because of this.”

Aberhart suggests that farmers work with someone that can really understand their soils and all the different copper products and methods of application in order to achieve the best results. On his own farm, Aberhart has seen better crop yields, increased standability, reduced disease and ergot issues. “Overall we see better crop quality, more consistent yield and increased grain weight and plumpness especially in barley and oat crops, as well as increased protein levels in our wheat crops,” he says. “In today’s new pricing environments crop quality and protein levels will have a large economic impact on the farms bottom line.”

The debate about the role of copper and whether copper deficiencies have a role in lodging, ergot development or other crop problems could go on forever, but perhaps what’s more important in growing any crop is to think like a plant. What does it need and where is it going to get it? That involves moving away from traditional recipe farming along a continuum that leads to assessing and farming different parts of each field according to their individual requirements, says Solberg.

“There’s no better example than copper,” he says. “The variability of copper is so huge sometimes that only 30 per cent of the field may be affected by the copper deficiency. That’s where you see the lodging and the predominance of the ergot and all those other issues that are associated with copper deficiency. So it’s really important to collect information and act on that information in a logical and scientific manner.”

A proper crop planning system with a good soil and tissues testing program means that farmers can consistently track yields, quality, soil and plant levels every year to make sure they get the best economic benefit to their bottom line, says Aberhart. †

About the author

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Angela Lovell

Angela Lovell is a freelance writer based in Manitou, Manitoba. Visit her website at http://alovell.ca or follow her on Twitter @angelalovell10.

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