Nitrogen and Phosphorus Nutritional Influence on Bentgrass–Annual Bluegrass Community Composition

Abstract

This study evaluated the effect of N and P fertilization on the change in species composition of a bentgrass ( Agrostis spp.) and annual bluegrass ( Poa annua L.) turf. Species composition was determined by a square grid method and visual estimate of percent bentgrass and plant separations. Bentgrass population significantly increased in those areas from which N was withheld for 3 years compared to areas that were fertilized with N. Phosphorus fertilizer treatments had no effect on species composition. Except for one of the three ratings made in 1982, turf quality was not significantly reduced by withholding N. Quality had begun to improve by 1984 on the no-N plots compared to the N-fertilized plots. This change was associated with increased bentgrass population. There was a significant correlation between the square grid and visual estimate method used to evaluate the change in species composition in 1982, 1983, and 1984 ( r = 0.84, 0.87, and 0.88, respectively). Although the N content of the leaf tissue was greater in the bentgrass tissue compared with annual bluegrass, leaf tissue concentrations were within or above the sufficiency range for grasses. This study has shown that withholding N fertilization in some years under certain conditions gives bentgrass a competitive advantage over annual bluegrass without lessening turf quality.