1 Modeling Cool-Season Turfgrass Lawn Growth and Quality Responses to Soil Nitrogen and Carbon, and Tissue Nitrogen Concentrations

The goal of turfgrass nitrogen (N) fertilization is to supply sufficient N for aesthetically and functionally high-quality turfgrass without accumulation of excessive soil N, which can facilitate nitrate (NO3) leaching losses. Currently, subjective measures (e.g., assumed N needs of turfgrass species; visual preference of turfgrass quality; historical N rates) remain the primary means used to guide N fertilization of turf. This makes it is more likely that excessive N will be applied to turfgrass. It would be desirable to make N fertilizer application recommendations for turfgrass based on objective testing methods that decrease the chances of excess N fertilization while maintaining acceptable to optimum growth and quality. A three-year field experiment found that Kentucky bluegrass (Poa pratensis L.) and tall fescue (Festuca arundinacea Schreb.) lawn quality and growth were significantly related to soil NO3–N concentrations when modeled with linear-plateau, quadratic-plateau and Cate-Nelson models. The critical soil NO3–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-