Nitrogen Source and Rate Affect Color Retention On Warm Season Grasses Under Saline and Drip Irrigation.

Nitrogen fertilization helps to enhance turf quality during the growing season and can shorten the dormancy period of warm season grasses. A study was conducted at New Mexico State University to investigate the effect of nitrogen fertilization on fall color retention and spring green-up in established seashore paspalum (Paspalum vaginatum) ‘Sea Spray’ and bermudagrass (Cynodon dactylon) ‘Princess 77’ turf. Two nitrogen rates, 10 and 20 g m^-2year^-1 on Sea Spray  and 20 and 30 g m^-2year^-1 on Princess 77 from 5 different fertilizer sources [urea liquid, urea granular, Burley green^™, CoRoN^®, and a granular slow release (20-4-8)] were applied. Plots were irrigated with either potable (370 ppm) or saline (1600 ppm) water from sprinkler or subsurface drip irrigation systems. Digital images, Normalized Difference Vegetation Indices (NDVI), and visual quality ratings were taken bi-weekly. At the end of the growing season, stolons and rhizomes were collected to determine carbohydrate and starch contents. Urea granular and slow release urea provided the greatest color retention for both grasses in mid November. When data were averaged over both water qualities and all fertilizer types, sprinkler irrigated bermudagrass and seashore paspalum fertilized with 30 g N/m²/year and 20 g N/m²/year respectively exhibited greatest color retention in November. All other treatment combinations (turf species, irrigations system, and N-rate) showed less color retention. Sugar analysis of stolons and rhizomes revealed that rhizomes accumulated more starch, glucose and sucrose than stolons. Fertilizer type and amount affected starch and carbohydrate content in rhizomes differently than in stolons. Moreover, drip irrigated plots showed less sucrose accumulation than sprinkler irrigated plots.  Sucrose content in rhizomes of bermudagrass fertilized at 30 g N/m²/year was significantly correlated to fall color (r = 0.64)  These results suggest that nitrogen management is important to ensure good fall color retention in the transition zone