Mar 10, 2017

Agronomy & physiology WCRC Agro-Physio-north-america WCRC1
Abstract                                                                         Back to Table of contents

Availability of water causes major variation in cotton yield. Water use efficiency confers meanings of water conservation (i.e., savings of water and/or costs of water application) and transpiration efficiency (i.e., increasing productivity per unit of water transpired).  Because of the commonality in the pathways shared between transpiration and CO2 assimilation, there is a strong link between crop growth and transpiration.  This paper briefly reviews the circumstances leading to water use efficiency of cotton through water conservation, but fully explores our knowledge and water use as it relates to the transpiration efficiency and productivity of the cotton plant.  Emphasis is placed on our understanding of carbon isotope discrimination as it relates to transpiration efficiency and productivity.


Relatively little progress has been made in increasing productivity of cotton or other major crops per unit of water or solar radiation, even though dryland and irrigated yields have increased.  These yield increases have arisen mainly from changes in carbohydrate partitioning favoring fruit production (Gifford et al., 1984), although recent work suggest that genetic advances in yield of Pima cotton varieties (G. barbadense L.) resulted, in part, from selection of plants with higher stomatal conductance and photosynthesis (Cornish et al., 1991).  Nevertheless, selection for photosynthesis and stomatal conductance, per se,  has not been used in improving yield of cotton and other field crops.  Measurements of photosynthesis and stomatal conductance with conventional gas exchange techniques are too variable, measuring plant performance over a brief period time. Integrated over the season small changes in leaf gas exchange can result in large differences in total carbon uptake or water use.  Errors associated with direct gas exchange measurements may be too large to detect small gains in gas exchange efficiency.  In contrast, ∆ appears to be more effective than conventional gas exchange measurements in detecting genotypic differences in transpiration efficiency and productivity for several important crops (Hall et al., 1992).

The crucial role of water in production of cotton will not change.  Industrial, municipal, environmental, and recreational demands for water will intensify. Cotton farmers must continually examine and adopt sound water conservation practices. At the same time scientists must continue to improve our understanding of  crop water use and productivity.  We believe carbon isotope discrimination provides us with a new tool to improve the transpiration efficiency and productivity of field crops. Whether carbon isotope discrimination can be use to improve water use efficiency of cotton remains to be answered.

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