Submitted to: International Conference on Plant Nutrition
Publication Type: Proceedings
Publication Acceptance Date: 6/1/2005
Publication Date: 9/14/2005
Citation: Zhao, D., Reddy, K.R., Starks, P.J. 2005. Assessments of cotton and forage plant nitrogen status using remote sensing. International Conference on Plant Nutrition. p. 1104-1105. Interpretive Summary: Abstract Only.
Technical Abstract: Accurate detection of plant nitrogen (N) status can help growers make appropriate N management decisions. Leaf or plant tissue N concentration is an important indicator of plant N status, but laboratory methods of quantifying N content are costly and time consuming. Non-destructive measurements of leaf or canopy spectral reflectance using remote sensing techniques may provide an alternative means of plant N assessment. Two field experiments were conducted in 2001-2003 using cotton or bermudagrass pastures. The first experiment consisted of four N-rate treatments (0, 56, 112, and 168 kg N ha-1) to determine leaf critical N level associated with cotton yield loss at different growth stages and to select optimum reflectance ratios for estimating leaf N content. Three Bermuda grass pastures were used in the second experiment to determine the relationship between forage N concentration and canopy reflectance. Leaf (cotton) or canopy (forage) reflectance and N concentrations were measured throughout the growing seasons. Cotton leaf N concentration decreased linearly as plants aged and leaf critical N levels resulting in lint yield loss at first square (FS), first flower (FF), 2 wks after FF, and 4 wks after FF stages were 48.9, 40.8, 39.7, and 37.2 g kg-1 DW, respectively. Both cotton leaf N and forage N concentrations linearly correlated with reflectance ratio of R915/R515 or R915/R705. The reflectance ratios might be used for real-time and non-destructive monitoring of plant N status and for N fertilizer recommendation in cotton or for estimating forage quality and adjusting stocking rate in bermudagrass pastures.