By Ken Panchuk, PAg, Provincial Specialist Soils, Regina
Before applying more nitrogen, the first information needed is to determine how much high-grade, high-protein bread wheat and durum is available and the amount of low-protein wheat that is in need of high protein for blending. So far, the 2018 Kansas wheat harvest is reporting protein in the range of 10 to 15 per cent. Having high grades and high-protein wheat and durum on hand will help capture more value from the marketplace.
The next step is to assess whether the nitrogen applied, plus the soil test nitrogen, is enough to meet the yield and quality under the present weather conditions. Is there adequate soil moisture reserve to carry the crop between rainfall events? If there has been enough rain to provide a soil moisture buffer and for a higher realistic yield, then topdressing additional nitrogen may make economic sense.
Dribble banding, with drop tubes or split nozzles, using liquid urea ammonium nitrate (UAN) with or without a urease inhibitor at a suitable rate of nitrogen of about 20 to 40 lbs N/acre at earlier growth stages of wheat will contribute to both yield and protein. At these rates of nitrogen, expect some leaf burn where the nitrogen droplets stay on the leaves. Avoid applying nitrogen during the flowering stage to prevent damage to the florets. Application into the evening up until the heat of the next day may help minimize leaf burn. Applying this rate at later stages of growth contributes more to protein content. Rain is needed after application to move the droplets of liquid nitrogen into the soil for access by the crop roots. If there is no rain in the forecast for a few days, use a urease inhibitor to help reduce the loss of the urea fraction of UAN while waiting for the next rain event.
Several tools are available to help assess fields and to determine whether to apply additional top-up nitrogen. Field scouting is a must, and this can be accomplished by several methods, such as tissue sampling of both good and lighter green areas of fields. Quicker methods such as using optical sensors including hand held or in real-time on a high clearance field sprayer with drop tubes or split nozzles for nitrogen application, or real time drone or satellite images are other options.
Nitrogen is mobile within the plant, so the first symptoms of nitrogen deficiency will appear on the older leaves. Yellowing or pale green of these older, bottom leaves is an indicator of possible nitrogen shortage. Yellowing of the older leaves, usually seen in patches, can be caused by other stresses such as lack of moisture, a soil problem, an imbalance of nutrients, a disease, or even normal senescence.