Assessing the climate change impacts on grain sorghum yield and irrigation water use under full and deficit irrigation strategies

Authors: KOTHARI, KRITIKA - Texas A&M University; ALE, SRINIVASULA - Texas A&M Agrilife; BORDOVSKY, JAMES - Texas A&M Agrilife; MUNSTER, CLYDE - Texas A&M University

Submitted to: Journal of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/2019
Publication Date: 8/15/2019
Citation: Kothari, K., Ale, S., Bordovsky, J.P., Munster, C.L. 2019. Assessing the climate change impacts on grain sorghum yield and irrigation water use under full and deficit irrigation strategies. Journal of the ASABE. 63(1):81-94. https://doi.org/10.13031/trans.13465.
DOI: https://doi.org/10.13031/trans.13465

Interpretive Summary: Irrigated agriculture in the semi-arid region of the Texas High Plains faces major challenges from climate change and dwindling groundwater supply from the Ogallala Aquifer. Cropping practices that could mitigate the effects of changing climate and decreasing groundwater availability need to be identified. However, there are a multitude of possible cropping practices to consider, and today’s climate may not be much like that in 2050 and 2100. Working in a project funded by the USDA ARS Ogallala Aquifer Program, scientists from Texas A&M AgriLife and the University of Florida used a crop growth computer model to assess different irrigation strategies for grain sorghum based on crop growth stage or soil water deficit. Forecasted changes in climate change are expected to reduced grain yields under full irrigation by 5% by mid-century (2036 to 2065) and by 15% by late-century (2066 to 2095) as compared to recent yields. The most efficient use of limited irrigation was achieved by applying irrigation during the early reproductive stages of grain sorghum growth (panicle initiation through early grain filling). A 20% deficit irrigation scenario was found to be optimal for current and future conditions. In summary, these results indicated that strategic planning of when and how much to irrigate could help in getting the most out of limited irrigation when growing grain sorghum.

Technical Abstract: Groundwater overdraft from the Ogallala Aquifer for irrigation use and anticipated climate change impacts pose major threats to the sustainability of agriculture in the Texas High Plains (THP) region. In this study, the DSSATCSM-CERES-Sorghum model was used to simulate climate change impacts on grain sorghum production under full and deficit irrigation strategies and suggest optimal deficit irrigation strategies. Two irrigation strategies were designed based on (1) crop growth stage and (2) soil water deficit. For the first strategy, seven deficit irrigation scenarios and one full irrigation scenario were simulated: three scenarios with a single 100 mm irrigation scheduled between panicle initiation and boot (T1), between boot and early grain filling (T2), and between early and late grain filling (T3) growth stages; three 200 mm irrigation treatments with combinations of T1 and T2 (T4), T1 and T3 (T5), and T2 and T3 (T6); one 300 mm irrigation scenario (T7) that was a combination of T1, T2, and T3; and a full irrigation scenario (T8) in which irrigation was applied throughout the growing season to maintain at least 50% of plant-available water in the top 30 cm soil profile. For the second strategy, the irrigation schedule obtained from auto-irrigation (T8) was mimicked to create a full irrigation scenario (I100) and six deficit irrigation scenarios. In the deficit irrigation scenarios, water was applied on the same dates as scenario I100; however, the irrigation amounts of scenario I100 were reduced by 10%, 20%, 30%, 40%, 50%, and 60% to create deficit irrigation scenarios I90, I80, I70, I60, I50, and I40, respectively. Projected climate forcings were drawn from nine global climate models (GCMs) and two representative concentration pathways (RCP 4.5 and RCP 8.5). Climate change analysis indicated that grain sorghum yield under full irrigation was expected to be reduced by 5% by mid-century (2036 to 2065) and by 15% by late-century (2066 to 2095) under RCP 8.5 compared to the baseline period (1976 to 2005). Simulated future irrigation water demand of grain sorghum was reduced due to the shorter growing season and improved dry matter- and yield-transpiration productivity, likely due to CO2 fertilization. Based on the simulated grain sorghum yield and irrigation water use efficiency, the most efficient use of limited irrigation was achieved by applying irrigation during the early reproductive stages of grain sorghum (panicle initiation through early grain filling). A 20% deficit irrigation scenario was found to be optimal for current and future conditions because it was more water use efficient than full irrigation with a minor yield reduction of <11%. In summary, these results indicated that strategic planning of when and how much to irrigate could help in getting the most out of limited irrigation.