Wheat Irrigation Management Using Multispectral Crop Coefficients: I. Crop Evapotranspiration Prediction

Abstract

A method widely used for irrigation management determines crop evapotranspiration (ET c) from reference evapotranspiration (ET o) calculations and estimated crop coefficients. However, standard time-based crop coefficients may fail to represent the actual crop water use, for example, when deviations in weather or agronomic constraints appreciably change crop development patterns from typical conditions. In this study, the FAO-56 dual crop coefficient procedures were applied during experiments with wheat to calculate the estimated ET c for irrigation scheduling. The objective of this research was to determine whether basal crop coefficients (K cb) determined from a normalized difference vegetation index (NDVI treatment) improve the prediction of ET c over a standard application with a locally developed time-based K cb curve (FAO treatment). The experiments conducted for two seasons in central Arizona included subtreatments, equally replicated within the NDVI and FAO treatments, of three plant densities (typical, dense, and sparse) and two nitrogen levels (high and low) to provide a range of crop development and water use conditions. The effects of plant density and N level resulted in significant differences in measured seasonal ET c. Large variations that occurred in the observed K cb and ET c trends between subtreatments were better correlated with the NDVI than the FAO treatment. The mean absolute percent difference for predicted ET c was significantly smaller for NDVI than FAO during both seasons. The treatment difference was 5% for the first season, but 10% for the second season when an unexpected early decline in ET c and K cb was effectively predicted by the NDVI treatment but not by the FAO treatment. NDVI appears to be a robust approach for K cb estimation of wheat, able to reliably predict actual ET c for both typical and abnormal water use conditions.

Estimation of Actual Crop Coefficients Using Remotely Sensed Vegetation Indices and Soil Water Balance Modelled Data

“…Kcb NDVI values for the development growth stage ranged between 0.25 and 0.91 (Table 6), which refer to values commonly accepted [1]. The actual Kcb mid NDVI = 0.87 (Table 6) is lower than the standard Kcb = 1.10 proposed by Allen et al [1] and values obtained for crops with similar canopy [30,31,61]. This is likely due to different vegetation conditions in the 2012/2013 crop season and to the adjustment to climate [35].…”

An Empirical Algorithm for Estimating Agricultural and Riparian Evapotranspiration Using MODIS Enhanced Vegetation Index and Ground Measurements of ET. I. Description of Method

“…Properly calibrated, Equation 1 can predict crop ET actual . For example, Hunsaker et al [4] found that wheat ET actual predicted from ET o and NDVI was within 5% of values determined in a weighing lysimeter. Gonzalez-Dugo et al [6] compared a VI/crop coefficient remote sensing method for estimating ET actual of corn and soybean crops in central Iowa, US, with three Surface Energy Balance (SEB) methods that utilized thermal bands, and reported root mean square differences of 0.4 mm d −1 for the VI/crop coefficient method and 0.4-0.6 mm d −1 for SEB methods when compared to moisture flux tower measurements.…”

“…Recent studies have combined ground measurements of evapotranspiration (ET), meteorological variables, and vegetation indices (VIs) determined by satellite sensors to project plant water use over diverse biomes, including deserts [1,2], semiarid rangelands [3], agricultural districts [4][5][6], riparian corridors [7,8], rainforests [9], and mixed landscape units at regional [10,11] and global [12,13] scales of measurement. Unlike remote sensing methods based on thermal (NIR) bands on Landsat or other high-resolution satellites, which provide a snap-shot of actual ET (ET actual ) at the time of satellite overpass [14,15], VI methods are useful in projecting ET actual over longer time periods (weeks, months and years), due to the modulated response of VIs to environmental conditions.…”

Irrigation Water Management in Latin America

“…The single K c approach is basically indicated to irrigation planning and design and the dual K c approach is recommended for real time irrigation scheduling. This second approach has been also extensively evaluated (Allen, 2000;Suleiman et al, 2007;Hunsaker et al, 2007).…”