The effect of Trinexapac Ethyl and three Nitrogen sources on creeping bentgrass (Agrostis stolonifera) grown under three light environments

Shade stress on creeping bentgrass (Agrostis stolonifera) causes elongation of leaves, reduced energy availability for growth and lower levels of disease resistance resulting in poor quality putting surfaces. Decreased quantity or photosynthetic photon flux density (PPF) and quality or the red:far red light ratio (R:FR) of light affects the morphology of turfgrass plants by increasing production of giberellic acid and reducing available non-structural carbohydrates. The object of the study was to determine which source of nitrogen (N) is best suited to retaining turfgrass quality in shade and to see if the plant growth regulator trinexapac-ethyl [4-(cyclopropyl-α-hydroxy-methylene)-3,5-dioxo-cyclohexane carboxylic acid ethyl ester] (TE) (Syngenta AG, Switzerland) can improve density and combat the loss of surface quality of bentgrass under tree shade. Field studies were conducted on ‘Penncross’ creeping bentgrass (Agrostis stolonifera) in Columbus, in 2006, and 2007. Under three light environments: full sun (FS), reduced R:FR (DS), and reduced PPF (NS). Light reduction was >90% in both shade areas and the R:FR ratio was .38 in the DS area, 1.28 in NS, and 1.29 in FS. The three N treatments included (NH₂)₂CO, Ca(NO₃)₂ and (NH₄)₂SO₄ foliarly applied weekly at a rate of 0.43g m^-2 with or without TE applied bi-weekly at 0.3975 L ha^-1.

Chlorophyll content, along with non-structural carbohydrates, flavonoids, turf canopy color, dry matter and canopy densities were measured. There were no differences in soluble carbohydrate levels between treatments. Chlorophyll levels varied between TE treated and non-treated areas. Applications of (NH2)2CO consistently resulted in higher content of N15 in turfgrass plants also but there was no effect in nitrogen uptake kinetics due to light environment differences.

TE had a negative impact on quantities of flavonoids. There was variation between the N treatments in relation to dry matter and carbohydrate content. (NH2)2CO in combination with TE provided the best visual quality surface as the season progressed. TE was effective in reduced PPF conditions and R:FR conditions which would indicate it as a possible product for use in shade management of creeping bentgrass Agrostis stolonifera. It was equally efficient in both light environments suggesting that prior shade research using NS is relevant to shade management in private industry. There was not a strong indication as to a preferred source of N.(NH₂)₂CO had positive impacts on total chlorophyll content.