Pigeonpea [<i>Cajanus cajan</i> (L.) Millsp.] is an important legume crop widely cultivated in tropical and subtropical climates of the world. Interest in this crop is growing in many countries because of its multiple uses as a source of food, feed, fuel, and fertilizer. However, the performance of pigeonpea in Southeastern US has not been well investigated. We conducted an experiment in Nashville, Tennessee to test the effects of two planting dates, three densities, and four varieties on pigeonpea ecophysiology that included leaf photosynthesis, stomatal conductance, transpiration, water use efficiency (WUE), leaf area index (LAI) and soil respiration. Results indicated that the plants in the late planting plots had higher photosynthetic rate, stomatal conductance and transpiration. There were significant differences in the levels of leaf photosynthesis, stomatal conductance, transpiration, WUE and LAI among all four varieties. W3 and G1 showed higher photosynthetic rate and LAI than W1, and W3 had higher WUE than G2 and W1. Planting densities had no significant effect on all variables studied. This study indicated that late planting of variety G1 or W3 resulted in higher WUE and yield, but did no significant influence soil CO₂ emission

Many factors such as climate and agricultural practices influence the ecophysiology of legume crops. As an important legume crop, pigeonpea (Cajanus cajan) has been grown mainly in arid, semi-arid tropical and subtropical regions of the World. However, performance of pigeonpea in southeastern United States has not been extensively investigated. To test the effects of climate and agricultural practices on the ecophysiology of pigeonpea, we conducted a two-year field experiment in Nashville, Tennessee. Precipitation during the growing season showed contrasting patterns with fall drought in 2010 and frequent precipitation in 2011. Four pigeonpea varieties at three planting densities were evaluated in both years. Measurements included maximum net leaf photosynthesis, stomatal conductance, transpiration, water use efficiency (WUE), leaf area index (LAI), and soil respiration. We found strong interannual variations in all variables investigated. Leaf photosynthetic rates, stomatal conductance, transpiration and LAI were significantly higher in 2011 than in 2010. The high values observed in 2011 were mainly due to high precipitation rates during and after the flowering time. Pigeonpea varieties G1 and W3 had higher photosynthetic rates and LAI while variety W3 had the highest WUE. Planting density did not influence these ecophysiological variables except for plant transpiration. Our results indicated that variety selection could improve pigeonpea performance under varying climatic conditions. Although pigeonpea varieties are adaptable to drought, irrigation and growing in moist climatic regions could significantly enhance its ecophysiological performance and yield.