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Agroclimatology

Evaluation of Two Temperature Stress Indices to Estimate Grain Sorghum Yield and Evapotranspiration

^a Dep. of Ecol. and Nat. Resour. Manage., Cent. for Dev. Res. (ZEF), Univ. of Bonn, Walter Flex Staße 3, 53113 Bonn, Germany
^b Dep. of Agric. Eng., Federal Univ. of Technol., P.M.B. 704, Akure, Nigeria

^* Corresponding author (ayodele_ajayi{at}yahoo.com)

Received for publication March 20, 2003. This study was performed to examine the relationship between canopy temperature (T_c)–based stress indices and grain yield and evapotranspiration (ET) of sorghum [Sorghum bicolor (L.) Moench]. The crop was subjected to 14 differentially irrigated treatments of which two were controls maintained at well-watered and dry conditions during three consecutive years. Soil water content and T_c were measured, and relationships between T_c–based stress indices [stress degree day (SDD), temperature stress day (TSD), and crop water stressed index (CWSI)] and yield as well as ET were examined. The T_c–air temperature (T_a) difference varied from –2 to +8°C in the stressed treatments and maintained a negative value for most of the time in the well-watered treatment. The relationship between T_c – T_a and vapor pressure deficit, commonly referred to as baseline in the determination of CWSI, was examined on function of wind speed and global solar radiation. Although observations showed that T_c can be influenced by climatic condition, this study confirmed that it can serve as a useful indicator of water stress in the case of sorghum. High correlation found between T_c–based stress indices TSD, SDD, and CWSI and ET as well as grain yield suggest the possibility of using these relationships for predictive purposes.

Abbreviations: CWSI, crop water stressed index • DAS, days after sowing • ET, evapotranspiration • SDD, stress degree day • T_a, air temperature • T_c, canopy temperature • TSD, temperature stress day