Using a chlorophyll meter to determine the chlorophyll concentration,nitrogen concentration, and visual quality of St. Augustinegrass

Abstract

Because high rates of nitrogen fertility are necessary for producing high-quality turfgrasses, quick, reliable methods of determining the N status of turfgrasses would be valuable management tools. The objective of this study was to evaluate the capacity of a hand-held chlorophyll meter (SPAD-502) to provide a relative index of chlorophyll concentrations, N concentrations, and visual quality in St. Augustinegrass [Stenotaphrum secondatum (Walt.) Kuntze]. Two experiments were conducted in a greenhouse in 1998 to evaluate the utility of SPAD readings. Established pots of 'Floratam' were subjected to weekly foliar Fe treatments at Fe rates of 0 and 0.17 kg · ha-1 for 4 weeks. Six weekly nitrogen fertilizer treatments were applied in the form of ammonium sulfate at N rates of 0, 5.75, 11.5, 17.25, and 23 kg · ha-1 for 4 weeks. Greenhouse SPAD readings were not affected by Fe treatment, but N treatments resulted in differences in SPAD readings, visual quality, and chlorophyll concentrations. The readings were positively correlated with chlorophyll concentrations (r2 = 0.79), visual ratings (r2 = 0.74), and total Kjeldahl nitrogen (TKN) (r2 = 0.71). Readings taken from field-grown 'Floratam', 'Floratine', and 'Floralawn' St. Augustinegrass were poorly correlated (r2 < 0.63) with chlorophyll concentrations and TKN. Unless future techniques improve dependability of the SPAD meter under field conditions for measuring chlorophyll and N concentration of a stand of turfgrass, the usefulness of such readings for the management of St. Augustinegrass seems limited.