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Title: Grain sorghum production functions under different irrigation capacities

Author
item ARAYA, A - Kansas State University
item KISEKKA, ISAYA - University Of California, Davis
item Gowda, Prasanna
item VARA PRASAD, P.V. - Kansas State University

Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/6/2018
Publication Date: 3/22/2018
Citation: Araya, A., Kisekka, I., Gowda, P.H., Vara Prasad, P. 2018. Grain sorghum production functions under different irrigation capacities. Agricultural Water Management. 203:261-271. doi:10.1016/j.agwat.2018.03.010.

Interpretive Summary: Grain sorghum is one of the main crops grown in western Kansas. Understanding the response of grain sorghum to various irrigation capacities could help to optimize land-water allocation and cropping patterns, reduce the cost of production, improve profitability, increase the water use efficiency while enhance the sustainability of the underlying Ogallala aquifer. In this study, using a crop simulation, we assess the effect of irrigation capacity on grain sorghum when irrigation initiated at planting versus when irrigation initiated at panicle initiation for two widely used grain sorghum cultivars in western Kansas. Irrigation capacity of 3.6 mm/day was found to improve the average yield and enhance water productivity. Similarly, this study showed that relatively high yield was simulated at irrigation capacity of 5-3.6 mm/day when irrigation is initiated at panicle initiation and ended at grain filling and maturity, respectively. In some of the wettest years, even no irrigation was found sufficient. Irrigating grain sorghum from planting to maturity is not recommended unless the growing season is very dry (in such cases, irrigation capacity of 2.5 - 3.6 mm/day may be adequate). This work is based on average yield which did not include economic analysis/profitability, and we recommend further research including net returns and risk analysis.

Technical Abstract: Water is the major factor limiting crop production in semi-arid regions of the southern and central US High Plains. The Ogallala Aquifer is the major source of irrigation water in the region. The water levels in the aquifer have been declining due to water withdrawals for irrigation exceeding mean annual recharge. As a result, some of the wells in the region are not able to meet the crop water requirements due to lower irrigation capacity (IC). Grain sorghum, one of the major cereal crops grown in western Kansas, is considered drought tolerant. There is limited literature on the effect of IC on grain sorghum yield under erratic rainfall patterns of the semi-arid High Plains. Study objectives were to: (1) calibrate and evaluate the Agricultural Production Systems sIMulator (APSIM) model for simulating grain sorghum growth and development; (2) develop grain sorghum water production functions under five ICs, two cultivars, and three irrigation scheduling strategies; and (3) evaluate response of grain sorghum to various IC in western Kansas based on long-term historical climatic conditions. Results showed that the cultivars in APSIM w representative of the experimental cultivars. For early maturing cultivar, Root Mean Square of Error (RMSE), and percent of deviation (d) between the measured and simulated yield were 0.72 t/ha and 3 - 18%, respectively, whereas for late maturing cultivar, the value for corresponding statistical goodness of model fit test was 0.88 t/ha, and 1.7-27%, respectively. The crop water use was also validated with RMSE and d of 15 mm and 1.5 to 6.1%, respectively. Overall the simulated yield and crop water use values strongly agreed with the measured data indicating the satisfactory simulation performance of the model. Highest yield and crop water productivity were obtained from IC of 3.6 to 5.0 mm/day. However, long-term simulation showed that IC of 3.6 mm/day was found to improve average grain sorghum yield and optimize water productivity. In some wet years, lower IC up to 1.7 mm/day or even in some of the wettest years no irrigation was suitable. Our findings indicate that it might not be necessary to irrigate grain sorghum from planting to maturity but if producers are forced to do so by climatic conditions, an IC of 2.5 mm/day was found to produce grain yield similar to that of 5 mm/day. If producers have to irrigate grain sorghum only during the growth period from panicle initiation to maturity, the 3.6 mm/day IC was found to be adequate based on long-term average climate and soils conditions around western Kansas. If producers wish to irrigate only from panicle initiation to grain filling, the highest yield was obtained with IC of 5 mm/day.