Comparison of Two Active Sensors in Estimating in-Season Plant Nitrogen Status in Irrigated Cotton

Spectral reflectance of crop canopies measured using active sensors is a good estimator of crop biomass and in-season canopy level sensing has the potential to supplement pre-plant soil testing data, by providing information on the need for fertilization.  Thus, field reflectance studies that can assess in-season biomass and plant nitrogen concentration in cotton in gaining much importance with increase in crop input costs.  In the growing seasons of 2007-2009, spectral reflectance indices at I m above the canopy of cotton at early squaring and at mid bloom cotton were measured using both GreenSeeker and CropCircle hand-held active sensors.  Spectral reflectance indices like normalized difference vegetative index (NDVI), near Infrared reflectance (NIR) and visible reflectance (VIS) were correlated with in-season plant measurements like biomass, leaf and total nitrogen uptake