Influence of nitrogen rate and form on quality of putting greens cohabited by creeping bentgrass and annual bluegrass

Of the essential nutrients, N fertility generally influences golf course putting green (PG) quality and growth rate most significantly. Despite considerable field research on N fertility of PGs, results interpretation and transfer to practice is complicated by various influential factors; including unrepresentative mowing heights and/or frequency, varying irrigation water quality, undeclared composition of mixed swards, withdrawn cultivars, and/or use of temperature-dependent organic fertilizer sources. A 2-yr field study was initiated in 2003 at University Park, PA, to evaluate the influence of soluble N fertilizer source and rate on qualitative and nutritional parameters of a mature, primarily surface-drained, "push-up" PG cohabited by 'Penn A4' creeping bentgrass (Agrostis palustris Huds.) and annual bluegrass (Poa annua L.). Using an array of soluble N form quotients (NH₄-N/ NO ₃-N), split applications of annual N fertilizer rates ranging from 69 to 402 kg ha^-1 were sprayed every 15 ± 4 d, April to October. Putting green growth, color, N uptake (NUP), and leaf N, K, Ca, Mn, Cu, and Zn increased directly with N rate, while plots receiving N rates in excess of 244 kg ha^-1 yr^-1 demonstrated acceptable PG quality and tissue nutrient concentrations. However, N rates >244 kg ha^-1 yr ^-1 containing >50% NH₄-N significantly enhanced shoot growth, color, NUP, leaf Mn, P, and Mg levels, when compared to equal rates containing ≥50% NO₃-N. Frequent fertilization with NH ₄-N at annual rates >244 kg ha^-1 maximized canopy color and most tissue nutrient levels of a mature creeping bentgrass/annnal bluegrass cohabited PG growing on a neutral, fine-textured soil.