![Sample our Environment & Agriculture journals, sign in here to start your access, latest two full volumes FREE to you for 14 days]({"type":"image" , "src" : "/sda/5934/TOC-Subject-Sample-2021-Environment-Agriculture.jpg"})
Abstract
As water availability is getting more limited, practical tools are needed to make timely decisions on the need to initiate irrigation. Therefore, we investigated if the reflectance vegetation index (RVI) obtained from remote sensing of the crop during soil drying, compared with a fully watered plot as a reference could be used as such a tool for detection of water stress. RVI was measured as green crop area index (CAI) and increased from 1 to 4 during the early vegetative stage of growth. RVI was calculated from incoming (PARi) and reflected (PARc) photosynthetically active radiation and from incoming (NIi) and reflected (NIc) near infrared radiation using the equation RVI=(NIc/NIi)/ (PARc/PARi). The effect of soil drying on leaf expansion, biomass accumulation, abscisic acid (ABA) in xylem sap, leaf water potential and leaf nitrogen content were followed as drought indicators in maize (Zea mays L.) grown in lysimeters in the field. Five to seven days after the onset of soil drying RVI started to decrease in droughted plants when xylem [ABA] increased. Leaf nitrogen content of upper leaves decreased five to ten days after the onset of soil drying. Not until 20 days after onset of soil drying when relative available soil water (RASW) was 20%, did midday leaf water potential (ψleaf) of droughted plants significantly decrease below ψleaf of fully irrigated plants. RVI was highly correlated with green crop area index (CAI) (R2=0.84) and biomass accumulation (R2=0.88). We suggest that measurements of RVI of droughted field plants related to RVI of fully irrigated reference plants within the same field can be used as an early warning system of water stress for irrigation, and hence the need during the early vegetative growth stages in maize.
Acknowledgments
This research was partly funded by the Asian Development Bank through a postgraduate stipend from the Directorate General of Higher Education of Indonesia to Andi Bahrun and partly by the Danish Research Council (SJVF) grant no. 9600971. Excellent technical assistance of J. Thage, B. Skov, and J. Christensen is gratefully acknowledged. We thank Dr. Steven Quarrie, John Innes Centre, UK, for providing us with the antibody to ABA. We are grateful to Dr. Ian Henson for carefully reviewing the manuscript.