“…Studies utilizing spectroscopy to monitor lettuce condition have been explored in a wide range of stressors. For example, Woodhouse, Heeb, Berry, Hoshizaki, and Wood () showed the potential of this technique for monitoring health conditions of excised leaves of lettuce grown hydroponically under different stress conditions (i.e., copper, zinc, nitrogen, phosphorus, potassium, drought), applied singularly. More recently, studies have focused on the determination of nitrogen content of lettuce leaves and canopy by spectra using multivariate modeling methods (Gao, Mao, & Zhang, ; Itoh et al, ; Mao, Gao, Zhang, & Kumi, ; Sun et al, ).…”