Available water effects on water stress indices for irrigated corn grown in sandy soils

Abstract

Water stress indices were investigated in this study to improve irrigation management for com. These indices were used to improve irrigation management by determining irrigation timing and soil water deficit (SWD) on sandy soil using ground-based remote sensing (GBRS) system. The remote sensed data were acquired from the nadir (down-looking) view for canopy reflectance and surface temperature (Ts) measurements as well as an oblique (80°) view. Canopy reflectance measurements were used to calculate vegetation indices to estimate vegetation cover. Experimental data were collected in a com (Zea mays L.) field, Wiggins, Colorado during the 2002 growing season. The study was conducted on two experimental com sites. The first site consisted of six non-replicated plots where the water stress indices were developed. One of the six plots was bare soil and the remaining five plots were drip-irrigated. The second site consisted of half of a center pivot irrigated cornfield where the developed water stress indices were tested. Water stress indices investigated in this study were crop water stress index (CWSI) and water deficit index (WDI). Results of collected experimental data indicated that the WDI was superior to the CWSI since it enables users to determine the amount of irrigation water to be applied to the soil by estimating the SWD at each irrigation besides the irrigation timing that the CWSI is able to determine. Estimating SWD using GBRS data is an innovative technique. SWD provides the necessary information to the irrigator with less fieldwork, and is useful in saving money, time and labor. It can be used with remotely-sensed data measurements, which is a very important feature, especially for large agricultural areas. Results also indicated that the soil-adjusted vegetation index (SAVI) was the best index to represent vegetation cover. If available, oblique (80°) view data should be used to measure Ts to reduce the soil background effect since experimental data of nadir and oblique views were compared to establish baselines of water stress indices.