Canopy temperature and water stress of cotton crops with complete and partial ground cover

Abstract

The use of canopy and air temperature differences to compute a crop water stress index (CWSI) for assessing plant water status was investigated using cotton crop canopies that either fully or partially covered the ground. The complete ground cover canopy condition was studied in a well watered moisture regime in a rainout shelter with measurements made on six Texas cotton race stocks. The partial ground cover canopy situation was investigated in a well watered moisture regime of a commercial cotton variety ‘Paymaster 266’ grown in the field. The slope of the nonstressed baseline of the CWSI for a cotton canopy with about 50% ground cover was approximately one-half that reported for full canopies. Values of CWSI calculated with “theoretical” and “empirical” procedures agreed more closely under a complete canopy condition than under a partial canopy situation. Values of aerodynamic resistance (r a ) and canopy resistance for well watered soil moisture conditions (r ep )were estimated in order to use the theoretical procedure of computing CWSI. Values of r a ranged from 10 to 15 sm−1 and r cp from 50 to 60 sm−1. Both the theoretical and empirical procedures showed much promise, but more information is needed to develop techniques for evaluating r a and r cp under differing canopy and environmental conditions.