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Abstract: In an effort to generate more information on the use of biosolids in the turf industry, a study was conducted to compare the effectiveness of biosolids with recommended organic sources in enhancing soil microbial populations and N availability in putting green sand rootzones. The treatments included four types of rootzones as follows: sand (control), sand mixed with Dakota reed-sedge peat (10%, v/v), sand mixed with yard-waste compost (10%, v/v), and sand mixed with biosolids (10%, v/v), which were established at the North Shore Country Club golf course, Glenview, IL, USA in 1997. All plots received the same fertilizers mainly in organic forms at 100kgNha−1 year−1. Creeping bentgrass (Agrostis palustris) turf was established, and was managed as a practice putting green. Soil microbial biomass in the rootzone (0–30cm) was higher either under compost (fall 2004 and summer 2005) or biosolids (summer 2003) than other treatments. Rootzone ammonium oxidizer populations were higher with biosolids (5400g−1 soil) than peat (1200g−1 soil) and compost (500g−1 soil) amendment and in control (400g−1 soil) in summer 2003. The nitrite oxidizer populations were higher with biosolids (24000g−1 soil) than compost (8300g−1 soil) and peat (4700g−1 soil) amendment and in control (3700g−1 soil) in summer 2005. Soil potentially mineralizable N, also being lowest in control, was higher in the biosolids-amended than compost- and peat-amended rootzones. In most seasons, the nitrate concentrations in biosolids rootzone (3.16–19.3mgkg−1) were higher than in compost (2.79–17.7mgkg−1), peat (1.83–14.4mgkg−1), and control rootzone (0.81–15.2mgkg−1). The study indicates that while compost could restore soil microbial biomass better than peat, biosolids could maintain greater N supply than peat and compost. [Copyright &y& Elsevier]