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.