|Hunsaker, Douglas - Doug|
|Pinter jr, Paul|
Submitted to: Irrigation Associations Exposition and Technical Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 2/1/2003
Publication Date: 11/18/2003
Citation: Fitzgerald, G.J., Hunsaker, D.J., Barnes, E.M., Clarke, T.R., Lesch, S.M., Roth, R., Pinter Jr, P.J. 2003. Estimating cotton crop water use from multispectral aerial imagery. In Irrigation Associations Exposition and Technical Conference, San Diego, CA, Nov. 18-20. pp.138-148. Interpretive Summary: Current numerical models used for irrigation scheduling rely on single point measurements to predict irrigation needs for entire fields. Precision irrigation requires a measure of the spatial variability inherent in most agricultural fields, but it is not feasible to measure every location in a field to calculate the necessary crop coefficients. The use of remotely sensed imagery could provide the needed spatial information. An approach called, Directed Sampling can provide cost-effective ground "truth" data to relate the remotely sensed imagery to measured plant and soil features allowing statistically robust predictions of other non-sampled locations in the field. Processed aerial imagery of a cotton field acquired on multiple dates during a growing season along with weather station and soil water data were used to produce a seasonal cumulative water use map showing where a cotton crop was deficient in water. Maps such as these could be used by farmers to assist in water management and irrigation scheduling potentially saving water and improving yield.
Technical Abstract: Remote sensing approaches were investigated in Central Arizona for estimating water use by cotton growing in a furrow-irrigated field with considerable soil texture variation. Aerial imagery was obtained every 2-3 weeks using a high resolution, 3-CCD camera system equipped with narrow band-pass filters and calibrated with ground-based reference tarps. The noramlized difference vegatation index (NDVI) was used to estimate basal soil crop coefficients (Kcb) for cotton via a previously defined realtionship. The Kcb plus estimated soil evaporation coefficients were multiplied by reference ET determined from a nearby AZMET weather station and summed during each irrigation interval to provide water use maps. These maps were validataed using the soil water balance with periodic soil moisture measurements. The study demonstrated how maps showing the spatial and temporal dynamics of crop water use can offer insight into effects of soil properties and crop response and help define and manage zones in surface irrigated fields.