Foliar and Granular Nitrogen Fertilization of Bentgrass

Abstract

Creeping bentgrass, (Agrostis stolenifera L.), is the most widely used cool-season turfgrass for golf course putting greens. Creeping bentgrass is a fine-textured, stoloniferous, perennial with exceptional cold tolerance. Maintaining creeping bentgrass in the hot humid climate of the Southeast poses challenges for golf course superintendents in the summer, when drought, heavy traffic and low mowing height create stress. Although newer cultivars have been developed to cope with the climate in the South, maintenance of bentgrass still requires frequent and intensive inputs to maintain acceptable turf. Fertilization is a key cultural practice in order to promote a healthy turf. Foliar fertilization of turfgrass may provide advantages over granular application, including rapid turf response to the foliar nutrients, reduced fertilizer input, minimized potential losses by leaching and runoff, and the advantage of applying low rates of fertilizer when turf is under stress. Nitrogen is the main nutrient in a turfgrass fertilization program, and is responsible for maintaining turfgrass shoot density, recovery from stress, shoot growth rate, color and quality. Previous research has shown that foliar applied N is absorbed by transcuticular pores, has low volatility, and that time of day of application has little effect on N uptake. However, little is known about appropriate foliar rates of N for maintenance of bentgrass in the humid South, or timing of that N in conjunction with irrigation. The research objectives of this study were to examine the combined and separate effects of foliar N rate and timing of irrigation on the color, quality, shoot density, root growth and carbohydrate status of a creeping bentgrass putting green. The study was a two-year experiment conducted at the Auburn University Turfgrass Research Unit (TGRU), located in Auburn, AL. Treatments were 4 rates of N (0.5, 1.0, 2.0 and 4.0 g m-2) and 3 methods of fertilizer application (granular watered in, foliar watered in, and foliar not watered in). In general, N rate most affected turf color and quality, with color typically increasing as N rate increased, regardless of the method of application. The only exception to this was in summer, when high rates of foliar N without a following irrigation created turf leaf-tip burn, lowering quality. Overall, N applied as a foliar treatment provided excellent turf quality, but the highest one time application of 4.0 g m-2 should be applied as a split application within the month.