Addressing Copper Deficiency with SWAT MAPS
Copper deficiency caught CropPro’s eye in 2019 when a client had asked about some brown-gray patches appearing in his cereal field (Figure 1). Interestingly, this field was split in half between oats and wheat, but the patches only appeared in the wheat and on the hilltops (SWAT MAP zones 1-2). We conducted some extra tests and determined the cause of these patches to be copper deficiency. One of the most sensitive crops to copper deficiency is wheat; this explains why the patches were only in the wheat half of the field. Crop sensitivity to copper is wheat, flax, canaryseed > barley, alfalfa > timothy, oat, corn > peas, clover > canola, rye.
What to Look for and Where
When scouting your crops during the growing season, we pay attention to the higher and drier areas of the field (zones 1-2). Copper deficiency tends to show up in soils that are light textured and low in organic matter. Indicators of copper deficiency include uneven crop staging, twisted “pig-tailed” leaves (Figure 2), dead leaf tips, bending of the stem at maturity, and the plant will die off early to become brown-gray in color. Harvest can also help classify a copper deficiency as fusarium, ergot, take-all, empty shriveled heads, and low test weight may occur.
The concern for copper deficiency is when soils reach 0.5 ppm or lower; critical level is once soils start getting around 0.3 ppm. Deficiency is particularly common in sandy soils or peat. Because of this, deficient soils are primarily concentrated throughout the Grey soil zone in Saskatchewan.
In our case study field, we conducted comparative double depth sampling to help us determine what was going on (Figure 3). Samples were taken in the areas showing symptoms (Poor Area; zones 1-2) and in areas of the field that weren’t showing visible symptoms (Good Area; zones 5-7). Comparing the soil sample results, the topsoil from both areas were both low in copper; however, in the subsoil, the poor area was low in copper and the good area had adequate levels. So, the crop in the good areas of the field was able to access copper at depth. The poor looking patches had no access to copper at depth, and so, suffered from copper deficiency. As mentioned earlier, soils that are light in texture and sandy have a higher chance of being copper deficient. Upon review of the soil sample results, the topsoil of the poor area/patches was low in organic matter (OM%) and is even lower in the subsoil – these areas had subsoil sand.
Success with Copper Applications
A response to copper application is not always guaranteed even when soils test below the critical level of copper. But it does mean that there is a higher chance of response. At the same time, there is a lot happening in the top- and subsoil. In the example field mentioned above, the topsoil in both good and poor-looking areas was testing low in copper. Only the areas that looked good had copper at depth. Soil characteristics also play a large part in nutrient-crop interaction and fertilizer responses. For example, if the entire depth of the soil is sandy and/or light textured, there’s a higher probability that a response to copper will occur vs. soil with heavier texture and higher organic matter content. This is because clay soils generally hold more copper in plant available form.
With all of this considered, choosing the right product to help treat copper deficiency is still just as important to ensure the highest probability of a response. Is the form of nutrient being applied readily plant available or does it need to be broken down first? And how much of the actual nutrient is being applied? Sometimes a “Band-aid”, apply every year, strategy may seem cheaper but having to use it every year would add up.
This is in comparison to a long-term strategy where you might apply once to permanently build soil levels, which is more expensive up-front. Logistics may also play a role in choosing the product that best suits your operation.
Fit for VR
If most of the field is not testing below critical levels of copper, then a variable rate application may be a good fit. Longer-term solutions to micronutrient deficiency, like granular products, are more expensive than a “Band-Aid” product. With VR, product application would only be to areas where it is more likely that a response will occur and therefore help in reducing total application costs. Figure 4 shows an example of granular copper being applied using variable rate. Here we placed copper in zones 1-4 and shut it off for the rest of the field. A granular copper trial was done in 2021 on a field of wheat but due to dry conditions, moisture was more of a limiting factor than any specific nutrient(s).
Not every field or area in a field will respond to a copper application. Success with applications depends on the crop being planted, soil characteristics, soil test levels, what form of nutrient you are applying, and the amount of product being applied. Is there a deficiency showing up in the growing season or maybe a chance of one? This should be the starting point. If soil test results for copper come back low but soil characteristics point to a low chance of response, then it may not be worth putting your dollars into a copper application. Utilizing variable rate to apply copper is a good strategy if a response is only likely in certain areas of the field (hills, low OM, light textured soil).