Gross primary production and ecosystem respiration in irrigated and rainfed maize-based agro-ecosystems

Year-round measurements of CO2 exchange were made in irrigated and rainfed maize-soybean fields during eight years in eastern Nebraska. Gross primary production (GPP) and ecosystem respiration (Re) were calculated from our CO2 flux data. Annual GPP in irrigated maize ranged from 1700 to 1900 g C m-2 y-1 and slightly lower (1480 to 1640 g C m-2 y-1) in rainfed maize. Irrigated soybean GPP varied from 900 to 1071 g C m-2 y-1 and rainfed values ranged from 890 to 906 g C m-2 y-1. Annual magnitudes of maize Re ranged from 1200 to 1300 and 1000 to 1130 g C m-2 y-1 in irrigated and rainfed conditions, respectively. Soybean Re magnitudes varied from 950 to 1120 and 830 to 930 g C m-2 y-1 under irrigated and rainfed conditions, respectively. We will examine the role of factors controlling GPP at daily and seasonal scales. Factors controlling Re at daily and seasonal scales will also be investigated. Non-growing season Re will also be quantified and studied in terms of key controlling variables.