Dwarfing of tall sorghums (Sorghum bicolor, L.) provides lodging resistance and adapts the crop to mechanical harvesting. The effect of height on water use and yield are not well known. To help explain the effect of height on water use efficiency (WUE), we compared total water use, photosynthetic light interception, and dry matter accumulation of three height isolines of sorghum in three stands — pure, mixed and alternating rows. Other measurements included leaf temperature, stomatal resistance, and xylem-water potential. Tall plants, which had the highest evapotranspiration in both seasons, also had the highest WUE for dry matter; but the dwarf plants were more efficient with respect to grain water use. Total dry matter yields were in direct relation to the isoline heights. Dwarf plants consistently had the warmest canopy temperature of the isolines during peak insolation periods. Regression of dry matter production on normalized transpiration gave a slope factor (k) of 0.173, 0.222 and 0.296 mb for the double-dwarf, dwarf, and tall isolines, respectively. Photosynthetically active radiation (PAR) interception in the double-dwarf canopy was lower than in other plots. Fewer tillers and loose leaf arrangement on the tall plants allowed higher PAR transmission and, therefore, lower PAR interception compared with the dwarf canopy, though the differences were not statistically significant. Differences in dry matter accumulation among plots were mainly in the stem fraction; tall plants produced about the same quantity as the mixed and alternated plots. The dwarf, with its lower dry matter, produced the most grain in both seasons. Tall plants yielded more grain in the mixed, than in pure or alternated canopies. The short, double-dwarf plants in mixed plots were shaded and, therefore, yielded considerably less dry matter and grain.
Rising ozone concentrations decrease soybean evapotranspiration and water use efficiency whilst increasing canopy temperature
