Effect of Mowing Frequency on Clipping Decomposition and Nitrogen Return.

Evaluating nitrogen fate following clipping decomposition may allow us to improve nitrogen-use efficiency (NUE) in turfgrass systems.  The objective of this study was to evaluate the effect of mowing frequency on N mineralization and NH₃ volatilization from decomposing ‘TifTuf’ bermudagrass (Cynodon dactylon x C. transvaalensis) clippings applied to the soil surface.  Field trials were established at two University of Georgia research facilities in Athens, GA during the summer of 2015.  Plots measured 1.6 x 1.4 m and were arranged within a randomized complete block design with four replications.  We had four treatments, mowing at 3, 7, 10, or 14-day intervals using a Honda Twin-Blade 3-in-1 rotary push mower set to a height of 5.7 cm to simulate home lawn height.  Clippings were harvested 40 days after trial initiation and weighed to determine total biomass output per plot (g/m²).  Soil was collected from each location, packed into 5.08-cm diameter polyvinyl chloride cylinders and adjusted to -0.33 MPa.  Grass clippings were air-dried for 48 h and placed directly onto the soil surface in each cylinder in quantities proportionate to in situ area density.  For the duration of the 90-d incubation period, each cylinder was sealed in a 1-L glass container and stored in a controlled environment chamber at a constant temperature of 28 °C.  Cumulative evolved NH₃ was trapped with 0.1 H₂SO₄, and inorganic N in tissue extracts and soil were analyzed after 90 d.  Preliminary results indicate that mowing frequency may be an important factor in controlling % NH₃ volatilization from decomposing grass clippings and one pathway to improving overall NUE in turfgrass systems.