Nitrogen management of turfgrass utilizing reflectance meters, anion exchange membranes, and timing of fall fertilization

As areas of managed turfgrass expand throughout Connecticut and elsewhere in the nation, there is concern about the negative impacts of nitrate leaching losses from turfgrass on surface and groundwater quality. The goal of nitrogen management for turfgrass is to apply sufficient nitrogen for high quality turf while limiting excess application, which can facilitate nitrate leaching. Because no soil test for nitrogen is commonly used for turfgrass in humid climates, it would be desirable to make nitrogen fertilizer application recommendations based on measured soil nitrogen or measured turfgrass color. It is also desirable to adjust recommendations for the timing of fall fertilizer applications to account for the climate of southern New England. A two-year field experiment found measurements from reflectance meter measurements on turfgrass to be significantly related to turf tissue chlorophyll concentration. This result suggests that reflectance meters might be useful tools in determining nitrogen status of turf. Another two-year field experiment in Connecticut found that nitrate mass in percolate water from turfgrass increased with later dates of application of fall fertilizer, but that there was no additional improvement to turf color in the following spring from fertilizing beyond 15 October. This result suggests that current recommendations for Southern New England for the application of nitrogen fertilizer in November are not compatible with water quality goals. Two field experiments and one greenhouse experiment were performed to determine if soil nitrate desorbed from anion exchange membranes (AEMs) could determine turfgrass color, clipping yield, and nitrate leaching from turfgrass. Turfgrass color and yield were related to AEM soil nitrate with linear-plateau and Cate-Nelson models. These models suggested critical values of soil nitrate above which turf had a low probability of additional quality response. Flow-weighted nitrate concentration and cumulative nitrate mass loss was exponentially related to mean AEM soil nitrate. These results suggest that nitrogen fertility of turf should be managed in response to measured soil nitrate, and that AEMs might be a tool to predict a range of soil nitrate values sufficient for high quality turf without producing high nitrate leaching losses.