|Hunsaker, Douglas - Doug
|BARNES, EDWARD - COTTON INC, CARY NC
|ROTH, ROBERT - MARICOPA AG CTR AZ
|Pinter Jr, Paul
Submitted to: Proceedings of the World Water and Environmental Resources Congress
Publication Type: Proceedings
Publication Acceptance Date: 4/1/2005
Publication Date: 7/14/2005
Citation: Fitzgerald, G.J., Hunsaker, D.J., Barnes, E.M., Clarke, T.R., Roth, R., Pinter Jr, P.J. 2005. Estimating cotton crop water use from multispectral aerial imagery, 2003. Proceedings of the World Water and Environmental Resources CongressMay 15-19, 2005, Anchorage, Alaska, USA. p. 525/pdf.
Interpretive Summary: Efficient use of irrigation water requires that the timing and amount of irrigation be matched to crop needs. However, fields can be highly variable in soil type and other factors that affect crop water use, and it is not feasible to measure every location in a field to calculate crop water requirements. The use of remotely-sensed imagery could provide the needed spatial information. If a relationship can be developed between the imagery and the crop's water need, then imagery of a field can be transformed into water use maps. In this study, aerial imagery of a cotton field was acquired on multiple dates during a growing season along with weather station and soil water data. Using a previously-defined relationship between the imagery and the crop's water needs, a seasonal cumulative water use map was produced showing the water use patterns for a cotton field. Maps such as these could be used by farmers to assist in water management and irrigation scheduling, potentialy saving water and improving yeild.
Technical Abstract: Current numerical models used for irrigation scheduing rely on single point measurements to predict irrigation needs for entire fields. To incorporate the spatial dimension, remotely-sensed imagery was investigated as a tool for estimating water use by cotton in central Arizona. This report presents the second year of a study situated in a furrow-irrigated field with large variation in soil texture. Aerial imagery was obtained every two to three weeks using a high resolution camera system equipped with narrow band-pass filters and calibrated with ground-based reference tarps. The normalized difference vegetation index (NDVI) was used to estimate the crop coefficient (Kcb) for cotton via a previously defined relationship. The Kcb plus estimated soil evaporation coefficients were multiplied by reference evapotranspiration (ETo) determined from a nearby weather station and summed during each irrigation interval to provide a seasonal water use map of the field. The map was validated using soil water balance with periodic soil moisture measurements. Areas of the field with less vigorous canopy were poorly predicted in 2003, although ET in areas with more robust growth was well characterized. Although ET predictions in 2003 were not as accurate as in 2002, the study demontrated that if relationships between imagery and ET can be developed, maps showing the spatial and temporal dynamics of crop water use can be created. Water use maps can offer insight in spatially-variable crop reponse and help define and manage zones in surface irrigated fields.