Nitrogen Use Efficiency, Nitrogen Fertilizers, NUE, Nitrogen and the Environment Cotton Research
Collaborative Sensor Based N Rate Fertilization Project                          Quick links:  
Cotton N Algorithm

$RI = ($RichStrip/$FarmerPractice);
$YP0 = (236.0*exp(2216.2*$NewFarmerPractice/$Gdd))
$YPNRS = (236.0*exp(2216.2*$NewRichStrip/$Gdd))
$RI = ($RichStrip/$FarmerPractice)*1.8579 - 0.932;
if ($RI<1) $RI=1;
$YPN = $YP0*$RI;
if ($YP0>$MaxYield) $YP0=$MaxYield;
if ($YPN>$MaxYield) $YPN=$MaxYield;
if ($YPNRS>$MaxYield) $YPNRS=$MaxYield;
$NRate = ((($YPN-$YP0)*$CRate2)*0.08637/0.5);

Relationship between the response index measured in season, (NDVI of fertilized plot / NDVI of check plot) from readings of cotton at growth stages from 60 to 80 days after planting, and measured lint yield and the response index measured at harvest (yield of fertilized plot / yield of check plot) from all site years.

Relationship between in season estimate of yield (Cum INSEY) computed from NDVI readings of cotton at growth stages from square to peak bloom (800-1300 Cumm GDD), divided by the number of days of planting to sensing, and measured lint yield from all site years.  Where YP0 = yield potential; YP0 calculated = the mean + one standard deviation. 

Facts and Figures
     95% sufficiency: N rate switch
         200 Julian days (mid bloom)
         What is the latest date N can be applied and where you can still produce maximum yields
         Can you catch up if you apply at mid bloom?
         After 1st open boll, leaves start to drop
         Ramp Calibration Strip:  can use to avoid rank growth
         5 weeks beyond S-square is the latest time to apply N?

Cotton plant height collected by hand versus plant height measured using a sonar device.  Ninety three percent of the variation in plant height could be explained using this indirect method of measurement.

                                                    N fertilization Experiment

                    Trimble Pocket Sensor, Greenseeker, NDVI, nitrogen