Lawn Turf Color and Density in Relation to Soil Nitrate Concentrations.

The goal of turfgrass N fertilization is to supply sufficient N for acceptable quality without the accumulation of excessive soil N that can result in nitrate-N leaching losses. However, there is no soil-based N test currently used to guide N fertilization of cool-season turfgrasses. This study was conducted in Connecticut, USA to determine if soil nitrate-N could be used to predict color and density responses of Kentucky bluegrass (Poa pratensis L.) and tall fescue (Festuca arundinacea Schreb.) managed as a lawn. In 2007 and 2008, randomized complete block field experiments were set out on the two species with varying N rates as treatments to produce a wide range of soil nitrate-N concentrations. Soil samples were collected at approximately two-week intervals from May through October and analyzed for nitrate-N concentrations. Prior to soil sampling, turf color was measured using reflectance meters. After the last sampling date in October, plugs were removed from each plot and aerial shoots were counted. Significant linear-plateau and quadratic-plateau models for turf color suggested critical levels of soil nitrate-N that maximized color response ranging between 13.4 and 18.4 mg kg^-1 measured with CM1000 meter and between 13.2 and 20.1 mg kg^-1 measured with NDVI meter for Kentucky bluegrass; and ranging between 4.4 and 7.2 mg kg^-1 measured with CM1000 meter and between 4.6 and 8.2 mg kg^-1 measured with NDVI meter for tall fescue when using all data of 2007 and 2008. End-of-season density was maximized when mean soil nitrate-N concentrations were around 7.0 mg kg^-1 for Kentucky bluegrass and around 5.0 mg kg^-1 for tall fescue, respectively. These results suggest that frequent sampling for soil nitrate-N could be used to guide N fertilization recommendations of lawn turfgrasses, provided that water inputs were not excessive during the sampling period.