Analysis of Drought Tolerance and Water Use Efficiency in Cotton, Castor, and Sorghum

Water management and water use efficiency have become real issues amid agriculture production throughout the country.  In water limiting conditions, it is imperative to better understand crop water use efficiency.  The objective of this study is to determine physiological, agronomic and economic water use efficiency (WUE) for three crops (sorghum, cotton and castor) and to maximize profitability for a given cropping system and irrigation capacity.  Studies were initiated at TTU farms in New Deal and Lubbock.  Thirteen subsurface drip irrigation (SDI) zones (~0.25 ac each) were utilized for each study.  Irrigation treatments ranged from 0 to 0.24” maximum per day.  Measurements consists of yield, soil volumetric water content, canopy intercepted radiation, crop growth rate, photosynthesis, stomatal conductance, leaf water potential, WUE, radiation use efficiency (RUE), net returns.  ). Photosynthetic rates are similar in cotton and sorghum but lower in castor.  Transpiration is lowest in sorghum at similar photosynthetic rates indicating a better use of water when compared to the other crops.  However, for each unit decrease in conductance, the resulting decrease in photosynthesis is less for cotton and castor than sorghum.  Higher irrigation rates could possibly be wasted due to no unit of increase in photosynthesis at a given conductance level.