Sensor Based Nitrogen Recommendation (SBNRC) Technology UpdateThu, 26 Jan 2012 14:51:18 CST
For the more than 500,000 acres of winter wheat in Oklahoma that have an N-Rich strip in them, this year the mild winter weather pattern is causing a need to adjust the values inputted into the SBNRC calculator. This current winter has seen an abnormally high number of days with an average daily temperature between 35° and 40° F. This creates an unrealistically high yield potential and faulty nitrogen rate recommendation. This article outlines what is happening to the SBNRC and how to make the correction so that a correct yield potential and N rate is calculated. The adjustment is easily preformed and makes sound agronomic sense.
Man producers have already applied to-dress nitrogen (N), but thousands of acres across Oklahoma are still being evaluated for N need. With N-Rich strips being utilized on more than 500,000 acres, sensors have been recharged and more are hitting the field every day. While sensing strips over Christmas break, I came across an anomaly in the SBNRC recommendations. The calculator was overestimating yield potential (YP). This was either causing N rec to be too high if the max yield entered was not reached or the N rec to be too low if the YP was higher than the Max yield set. This trend has held out consistently across the state.
When speaking about the SBNRC, I try to emphasize that this technology is a tool that should be used in conjunction with sound agronomic application. When I noticed that even when the N-Rich strip was significantly greener than the rest of the field, the SBNRC N recommendation was very low, I knew something was wrong. I looked at the day values, GDD's > 0, the number of growing days was very low considering the size of the plants. GDD’s are very important as they let the calculator determine the time left in the plants’ life cycle. The smaller the GDD, the more time the plant has to grow and produce grain. For the GDD>0 calculation, we look at the average daily temp (Max temp plus Min temp divided by 2) and any time the average daily temperature goes above a critical level that day is counted as a growing day. For wheat we use a critical level of 40 degrees F.
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