Predicting Cool-Season Turfgrass Response with Solvita Soil Tests, Part 1: Labile Amino-Nitrogen Concentrations

Current turfgrass fertilizer recommendations do not account for potential mineralizable N in the soil. The Solvita Soil Labile Amino-Nitrogen (SLAN) test measures a labile fraction of soil N. This study was conducted across 9 yr (2008-2016) in Connecticut to determine if responses from predominately Kentucky bluegrass (Poa pratensis L.) and tall fescue [Schedonorus arundinaceus (Schreb.) Dumort.] lawns are correlated to SLAN-N concentrations, and to determine the probability of turfgrass responses equaling or exceeding the response from benchmark urea rates in relation to SLAN-N concentrations. Randomized complete block design field experiments were set out with 23 rates of an organic fertilizer (0-2000 kg N ha(-1) yr(-1)) and four different rates of urea (50, 100, 150, and 200 kg N ha(-1) yr(-1)). Yearly spring soil samples were analyzed for SLAN-N concentrations, and turfgrass growth and quality responses were collected during the growing seasons. Turfgrass responded positively and linearly (P < 0.001) to SLAN-N concentrations, but correlations were relatively weak to moderate. When spring soil SLAN-N concentrations were >= 158, 165, 198, and 217 mg kg(-1), there was a >= 90% probability that overall combined responses across species and measured variables would be equal to or greater than responses obtained from 50, 100, 150, and 200 kg urea N ha(-1) yr(-1), respectively. The SLAN test has promise as an objective soil test to categorize the N fertilization response potential of turfgrass soils, and this would be helpful in guiding N fertilization.