Quantifying water and CO2 fluxes and water use efficiencies across irrigated C3 and C4 crops in a humid climate

Authors: Anapalli, Saseendran; Fisher, Daniel; Reddy, Krishna; KRUTZ, LARRY - Mississippi State University; RAO, SRINIVAS - Oak Ridge Institute For Science And Education (ORISE); Sui, Ruixiu

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/31/2018
Publication Date: 1/2/2019
Citation: Anapalli, S.S., Fisher, D.K., Reddy, K.N., Krutz, L.J., Rao, S.P., Sui, R. 2019. Quantifying water and CO2 fluxes and water use efficiencies across irrigated C3 and C4 crops in a humid climate. Science of the Total Environment. 663:338-350.

Interpretive Summary: The Mississippi Delta relies mostly on groundwater from the Mississippi River Valley Alluvial Aquifer for irrigating crops. This aquifer like all other aquifers in the world that took millions of years to fill are being depleted at alarming rates due to water withdrawals for crop irrigations. Climate variabilities further aggravates for more water inputs in agriculture. Accurate information on water requirements of different crops for absorbing atmospheric carbon dioxide and producing yield is essential for developing environmentally and economically sustainable water management practices. This also help account for carbon dioxide, the most abundant of the greenhouse gases, exchange rates from cropping systems. In this direction, for the first time in the MS Delta, scientists with the USDA ARS Crop Production Systems Research Unit, Stoneville, MS, and Mississippi State University, Mississippi State, MS undertook a study to measure water use efficiencies across corn, soybean and cotton in a predominantly clay soil in the Lower Mississippi (MS) Delta, USA. Carbon dioxide and water flow in and out these three cropping systems were measured. All the three crops took in more carbon dioxide than they respired back into the air. Corn used 19, soybean used 22, and cotton used 14 inches of water in crop production in 2017. These findings can aid in adopting crop mixtures that potentially increase water use efficiency and conserve limited water resources in the region.

Technical Abstract: Underground aquifers that took millions of years to fill are being depleted due to unsustainable water withdrawals for crop irrigation. Concurrently, atmospheric warming due to anthropogenic greenhouse gases is enhancing demands for water inputs in agriculture. Accurate information on crop-ecosystem water use efficiencies [EWUE, amount of CO2 removed from the soil-crop-air system per unit of water used in evapotranspiration (ET)] is essential for developing environmentally and economically sustainable water management practices that also help account for CO2, the most abundant of the greenhouse gases, exchange rates from cropping systems. We quantified EWUE of corn (a C4 crop) and soybean and cotton (C3 crops) in a predominantly clay soil under humid climate in the Lower Mississippi (MS) Delta, USA. Crop-ecosystem level exchanges of CO2 and water from these three cropping systems were measured in 2017 using the eddy covariance method. Ancillary micrometeorological data were also collected. On a seasonal basis, all three crops were net sinks for CO2 in the atmosphere: 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 (negative values show that CO2 is fixed in the plant or removed from the air). The seasonal NEE estimated for cotton was 72% less than corn and 62% less than soybean. Half-hourly averaged maximum net ecosystem exchange (NEE) from these cropping systems were -33.6, -27.2, and -14.2 kg CO2 ha-1, respectively. Average daily NEE were -258, -169, and -65 kg CO2 ha-1, respectively. The EWUE in these three cropping systems were 53, 43, and 24 kg CO2 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.