Polymer Coated Urea in Kentucky Bluegrass: Optimal Timing and Rate of Application.

Nitrogen (N) is commonly over-applied in urban environments resulting in increased water and air pollution, maintenance costs, squandered natural resources, and landfill waste. Polymer coated urea (PCU) has proven to be excellent for mitigating N pollution, but rate and timing parameters need further study. Two field Kentucky bluegrass (Poa pratensis L.) locations in Provo, UT, USA were evaluated weekly for height and health/greenness (NDVI) during 2014 and 2015. Treatments included: 1) zero N control, 2) full rate—urea split applied monthly (April to November), 3) full rate—single PCU application applied in spring, 4) full rate—single PCU application in late summer, 5) full rate—two evenly split applications with half applied in spring and half in late summer, 6) 75% rate—two evenly split applications, 7) 50% rate—two evenly split applications, and 8) full rate—three evenly split applications in spring, late summer, and late fall. The full rate was 19.5 and 29.3 g m^-2 for the sandy loam and sand locations, respectively; with 33% of all fertilized treatments applied as ammonium sulfate and the remainder applied as either coated (PCU) or uncoated urea. All fertilized treatments resulted in significant increases in NDVI and height. Two and three applications of PCU had nearly identical growth and health/greenness as compared to the “ideal” of urea applied monthly. The single PCU applications were unacceptable due to excessive growth shortly after application and poor NDVI at the opposite end of the season. The treatment with two evenly split PCU applications showed no significant difference between the full and 75% rates, but a 50% reduction showed significantly reduced height and NDVI. Further work is needed to evaluate the long-term impacts of a reduced PCU rate, as well as finding ways to effectively apply with a single application.