Absorption and Metabolism of Foliar-Applied Nitrogen Sources on Creeping Bentgrass Under Greenhouse Conditions.

Absorption of foliar-applied nitrogen is complicated since the absorbed forms including a cation as NH₄⁺, an anion as NO₃^-, and organic forms as urea and amino acids. A project was conducted at Clemson University from January 2014 to May 2014 on ‘Crenshaw’ creeping bentgrass [Agrostis stolonifera L. var. palustris (Huds.) Farw.] to investigate leaf N metabolism of different N sources at a molecular level, urease enzyme activity (UEA) and total amino acids (TAA), under greenhouse conditions. Six different N sources, including Urea, NH₄Cl, NaNO₃ and three commercially available N products UMAXX, UFLEXX, and HYDREXX+Urea, were foliar-applied at 0.98 g N m^-2 with a spray chamber. Leaf tissue was harvested at 3, 6 and 9 weeks after application. Tissue analysis included UEA, TAA and total N content (TNC). Turf Quality (TQ) was recorded weekly throughout the study. N sources affected UEA at week 3 and week 6, but had no effect for TAA and TNC. UMAXX, UFLEXX, HYDREXX+Urea and Urea had higher UEA than other treatments at week 3. At week 6, Urea had lower UEA than UMAXX and HYDREXX+Urea, but higher than other N sources and control. All N sources showed higher TQ compared to control in the first two weeks, but Urea, NH₄Cl and NaNO₃ had a gradually decreased TQ compared to UMAXX, UFLEXX, and HYDREXX+Urea, which revealed a more consistent TQ throughout the study. The results indicated that a higher turf quality may be benefitted by a more consistent release of N and a higher level of N metabolism.