Date of Completion

12-12-2013

Embargo Period

12-12-2013

Keywords

Turfgrass, Turfgrass management, Nutrient management, Soil nitrogen, Soil carbon, Soil analysis, Plant analysis, Nitrogen, N fertilization, Mineralization

Major Advisor

Karl Guillard

Associate Advisor

Thomas F. Morris

Associate Advisor

Jason Henderson

Field of Study

Plant Science

Degree

Doctor of Philosophy

Open Access

Open Access

Abstract

ABSTRACT

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-1 for Kentucky bluegrass, and from 2.5 and 10.1 mg kg-1 for tall fescue. A five-year field experiment found that Kentucky bluegrass and tall fescue lawn color quality and growth were highly related to soil N measured by the Illinois Soil N Test (ISNT-N) and labile soil carbon measured by a permanganate-oxidizable carbon (POXC) test. There was a low probability of meaningful Kentucky bluegrass and tall fescues lawn responses to N fertilization when spring ISNT-N and POXC concentrations exceed 250 mg kg-1 and 1300 mg kg-1, respectively. Tissue N analysis was performed on the turfgrass clippings collected from the 3- and 5-year field experiments, and the relationship between leaf total N concentration and turf color quality and growth response was identified and modeled using the Macy approach. These models indicated critical concentration of leaf N above which there is luxury consumption and below which there is poverty adjustment until a minimum concentration is reached. Averaged across all variables and seasons (spring, summer, and fall), the sufficiency ranges of N concentration in the clippings were estimated to be 32 to 46 g kg-1 for Kentucky bluegrass, and 28 to 42 g kg-1 for tall fescue. Results from all studies suggest that frequently-measured soil NO3-N, ISNT-N, POXC, and clippings total N concentrations show promise as objective guides for nitrogen fertilization of cool-season turfgrass lawns. Adoption and implementation of these tests to turfgrass systems should help to decrease excess N loading rates, resulting in reduced maintenance costs and lower chances of water quality impairment.

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