Golf Course Management

DEC 2018

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68 GOLF COURSE MANAGEMENT 12.18 August) of 2014, 2015 and 2016, the two irrigation treatments were applied by hand watering individual plots twice a week using calculated amounts from daily ET o rates from an on site weather station (Figure 3). When the rainout shelter was not activated (September May), the plots all received ad equate irrigation (≤ 0.5 inch/week) and any occurring precipitation. We applied three fertilizer treatments: 1) a controlled released, polymer coated urea (PCU) (41 0 0; 90 day release, Polyon, Koch Agronomic Services) applied once at the begin ning of summer for a total of 2 pounds nitro gen/1,000 square feet/year (97.6 kilograms/ hectare); 2) a quick release, urea (46 0 0; rive Branded Fertilizer, Mears Fertilizer) applied at a rate of 1 pound nitrogen/1,000 square feet (48.8 kilograms/hectare); at the be ginning of summer and again at mid summer for a total of 2 pounds nitrogen/1,000 square feet/year; and 3) an unfertilized "control" re ceiving no nitrogen fertilizer. After fertiliza tion, plots were individually hand watered as described above with respect to the corre sponding irrigation treatment to incorporate Figure 5. A nitrous oxide measurement date during the summer using static chambers mounted on base collars in the soil. A single measurement date required 20 hours, which consisted of evacuating collection vials, collecting ancillary measurements and nitrous oxide measurements, and then transporting the vials back to the lab for analysis with a gas chromatograph. fertilizer into the soil and reduce ammonia (NH 3 ) volatilization. We measured soil surface nitrous oxide fluxes from October 2014 through October 2016 using static, vented polyvinyl chloride chambers and gas chromatography (Figures 4, 5). Fluxes of nitrous oxide were measured at least once weekly during the growing season from May through September and once every two to four weeks during winter dormancy from October through April. Measurements were more frequent surrounding fertilization events in the summer, such as one, three, five and seven days after nitrogen fertilization. Ancillary measurements of soil moisture, air and soil temperature, soil NO 3 and NH 4 , and visual turf quality were also collected during the study. Summer nitrous oxide emissions Overall, the highest nitrous oxide fluxes and majority of nitrous oxide emissions oc curred during summer, which is in agreement with previous research (4, 5, 8). Presumably, this is because of higher soil temperatures (data not shown; see reference 3 for more in formation), which stimulate soil microbial ac tivity. However, in the case of warm season grasses such as zoysiagrass, nitrogen fertiliza tion in the transition zone occurs during the summer, and nitrogen fertilization contributes significantly to nitrous oxide emissions (8, 9). erefore, in terms of nitrous oxide emissions, it is important to examine summer irrigation and nitrogen management practices. When plots were irrigated (during the two summers), cumulative nitrous oxide emissions were reduced by 6% with less irrigation (33% ET o ) (Table 1). is demonstrates that less irrigation reduces nitrous oxide emissions and, therefore, reducing irrigations not only saves water, but also reduces greenhouse gas emis sions. In terms of nitrogen fertilization effects, cumulative nitrous oxide emissions over the two summers were highest in plots fertilized with quick release urea, lowest in unfertilized plots and intermediate in PCU plots. In both fertilized treatments (urea and PCU), reducing irrigation also reduced ni trous oxide emissions (Table 1). Interestingly, emissions were always higher with urea than with PCU, regardless of irrigation rate. is indicates that using PCU reduces nitrous oxide emissions more than reducing irrigation in urea fertilized plots. Irrigation level did not affect nitrous oxide emissions in unfertilized plots (Table 1), but over the two summers, nitrous oxide emis sions were as low in PCU at low irrigation as they were in unfertilized plots at both irriga tion levels. is is significant because it in dicates the combination of fertilization with PCU and less irrigation could reduce nitrous oxide emissions to levels similar to those found in unfertilized turfgrass. e primary mechanism that produces lower nitrous oxide emissions in plots treated with PCU than in those treated with urea seems to be related to fertilization events. Namely, after application of quick release urea fertilizer, there were large spikes in ni trous oxide fluxes, but these spikes in fluxes were negligible after application of controlled release (PCU) nitrogen fertilizer, which was less affected by soil conditions (for example, soil moisture) at time of application (3). Over all, reductions in nitrous oxide emissions are likely a result of slower nitrification and de nitrification processes in soils associated with less irrigation and controlled release forms of nitrogen fertilization.

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