Water Stress Detection Under High Frequency Sprinkler Irrigation with Water Deficit Index

A remote sensing package called the agricultural irrigation imaging system ~AgIIS! aboard a linear move irrigation system was developed to simultaneously monitor water status, nitrogen status, and canopy density at one-meter spatial resolution. The present study investigated the relationship between water status detected by AgIIS and soil moisture for the 1999 cotton ~Gossypium hirsutum, Delta Pine 90b! season in Maricopa, Ariz. Water status was quantified by the water deficit index~WDI!, an expansion of the crop water stress index where the influence of soil temperature is accounted for through a linear mixing model of soil and vegetation temperature. The WDI was best correlated to soil moisture through the FAO 56 water stress coefficient Ks model; stability correction of aerodynamic resistance did not improve correlation. The AgIIS did provide field images of the WDI that might aid irrigation scheduling and increase water use efficiency.