Effect of Nitrogen Source, Rate, and Timing on Growth and Carbohydrates of Merion Bluegrass

Nitrogen fertility stimulates turfgrass growth and, therefore, reduces carbohydrates. Turfgrass response to stresses (heat, drought, and disease) is improved when carbohydrates are highest. This study was conducted to determine the effect of different nitrogen sources, rates, and time of application on the growth and soluble carbohydrate content of ‘Merion’ Kentucky bluegrass (Poa pratensis L.). During 1971 and 1972 Merion was fertilized with urea, Uramite (ureaformaldehyde), Milorganite (activated sewage sludge), IBDU (isobutylidine diurea), and Urex (extruded urea-paraffin matrix) at different rates and application dates. Growth was measured weekly and total nonstructural carbohydrate content every 2 weeks. Growth stimulation from slow release sources reduced carbohydrates when temperatures were high; improved growth uniformity resulted from split applications of these materials. Urex stimulates early growth more than other slow release sources, resulting in a severe depletion of carbohydrates prior to warm weather. Multiple applications of Urea and Milorganite gave more uniform growth throughout.ithe season with less fluctuation of carbohydrates than other sources. Nitrogen fertility, moisture, and temperature, collectively, interacted with the metabolism of Merion, their effects being readily reflected in the total nonstructural carbohydrate content. Periodic cool spells during the season offset reductions in carbohydrates caused by nitrogen fertilization, regardless of the fertilizer source. However, prolonged warm spells occur along the southern boundary of cool-season turIgrass adaptation, and we conclude these temperature stresses could have severe effects, particularly if the stresses coincide with nitrogen induced carbohydrate depletion.