Golf Course Management

DEC 2018

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70 GOLF COURSE MANAGEMENT 12.18 Annual and total cumulative N 2 O emissions For overall cumulative nitrous oxide emis sions, the type of fertilizer had a significant ef fect in both years and during the entire two year period, but the amount of irrigation did not have a significant effect during the entire two year period (Table 1, Figure 6). e over all lack of effect of irrigation was contrary to results previously mentioned for cumulative summer nitrous oxide emissions. is was likely due to the absence of irrigation treat ments during the remainder of either year (that is, the "offseason," when all plots received identical irrigation and precipitation for nine months of the year), which diluted the over all effects of the irrigation treatments over the entire study. Conversely, the fertilizer treat ments, which were also applied only during the summer, had more frequent and more pro nounced differences between treatments than the irrigation treatments (data not shown), which led to annual cumulative differences. Over the entire two year period, total cu mulative emissions of nitrous oxide were in creased by 38% with urea fertilization and by 11% with PCU fertilization, compared with unfertilized turf (Figure 6). Compared with urea, nitrous oxide emissions were reduced by 20% using PCU treated turf and by 28% in unfertilized turf in this study. e range of emissions (1.82 to 2.85 kilograms N 2 O N/ Source of variation Nitrous oxide ( N 2 O-N kg/ha) emissions Total summer periods Total off-season periods Combined total for 2-year period Fertilizer Urea 3.59 a † 2.03 a 5.62 a Polymer-coated urea (PCU) 2.53 b 1.97 a 4.50 b Unfertilized (UF) 2.28 c 1.78 b 4.06 c Irrigation ‡ Medium 2.88 a 1.89 4.77 Low 2.71 b 1.97 4.68 Fertilizer × irrigation Urea × Medium 3.68 a 1.95 5.63 Urea × Low 3.50 b 2.11 5.61 PCU × Medium 2.68 c 1.96 4.64 PCU × Low 2.37 d 1.99 4.36 UF × Medium 2.29 d 1.75 4.04 UF × Low 2.27 d 1.80 4.07 † Within source of variation, means in column with different letters are significantly different. ‡ Medium irrigation level was 66% evapotranspiration (ET o ) replacement, and low irrigation level was 33% ET o replace- ment. Irrigation treatments were applied only during the summer periods. Table 1. Analyses of fertilizer main effect, irrigation main effect, and fertilizer × irrigation interaction on two-year total cumulative nitrous oxide emissions for the summer periods (June-August), offseason period (September-May), and the combined total of the entire two-year period. 5.0 4.0 3.0 2.0 1.0 Cumulative nitrous oxide emissions (kilograms N/hectare) 302 155 197 278 158 202 277 of 2014 of 2015 of 2016 Day of year, 2014-2016 Analyses of fertilizer and irrigation on nitrous oxide emissions Figure 6. Cumulative fluxes of N 2 O-N over a two-year period from zoysiagrass treated with polymer-coated urea, no fertilizer (unfertilized), and urea. Dashed vertical lines at day of year (DOY) 155 in 2015 and DOY 158 in 2016 represent June fertilization (urea at 1 pound nitrogen/1,000 square feet and polymer-coated urea at 2 pounds nitrogen/1,000 square feet) and at day of year 197 in 2015 and DOY 202 in 2016 represent July fertilization (second urea application at 1 pound nitro - gen/1,000 square feet). At the end of the first year and at the end of the two-year study, means with different letters are significantly different. Cumulative fluxes of nitrous oxide

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