Photoperiod Effects upon Shoot Growth and Color of Bermudagrass Fertilized with Slow-release Nitrogen Sources

Abstract

Total plant biomass, shoot growth rate, and the periodicity in shoot growth and color of hybrid bermudagrass [Cynodon dactylon (L.) Pers. x C. transvaalensis Burtt-Davy 'Tifgreen'] in response to slow-release fertilizer N sources, rates, and application frequencies were studied in two, 120-day greenhouse studies. Plugs were planted in plastic cylinders filled with a growing medium of 93 sand : 7 peat moss (w/w). The first experiment was completed under progressively increasing photoperiod (13.1 to 14.9 hours) typical of the long-day requirements for bermudagrass growth. The second experiment occurred under progressively decreasing photoperiod (13.7 to 10.7 hours) representative of autumnal growing conditions and declining growth and N demand. Urea (URE), sulfur-coated urea (SCU), and hydroform (HYD, methylene urea polymers) were broadcast at N rates of 100 or 200 kg·ha -1 and at frequencies of 20 or 40 days. Bermudagrass was clipped at 3-day intervals and the average daily clipping growth rate (increase in shoot dry matter; DM) reached a maximum of 11.5 g·m-2 per day. Use of the least soluble source, HYD, produced the lowest total clipping DM, and at low HYD rate and frequency, leaf color intensity was frequently below the accepted standard of 7, in the scale from 1 "tan" to 9 "dark green". A greater responsiveness of bermudagrass to N rate and application frequency (increased clipping growth rate and color intensification upon N application) occurred under increasing photoperiodic conditions as compared to decreasing photoperiodic conditions. Both clipping growth and color changed cyclically through time and mainly under long-day photoperiod (>12 hours), with greater oscillation at longer fertilization interval (40 days). With either SCU or URE, at low N rate and frequency (total N application of 0.25 g·m2 per day), clipping growth rates were above 4 g·m-2 per day, and turf color was at or above the minimum quality standard through most of the growing period. Higher total SCU and URE application rates, previously shown to increase N leaching losses in these experimental conditions, produced significantly more clipping growth and did not appear to intensify color sufficient to warrant the increased risk of N loss.