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Title:   Author  item
                                            Baker, Jeffreyitem
                                            Gitz, Dennisitem
                                            Payton, Paxtonitem
                                            Mahan, Jamesitem
                                            Lascano, Robert
  Submitted to: ASA-CSSA-SSSA Annual Meeting Abstracts
                                    Publication Type: Abstract Only
                                    Publication Acceptance Date: 11/2/2014
                                    Publication  Date: 11/6/2014
                                    Citation: Baker, J.T., Gitz, D.C., Payton, P.R., Mahan, J.R., Lascano, R.J. 2014. Deficit irrigation: Arriving at the crop water stress index via gas exchange measurements[abstract]. American Society of Agronomy, Crop Science Society of America, Soil Science Society of America Annual Meeting. November 2-6, 2014. Long Beach, California.Interpretive Summary:
                                Technical Abstract: Plant gas exchange provides a highly sensitive measure of the degree of drought stress. Canopy temperature (Tc) provides a much easier to acquire indication of crop water deficit that has been used in irrigation scheduling systems, but interpretation of this measurement has proven difficult. Our goal was to test the ability of Tc to quantify the degree of crop water deficit by comparing Tc with simultaneous measurements of cotton leaf-level gas exchange parameters in the field over two growing seasons.  Comparisons between Tc and leaf-level gas exchange were accomplished by measuring Tc diurnally with hand-held infrared thermometers and controlling cuvette leaf temperature (TL) equal to Tc and then measuring light saturated leaf level net assimilation (A) and stomatal conductance (g).  As plant water deficit became more severe, leaf level gas exchange tended to decline with rising TL. However, we found that A and g could vary by more than twofold at a given TL, indicating that Tc was not a particularly robust indicator of the degree of drought stress. Using regression analysis (MAXR, SAS Institute) we found that variables used by the Crop Water Stress Index (CWSI) were better predictors of the degree of drought stress than TL alone. We conclude that canopy minus air temperature differential (Tc -Ta) either alone or in combination with vapor pressure deficit (VPD) should provide a better predictor of the degree of drought stress than Tc alone.


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