Effect of Irradiance on Chlorophyll Estimation with the Minolta SPAD-502 Leaf Chlorophyll Meter

Leaf chlorophyll content may be used as an indirect indicator of crop nitrogen status. Chlorophyll meter values (SPAD values) taken with the Minolta SPAD-502 chlorophyll meter in the shade plantOxalis acetosellaL. and in winter wheat (Triticum aestivumL.) varied by 15 and 8%, respectively, with variation in irradiance. The lowest SPAD-values were measured at high irradiance. During a natural night-day-night cycle SPAD values for winter wheat were lowest in the middle of the day, highest at low irradiance at dusk and dawn and intermediate in darkness before dawn and after dusk. The results indicate that irradiance during measurement should be considered when using the Minolta SPAD-502 chlorophyll meter for the estimation of crop N-status.