Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/3/2008
Publication Date: 5/1/2009
Citation: Tolk, J.A., Howell, T.A. 2009. Transpiration and yield relationships of grain sorghum grown in a field environment. Agronomy Journal. 101(3):657-662. Interpretive Summary: Crop growth is directly related to transpiration. Transpiration is the water that passes through and out of the crop to support the cellular processes that make it grow. The final weight of the crop, or its biomass, is a measure of how efficient the crop was in using water as transpiration for its growth. Researchers have been studying this relationship since the early 19th century, because it is also related to the production of grain needed for food. An important goal for scientists through the years has been to develop new varieties of crops with improved production. This has occurred in crops such as wheat. Our objective was to grow grain sorghum in a field environment to measure transpiration and biomass to compare the results with the early studies. We found that the grain sorghum in this study did not use the water any more efficiently for biomass production than the grain sorghum grown in the early 19th century. The potential to improve grain sorghum production may still exist.
Technical Abstract: The ability of plants to convert transpiration into dry matter has been studied since the early 20th century. Research has compared differences among species using transpiration efficiency (TE), the ratio of biomass yield (Yb) to transpiration (T); and m and k, which are the slopes of the linear Yb/T relationship normalized by atmospheric evaporative demand. The objective of this research was to develop transpiration and biomass relationships (TE, m, and k) and the transpiration and grain relationship (TEg) of grain sorghum (Sorghum bicolor L. Moench) grown in a field environment. Grain sorghum was grown in 1998 and 1999 in weighable lysimeters using stored soil water only and in a rain shelter facility. This approach limited the irrigation and precipitation evaporation components of E so that T estimated (Test) using lysimetry in a field environment was emphasized. The TE remained constant through a range of water availability. The TE was similar between the two years, and the combined data produced a slope of the Yb/Test relationship of 3.5 g m**-2 mm**-1. This was similar to the 3.3 g m**-2 mm**-1 reported for sorghum in the early 20th century, but smaller than current field studies which ranged from 4.0 g m**-2 mm**-1 to 5.7 g m**-2 mm**-1. The TEg was 2.6 g m**-2 mm**-1. Normalization of Test by seasonal averages of reference evapotranspiration and vapor pressure deficit produced significant differences between years in the slopes of the relationships. Transpiration efficiency did not require normalization for variations in climate between years.