Using Ag Weather to Guide Sensor Timing

Using Agweather to Guide Sensor Timing

Robert L. Woods

About this time last year Gage Milliman, Extension Agriculture Educator in Nowata County, took multiple sensor readings on nitrogen ramps in several of Scotty Herriman’s wheat fields.  He reported that nitrogen recommendations for fields that had accumulated 80 GDD’s (growing degree days) since planting, remained close to the same on a subsequent readings taken approximately one week later.  Using the Growing Degree Day > 0 map option, available on the Agweather website you can see that at the time of this newsletter, sensing with the GreenSeeker hand held sensors could begin now on wheat planted before October 5 and south of Wagoner County. http://www.agweather.mesonet.org/crops/default.html

Ideally, topdress nitrogen applications should be applied early enough to allow a rainfall to carry the nitrogen into the soil before stem elongation (jointing) begins or growth stage 6 on the feekes scale.  Sensor readings using the handheld sensors should be taken at growth stage 4 or 5.  Using the Agweather website again, first hollow stem predicted option; you can see that jointing this year is predicted to occur about March 5 in the southern portions of the district or March 10 if you are located in the northern parts of northeast Oklahoma.  Dr. Jeff Edwards, State Extension Small Grains Specialist, says that this prediction tool provides a good estimate but still needs to be ground truthed by actually checking fields and slicing a few stems.  This suggests that we can wait another 2 weeks if necessary to accumulate GDD’s on later planted wheat to get a reliable N rate recommendation using GreenSeeker technology and still get nitrogen applied ahead of jointing.