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Sorghum‐Sudangrass Water Productivity Under Subsurface Drip Irrigation

Growing urban areas and industries tend to acquire water from the agricultural sector in order to satisfy their increasing water demand. As a result, agriculture needs to cope with limited available water for irrigation purposes. Yield response to water is, therefore, a basic piece of information that helps farm management to plan for water shortage. This research has determined the effect of water stress on yield production of sorghum‐sudangrass in semiarid eastern Colorado, USA. The research was conducted in an experimental field equipped with subsurface drip irrigation system during the 2015 and 2016 growing seasons. The goal was to define the functional relationship between crop actual evapotranspiration and marketable yield, or the crop water production function; the results support a linear relationship between the two variables, indicating that the productivity of water stays constant with changes in evapotranspiration. Average crop water productivity for sorghum‐sudangrass was 5.49 kg m‐3 for the 2 years of data, which is higher than water productivity of most forage crops. However, sorghum varieties tend to accumulate nitrogen during drought periods and hay nitrogen toxicity becomes a concern under water stress. The crop water production function developed in this research can be used to predict the effect of water stress on yield loss and consequent farm profit loss, which is essential in planning for water transfer and compensating farmers for forgoing irrigation. © 2018 John Wiley & Sons, Ltd.