Proceedings of the 2019 Mississippi Water Resources Conference

Year: 2019 Authors: Anapalli S.S., Reddy K.N., Krutz J.

Aquifers all around the world, that took millions of years to fill are being depleted due to unsustainable water withdrawals for crop irrigation. The Mississippi (MS) Delta, one of the most important agricultural production regions in the USA, relies mostly on water from the MS River Valley Alluvial Aquifer for irrigation needs. Soybean represents about 53% of the irrigated area, while the remaining shared between other crops and aquaculture. Pumping water from this shallow aquifer beyond its natural recharge levels has already resulted in significant aquifer declines, threatening the future of irrigated agriculture in the MS Delta. Accurate information on crop evapotranspiration demands (consumptive water requirements; ET) of staple crops in the MS Delta is essential for developing environmentally and economically sustainable water management practices. We quantified ET of corn (a C4 crop) and soybean and cotton (C3 crops) in a predominantly clay soil under humid climate in the Lower MS Delta using the eddy covariance method. In 2017 season, corn, soybean, and cotton fixed 31331, 23563, and 8856 kg ha^-1 of CO2 in exchange for 483, 552, and 367 mm of ET, respectively. Crop durations were 120, 135, and 137 days, respectively for corn, soybean, and cotton. Maximum LAI and average grain yield produced were 5.5 and 12772 kg ha^-1, 5.5 and 4777 kg ha^-1, and 3.0 and 1260 kg lint ha^-1, respectively, for these crops. The seasonal net ecosystem exchange (NEE) of CO2 estimated for cotton was 72% less than corn and 62% less than soybean. Estimated average daily ET of corn was 4.0 mm, soybean was 3.9 mm, and cotton was 3.0 mm. The ecosystem water use efficiency in these three cropping systems were 53, 43, and 24 kg CO2 ha^-1 mm^-1 of water. The WUE in grain production of corn was 26 kg ha^-1 mm^-1 and soybean was 9 kg ha^-1 mm^-1 of water. Results of this investigation can help in adopting crop mixtures that are environmentally and economically sustainable, conserving limited water resources in the region.