Have you ever had a wheat crop that had yellow, twisted leaves? Or a canola crop that was pale green, thin, and had small leaves?
These cases are examples of nutrient deficiency which have the potential to cause significant yield losses. In the examples above, the wheat crop would be suffering from copper deficiency and the canola would have a phosphate deficiency. Different nutrient deficiencies affect plants in different ways because the nutrients are often required for several different functions within the plant. Also, interactions between different nutrients and ratios of nutrients (i.e. nutrient balances) can cause physiological problems for the crop. Even slight nutrient deficiencies or imbalances that don’t have visual symptoms can cause yield losses.
The best way to prevent any nutrient problems in-season is to soil test and have a fertilizer recommendation prepared by a qualified agronomist. Most soil testing takes place as composite samples from two soil depths, 0-6 inches and 6-12 inches. Grid sampling is another method of sampling which takes samples in a grid pattern across a field and tries to account for more irregularities in the soil; this is a much more intensive method of sampling and is the method used in Cavalier Agrow’s iFARM (Intelligent Fertility Analysis Rate Management) program. The soil test will give an indication of what nutrients are present in the soil and at what concentrations, cation exchange capacity (CEC), organic matter content, and pH. CEC, organic matter, and pH are important to note as they affect the availability of some nutrients to plants. From the soil test report, an agronomist can provide a balanced fertilizer recommendation that takes into account various soil properties and the nutrient balance already present in the soil.
But you missed out on soil testing for the following year. What can you do?
Regular scouting and tissue testing can give you an indication of how your cropis managing. Symptoms of nutrient deficiency appear in different parts of the plant depending on what nutrient is limiting. For example, nitrogen deficiency will appear in the oldest or lower leaves of the plant as yellowing or chlorosis, and sulfur deficiency will have similar yellowing in the youngest or top leaves. Some nutrient deficiencies have very striking symptoms which can be easily seen, such as copper deficiency. However, it may be too late to apply a foliar nutrition product to relive the deficiency by the time those symptoms appear. Tissue testing allows for an update on the crops’ nutritional status and can give an indication of a deficiency even before symptoms appear. In this case, nutrients can be top-dressed or foliar-applied to supplement the crop before significant yield losses occur.
When and how often should I test my soil and crop?
Soil testing should be done every year at the same time of year to receive consistent results, either in the spring or fall. Testing should especially occur after large or small yields come off and after extreme weather events. Some nutrients move with water in the soil profile (such as nitrate-nitrogen, sulfur, and boron) and their concentration can vary significantly from year to year. Immobile nutrients will not move significantly but it is important to keep any eye on the amount of nutrients that are being removed from the soil to prevent soil mining. Tissue testing should occur in conjunction with soil testing. This allows a comparison between what nutrients are available in the soil and what the plant is actually taking up. Testing should occur 3-4 days before herbicide application in wheat and peas, and 3-4 days before the second herbicide application in canola. This will give enough time to receive the results of the tissue test and determine which nutrient(s) are limiting as the turnaround time on tissue tests is quite quick.
If you have any questions about soil or tissue testing or the iFARM program, please contact your local Cavalier Agrow business agronomist.