Sand is commonly used as the principal component of rootzone mix in golf course putting greens, but it does not provide sufficient nitrogen (N) for adequate turf performance. The United States Golf Association recommends peat as an amendment for the sand layer, but this material seems to be poor in helping the recolonization of microbial populations needed for N transformation in rootzones. Although little information is available about soil microbial ecology in land application of biosolids - an aged stabilized nutrient source from municipal wastewater treatment, recent results from our long-term experiment at Fulton County, Illinois indicate that biosolids promote soil microbial populations, even where soils received previous applications of biosolids with higher metal concentrations. We hypothesize that biosolids amendment can increase the populations of beneficial microorganisms in putting green rootzones. In this study, we examine effects of biosolids amendments on soil microbial ecology parameters to evaluate their effectiveness in maintaining fertility of golf course putting green rootzones.
Plots of 20 treatments applied as various materials on a volume percentage basis as rootzone amendment were established in a putting green at the North Shore Country Club golf course, Glenview, Illinois, USA in 1997. Four treatments: sand (control), sand with Dakota reed sedge peat (10%), sand with yard-waste compost (10%), and sand with biosolids (10%) were selected for the study. The yard-waste compost was included in the study because it is currently being considered as alternative to peat for rootzone amendment in golf courses. Each amendment was blended with feltes sand to construct a rootzone of 30 cm depth placed on top of pea gravel. Each plot was separated by an 800 mil high density polyethylene sheet. Due to high construction and operational costs of putting greens, the treatments were not replicated. All plots were sown with creeping bentgrass (Agrostis palustris), which was later mowed close to the soil surface as commonly done for putting greens. The nitrogen fertilizer was applied at a much lower (106 kg N ha-1 in 2004) than the recommended rate. The entire rootzone soil (0-30 cm) was sampled using an auger in July (summer) 2003, and quarterly, starting from April 2004 (spring) with subsequent sampling in July (summer) and September (fall) 2004, and April (spring) and July (summer) 2005. Three composite soil samples, consisting of 6 sampling points, were collected in each treatment. The samples were analyzed for chemical and microbial parameters.
The data showed that at six years after the establishment of the putting green, soil organic carbon was higher in peat (3.3 g kg-1) and compost (3.5 g kg-1) rootzone than in the control (sand only) (0.73 g kg-1), but lower than in the biosolids rootzone (6.6 g kg-1). Potentially mineralizable N - PMN (2.5 – 4.2 mg kg-1) and microbial biomass C - MBc (14.0 - 35.2 mg kg-1) did not differ among control, and peat and compost rootzones. The biosolids-amended rootzone had higher PMN (11.7 mg kg-1) and MBc (72.8 mg kg-1) than all other rootzones. The populations of nitrifiers (ammonium oxidizers and nitrite oxidizers) and concentrations of nitrate in most seasons from summer 2003 to summer 2005 were higher in amended rootzones than in the control. Rootzone ammonium oxidizer populations were higher in biosolids (5,300 g-1 soil – summer 2003 and 13,100 g-1 soil – fall 2004) than in the peat (1,200 g-1 soil - summer 2003 and 6,900 g-1 soil - fall 2004), and compost (600 g-1 soil - summer 2003) amendments. The nitrite oxidizer populations were higher in amendments of biosolids (5,300 and 49,800 g-1 soil) and compost (8,100 and 64,800 g-1 soil) than in peat (3,100 and 7,300 g-1 soil) in both spring and fall 2004, and in biosolids (23,900 g-1 soil) than in compost (8,300 g-1 soil) and peat (4,700 g-1 soil) in summer 2005. In nearly all seasons, the nitrate concentrations in rootzone amended with either biosolids (3.16 – 19.3 mg kg-1) or compost (2.79 – 17.7 mg kg-1) are higher than that with peat (1.83 – 14.4 mg kg-1) and control (0.81 - 15.2 mg kg-1). In summer 2003, the nitrate concentration was even higher in the biosolids-amended (12.6 mg kg-1) than compost-amended (7.3 mg kg-1) rootzone. The results from the study indicate that biosolids could maintain higher soil microbial populations and N fertility, and thus are potentially a better amendment than peat for rootzones of golf course putting greens.