Illinois Soil Nitrogen Test and Soil Active Carbon Test Used to Predict Lawn Turf Color.

The Illinois Soil N Test (ISNT) and the Active Soil Carbon Test (ASCT) may predict the responsiveness of turf sites to N fertilization. The ISNT and ASCT are thought to detect the amount of potentially labile N and C in soils, which is correlated to N mineralization and supplying capacity of a soil. If applicable to turf, these tests may be beneficial in guiding N fertilization of turf areas that receive organic amendments. This study was conducted in Connecticut, USA to determine if the ISNT and ASCT could be used to predict color responses of Kentucky bluegrass (Poa pratensis L.) and tall fescue (Festuca arundinacea Schreb.) managed as a lawn. In fall 2007, randomized complete block field experiments were set out and seeded with the two species with varying compost N rates as treatments to produce a wide range of soil N and C concentrations. Compost treatments were repeated and brushed into the same plots in fall 2008 following solid-tine aerification. Soil samples were collected in early May 2009 from each plot and analyzed for concentrations of amino-sugar N and active C. After soil sampling, turf color was measured at approximately two-week intervals from May to October using reflectance meters. Soil amino-sugar N concentrations ranged from 128 to 283 mg/kg, and active C concentrations ranged from 966 to 1221 mg/kg. Significant linear, but weak, relationships were observed for color response of both species to soil amino-sugar and active C concentrations. Maximum turf color response for Kentucky bluegrass and tall fescue has not yet been reached within these ranges of early-season soil amino-sugar N and active C concentrations.