Predicting Cool-Season Turfgrass Response with Solvita Soil Tests, Part 2: CO 2 –Burst Carbon Concentrations

Current turfgrass fertilizer recommendations do not account for plant-available soil N mineralized from labile C fractions. The Solvita Soil CO₂–Burst (SSCB) test can measure mineralizable C via soil CO₂ respiration. This study was conducted across 3 yr (2014–2016) in Connecticut to determine: (i) if SSCB–C concentrations are correlated to responses from predominately Kentucky bluegrass (Poa pratensis L.) and tall fescue [Schedonorus arundinaceus (Schreb.) Dumort.] lawns, and (ii) the probability of turfgrass responses being equal to or greater than responses from common urea rates in relation to SSCB–C concentrations. Randomized complete block design field experiments were set out with 23 rates of 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 SSCB–C concentrations and correlated with turfgrass responses. Growth and quality responded positively and linearly (P < 0.001) to SSCB–C concentrations, but variability was high and correlations were relatively weak. When spring soil SSCB–C concentrations were ≥91, 113, 166, and 211 mg kg⁻¹, there was a ≥90% probability that overall combined responses across species and variables would be equal to or greater than responses obtained from urea rates of 50, 100, 150, and 200 kg N ha⁻¹ yr⁻¹, respectively. The SSCB test has promise for predicting the probability of soils supporting turfgrass whose performance equals or exceeds benchmark values. This would be helpful in guiding N fertilization, but high variability within the test may limit its predictive ability.