Effect of water stress on chlorophyll meter readings in winter wheat

Abstract

Chlorophyll and nitrogen (N) are intimately linked in plants, and there is much interest in using chlorophyll as a surrogate for diagnosing crop N status. This is mainly due to the ease with which chlorophyll can be estimated with devices such as the Minolta SPAD meter. However, factors other than N can influence growth/chlorophyll/N relationships, and hence the interpretation of SPAD meter readings. The aim of the present study was to see how water stress affected critical SPAD meter readings for maximum growth of winter wheat. Winter wheat was grown under controlled conditions in sand culture to the 6-leaf stage, with 7 rates of N (deficient to luxury) and 2 water regimes (stressed and non-stressed). Water stress was achieved by adding polyethylene glycol (PEG) to the nutrient solution. Nitrogen and water stress reduced plant growth, but maximum growth was attained at the same N supply irrespective of water supply. SPAD readings were highly correlated with leaf chlorophyll and N. The best and most universal calibration, independent of water supply, was with N concentration expressed on a leaf area basis. Critical SPAD values for maximum shoot growth were 53 and 44 at low and high water supply, respectively.