Relating Turfgrass Growth and Quality to Frequently Measured Soil Nitrate

Currently, there is no soil‐based N test used to guide N fertilizer recommendations for turfgrass. This study was conducted across 3 yr in Connecticut to determine if frequent measurement of soil nitrate–N (NO 3 –N) could be used to estimate color, density, clippings yield, clippings total N concentration, and clippings N uptake in Kentucky bluegrass ( Poa pratensis L.) and tall fescue ( Festuca arundinacea Schreb.) lawns. Randomized complete block field experiments were set out on the two species with nine N rates. Soil cores and clippings were collected at 2‐wk intervals from May through October and analyzed for concentrations of NO 3 –N and total N, respectively. Turfgrass color was measured with chlorophyll and normalized difference vegetative index meters, and shoot count density was measured after the last sampling. Significant ( p < 0.001) Cate‐Nelson, linear‐plateau, and quadratic‐plateau models were observed for all relative measures of turfgrass growth and quality as a function of soil NO 3 –N concentrations. The critical soil NO 3 –N concentrations for the three models that indicated the beginning of a plateau response or marked the Cate‐Nelson change point between likely or unlikely response ranged from 3.7 and 18.0 mg kg −1 for Kentucky bluegrass and from 2.5 and 10.1 mg kg −1 for tall fescue. Probability plots indicated a high likelihood of acceptable turfgrass responses at the lower range of the critical concentrations suggested by the Cate‐Nelson model. These results suggest that frequent measurement of soil NO 3 –N may help to guide N fertilization of Kentucky bluegrass and tall fescue when managed as lawns.