Effective use of water resources is critical in all areas of the world. There is little understanding of the yearly water use of different agricultural management practices because of the lack of measurement methods. The Bowen ratio system offers the potential to be a robust instrument for year-round use; however, there is concern about the evaluation compared to other standards. Eddy correlation measurements of sensible and latent heat fluxes are considered to be more accurate and robust. These instruments are not feasible to maintain in the field throughout the year. We conducted a study to compare Bowen ratio estimates of sensible and latent heat with eddy correlation measurements. These studies were conducted over several fields in central Iowa at various times of the year from 1992 through 1996. Fields were planted in either corn or soybean with a range of tillage practices. The data set covered 178 individual days of data during this time period. Half-hourly fluxes were compared and showed good agreement, within 10%, with no bias between the methods for the entire record. Bowen ratio measurements using aspirated, electronic humidity sensors can be used to collect accurate data. This type of system can be used to assess the effect of agricultural practices on the regional water and energy balances.