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Impact of conventional and water-saving irrigation schemes on soybean yield in Big Sunflower River Watershed
Proceedings of the 2020 Mississippi Water Resources Conference

Year: 2020 Authors: Heng T., Feng G., He X., Li F.

Big Sunflower River Watershed (BSRW) is a high-yield agricultural area in the Lower Mississippi river. More than 81% of the total area of the BSRW (approximately 10,488 km2) is agricultural land. Crop yields are often limited by extreme climate events and soil field capacity. Due to these factors, the yield of crops in different regions of BSRW is quite different. For example, in 2013, the soybean yield of Humphreys County, Mississippi was 10.12 bu/acre lower than that of Washington county. Reduction in yield and improving the sustainability of farmland ecosystem is continuous improvement of water use efficiency. However, the model of soybean yield in BSRW has not been calibrated and the effects of different irrigation schemes on soybean yield are rarely reported. In this study, the soil water assessment tool (SWAT model) was calibrated using 20 years (1998-2018) BSRW soybean yield data, then the soybean yield was employed to simulate under non-conventional irrigation schemes. The non-conventional irrigation schemes are the ET-based irrigation method. the amounts of irrigation were set to 50%, 60%, 70%, 80%, 90%, and 100% of crop evapotranspiration (ET). That is, When the soil water storage in 50 cm is lower than the design value of replacement percentage of ET, irrigation was triggered until the irrigation amount reached the ET percentage. The results indicated that soybean yield was positively correlated with ET (R2=0.83). The yield of soybean was 79.23 bu/acre under 80% ET, it was 3.27 bu/acre higher than conventional irrigation. For every 10% increase of ET (50~80%), the average increase of soybean yield is 5.41 bu/acre. Thus this study suggests that the ET irrigation scheduling method can close the gap of soybean yield, so as to make more effective use of irrigation water.

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