The objective of this study was to examine to test the relationship between net ecosystem fluxes and absorbed photosynthetically active radiation (PAR) as a method of estimating production at regional scales from field-scale data. The Soil Moisture Experiment 2005 was conducted in Walnut Creek Watershed near Ames IA during which eddy-correlation towers were used to measure daily net fluxes of carbon dioxide in various fields of corn, soybean and alfalfa. Meteorological data were used to estimate daily incident PAR. Imagery from Landsat 5 Thematic Mapper (TM), Indian Resource Satellite Advanced Wide Field Sensor (AWiFS), and NASA Terra Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) were combined to produce remotely sensed estimates of the fraction of absorbed PAR over the growing season for each field. The slope between the net flux of carbon dioxide and absorbed PAR was the estimated light use efficiency. Comparison to NASA Terra Moderate Resolution Imaging Spectroradiometer (MODIS) standard data products show that the differences in net carbon flux over the Iowa region have significant differences, which could be important for the monitoring the North American Carbon Budget. The differences in light use efficiency between corn (C4 photosynthesis) and soybean and alfalfa (both C3 photosynthesis) indicate that crop type is an important land-cover input for regional estimation of primary production from MODIS.