Turfgrass Reflectance Measurements, Chlorophyll, and Soil Nitrate Desorbed from Anion Exchange Membranes

1999) in a variety of locations and soil types. The AEM technique, however, may be more sensitive than tradiThere is not extensive research on the potential of anion exchange tional extractions to treatment differences at low soil membranes (AEMs) for determining available N in soils of turfgrass NO3–N concentrations (Pare et al., 1995; Wander et al., systems, nor on the use of reflectance meters for quantifying turfgrass color. The two objectives of this study were to determine relationships 1995). Studies have reported AEM desorbed NO3–N to between (i) turfgrass color measurements and soil nitrate (NO3–N) be related to N uptake in forage grasses (Ziadi et al., desorbed from AEMs and (ii) reflectance meter measurements and 1999) and in canola (Brassica napus L.) (Qian et al., turfgrass chlorophyll concentration. A field experiment was conducted 1992). In a field experiment with a perennial grassland, on a 90% Kentucky bluegrass (Poa pratensis L.) stand across 2 yr. Collins and Allinson (1999) modeled forage grass yields Anion exchange membranes were inserted into the soil and exchanged to AEM desorbed soil NO3–N using linear response weekly. Desorbed NO3–N from the AEMs was quantified. Turfgrass plateau and quadratic response plateau relationships. color and chlorophyll measurements were taken monthly. Reflectance Critical levels of AEM desorbed NO3–N, above which meter measurements were significantly related to chlorophyll concenthere was no further increase in yield, were typically tration. Linear response plateau models suggested critical levels of between 0.5 and 4 g cm 2 d 1. AEM soil NO3–N, above which turfgrass color did not improve, from 0.31 to 0.43 g cm 2 d 1. These models suggest that critical levels Studies reporting results for the use of AEMs to assess of soil NO3–N could be determined that maximize turfgrass quality available NO3–N in turfgrass systems are limited. Kopp without excessive N application. These findings suggest both AEMs and Guillard (2002) in a field experiment on home lawn and hand-held reflectance meters could be useful tools for N manageturf of mixed species in Connecticut, reported significant ment in turfgrass. quadratic response plateau models of clipping matter dry yields to AEM desorbed soil NO3–N by harvest period. Critical values of soil NO3–N, above which there T is concern about NO3–N losses from managed were no further increases in yield, were typically between turf areas because of negative environmental and 0.4 and 10 g cm 2 d 1. They also reported similar results human heath effects of NO3–N in surface and ground for quadratic response plateau models of visual turf qualwaters. Turf areas are often fertilized according to preity. Critical values typically were between 0.3 and 19 g determined schedules, or fertilization is guided by turf cm 2 d 1. Additionally, Desjardins et al. (1998) reported quality. It would be desirable, however, to manage N ferinitial results for a relationship between tissue-N in turftilization in response to measured soil N. Managing N grass and AEM desorbed soil N. fertilization to optimize turf quality without applying Turfgrass quality is often measured on a subjective excess N may reduce N losses from managed turfgrass visual scale. While visual ratings may be highly reliable areas. Because labile forms of N may be converted into in evaluating treatment differences, they are not compaNO3–N in well-aerated soils, and NO3–N is the form of rable across studies or evaluators. If N management is to N preferred by turfgrasses for assimilation, soil NO3–N be based on quality measurements, objective quality meaconcentrations may serve as a guide for N applications. surements must be employed. Objective quality meaOne method of measuring available soil NO3–N uses surements employed in turfgrass evaluations commonly AEMs. Anion exchange membranes are nearly twoinclude clipping yield and leaf chlorophyll concentradimensional strips of vinyl with anion exchange sites. tion. High clipping yield itself may not be a desirable Because of their two-dimensional nature and small size, characteristic, but may be considered to be an overall they may be used for in situ soil NO3–N measurements measure of plant vitality. Chlorophyll concentration with minimal disturbance to soil and plants. They are similarly may be considered to be a measure of plant relatively easy to handle and process and can be used vitality, or may be viewed as an indirect measure of turf to monitor plant-available NO3–N in soil over time. color (Pocklington et al., 1974). Chlorophyll concentraStudies have shown that AEM desorbed NO3–N is tion and yield measurements, however, suffer from the related to soil NO3–N obtained with traditional soil exdisadvantages of being time and labor intensive. Furthertractions. These studies include correlations to extracmore, direct chlorophyll concentration measurements tion with 0.001M CaCl2 (Qian et al., 1992), 2 M KCl (Pare require access to a spectrophotometer, and are therefore et al., 1995; Subler et al., 1995), and water (Ziadi et al., not practical for all turfgrass managers. Tristimulus chroma meters and chlorophyll reflectance meters are two tools that may be used to assess turfDep. of Plant Science, Unit 4067, University of Connecticut, 1376 grass color quickly and reliably and report quantitative, Storrs Road, Storrs, CT 06269-4067. Received 17 Dec. 2003. *Corresponding author ([email protected]). objective results. Chroma meters measure whole color Published in Crop Sci. 45:259–265 (2005). © Crop Science Society of America Abbreviations: AEM, anion exchange membrane; CIE, Commission Internationale de l’Eclairage. 677 S. Segoe Rd., Madison, WI 53711 USA