Submitted to: Irrigation Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/30/2006
Publication Date: 8/1/2007
Citation: Bajwa, S.G., Vories, E.D. 2007. Spatial analysis of cotton (Gossypium Hirsutum L.) canopy responses to irrigation in a moderately wet area. Irrigation Science. 25(4):429-441.
Interpretive Summary: Accurate irrigation scheduling is important to ensure maximum yield and optimal water use in irrigated cotton; however, irrigation research in the past has shown mixed results. This study hypothesizes that better understanding the plant response to water stress could be valuable in improving irrigation scheduling. High levels of water stress did not develop during the study period, resulting in no significant differences in lint yield associated with the irrigation treatments. However, the study showed that both canopy temperature and reflectance had the potential to indicate water stress and were highly correlated to soil moisture. These findings can lead to improved irrigation scheduling recommendations for cotton, resulting in more efficient use of irrigation water.
Technical Abstract: Accurate irrigation scheduling is important to ensure maximum yield and optimal water use in irrigated cotton. However, irrigation scheduling research in the past has shown mixed yield responses to irrigation, which could be attributed to inaccuracies in the irrigation scheduling programs. This study hypothesizes that plant response to water stress, if monitored closely, could be a valuable parameter in irrigation scheduling. Field experiments were conducted in the 2003-2004 crop seasons with three different irrigation levels to study cotton response to water stress. The responses of canopy reflectance and temperature to water stress were analyzed. Although canopy temperature is a good indicator of water stress, it is directly related to vapor pressure deficits (VPD). Therefore, we also studied the effect of VPD on canopy temperature. Rainfall was plentiful in both seasons and high levels of water stress did not develop, resulting in no significant differences in lint yield associated with the irrigation treatments. Even in relatively wet years, both canopy temperature and reflectance showed great potential to indicate water stress. The reflectance-based vegetative indices, NDVI and GNDVI and canopy-temperature-based indices, ST and CWSI showed significant differences among irrigation treatments. These four indices were also highly correlated to soil moisture tension at 0.2 m depth. The results also verified that very large VPD (> 2.5 kPa) and extremely low VPD (< 1 kPa) masked the canopy temperature difference with respect to ambient temperature.