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, 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 to November and analyzed for nitrate-N concentrations. Prior to soil sampling, turf color was measured using reflectance meters. After the last sampling date in November, plugs were removed from each plot and aerial shoots were counted. Significant linear-plateau models for turf color suggested critical levels of soil nitrate-N ranging between 9.8 and 17.4 mg kg^-1 for Kentucky bluegrass, and between 4.3 and 7.7 mg kg^-1 for tall fescue, respectively. End-of-season density was maximized when seasonal mean soil nitrate-N concentrations were 16.6 and 8.5 mg kg^-1 for Kentucky bluegrass and tall fescue, respectively. These results suggest that N fertilization of lawn turf could be guided by a frequent soil nitrate-N test.