By: Ken Panchuk, PAg - Provincial Specialist Soils
When scouting, look for yellowing of the lower, older leaves, and if the crop is a bit pale green to slight yellow, check your records to see if the rate of nitrogen may have been a little too low for the good growing conditions. If you see the typical nitrogen deficiency symptoms, this may indicate that there will not be enough nitrogen to achieve the yield or protein potential. Be aware that the lower leaves of cereals do die back normally too and that this is not a sign of nitrogen deficiency.
What to do if you have a crop that is low on nitrogen? Consider top dressing liquid nitrogen with or without a urease inhibitor, depending on when a rain is expected. The rate of nitrogen needed will depend on how much more yield and/or protein potential there may be. Generally a nitrogen top-up application can be from 20 to 40 pounds of actual nitrogen. Use drop tubes or split nozzles to apply these high rates so that the drops are large and roll off the leaves, minimizing leaf burn. Use a urease inhibitor if there is no rain in the forecast within a day or two. Remember, rain is still needed to move the nitrogen into the soil for crop root uptake and the amount of nitrogen taken up by the leaves will generally be small.
Crop scouts do have several tests that can help them determine if more nitrogen is required. Tissue testing is an effective tool. Get instructions from your soil testing lab on how to collect and submit tissue samples. An example of a tool that provides real-time feedback is the hand-held Greenseeker. This will allow comparisons of various areas within a field to get a snapshot of whether top-up nitrogen is needed. However, you do need a healthy area of crop, in the same field, to provide a benchmark for using the hand-held Greenseeker.