Nitrogen testing and field strips aid fertilizer applications
Our typical nitrogen (N) recommendation for wheat is 2 pounds N per expected bushel of grain. Long-term data indicates that, on average, this is the correct rate. However, this average is too high a third of the time, too low a third of the time and about right the remaining third of the time. How does one know when the rate is correct? More importantly, how does one know before the N is applied?
Enter the GreenSeeker® sensor technology, developed by Oklahoma State University and now available through all Oklahoma Extension Agents. Using reflected red light, this device optically measures the greenness of plants in a strip in the field with a very high N rate versus plants in the rest of the field. Calculations can then be performed over the Internet to calculate the top-dress Nrate that will give the optimum response. The process is fairly simple. First, apply some of the total Nfor the expected wheat crop in the fall. For this example, assume that 80 pounds of N/acre are normally applied in the fall and 60 pounds are top-dressed in February. Instead, apply less N in the fall, say 40 to 60 pounds N/acre, but also apply a strip across the field with a very high rate of N - perhaps 100 pounds of N/acre in a strip on top of the 40-60 pounds. This gives a N-rich strip where the application rate is high enough to achieve the maximum potential yield. Continue treating the field as you normally would during the winter. The field can be grazed, but the cattle need to be pulled off or fenced out at least two weeks prior to an evaluation in February.
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