Multiplex: a New Diagnostic Tool for Management of Nitrogen Fertilization of Turfgrass.

Multiplex^® is a fluorescence-based optical sensor that measures in real time and in vivo the leaf content of compounds such as chlorophyll and several families of polyphenols (anthocyanins, flavonoïds, hydroxycinnamic acids). We propose here to show that the measurement of leaf chlorophyll and flavonoïd content permits us to evaluate nitrogen status of turfgrass. Actually, experiments have shown that chlorophyll content increases whereas flavonoïd content decreases with increased nitrogen application. So, the chlorophyll-to-flavonoïd ratio named nitrogen balance index (NBI) increases with nitrogen quantity applied on turfgrass. Moreover, NBI measured by Multiplex is well correlated with turfgrass leaf-nitrogen content, better than chlorophyll content alone. Thanks to the NBI, Multiplex measurements permit us to evaluate without any sample preparation quickly and in real time turfgrass nitrogen status. Also, Multiplex gives an objective reference of turfgrass nitrogen level and can help nitrogen fertilization management. The NBI compares easily nitrogen status among greens or sport fields and allows us to adapt supplied nitrogen quantity to each case. By following NBI kinetics of turfgrass, we can see the variation of nitrogen status and particularly when leaf-nitrogen content decreases. This decrease indicates that the fertilizer has been totally used up by turfgrass and that new fertilization is needed. This also avoids over-fertilization that is known to increase turfgrass sensitivity to diseases. Recently, Multiplex has been embedded on a lawnmower to measure NBI during turfgrass mowing and to acquire maps of NBI on greens or sport fields, therefore, nitrogen fertilization was adapted spatially and in time in response to turfgrass needs.