In December 2003, the US Environmental Protection Agency (USEPA) released a list of 15 additional �candidate pollutants for exposure and hazard screening� with regard to land application of sewage biosolids. Since the USEPA included Ba on this list, we decided to scrutinize soil Ba concentrations from our dryland-wheat (Triticum aestivum L.) summer-fallow agoecosystem experiments that had received 11 biosolids applications (1982-2003) from the Littleton/Englewood, CO (L/E) wastewater-treatment plant at rates from 0 to 26.8 dry Mg ha^-1 . The study was conducted on a Platner loam (Aridic Paleustoll) approximately 30 km east of Brighton, CO. Viewing the soil-extraction data from 1988-2003, we observed significant linear or exponential-rise to a maximum increases in 4M HNO₃ (approximates total concentration) soil extractable Ba in 6 out of 7 years as biosolids rate increased. Concomitantly, we observed significant (P<0.10) linear or exponential declines in surface-soil concentrations ammonium bicarbonate-diethylenetriaminepentaacetic acid (AB-DTPA) extractable Ba as biosolids rate increased in 6 out of 7 years. Generally, biosolids did not affect the 20-60-cm 4 M HNO₃ or AB-DTPA soil concentrations. These results suggest that while total soil Ba is increasing with biosolids application over time, the mineral form of Ba was transformed to a less AB-DTPA-extractable form. Thus, we utilized a sequential metal extraction procedure to identify dominant Ba soil phases, noting the majority of Ba located in the soluble/exchangeable fraction and the more resistant Fe/Mn oxide fraction. Scanning electron microscopy � energy dispersive spectroscopy identified solid BaSO₄ precipitation in our biosolids-amended soils. Our research has shown that biosolids application may increase the total soil Ba; but, may actually decrease the AB-DTPA-extractable (labile) Ba by forming solid phase BaSO₄.