There is growing concern that excess nitrogen (N) is being applied to lawns and may be contaminating groundwater. The purpose of this two-year field study was to evaluate current lawn N recommendations and investigate alternative N programs for three cool-season lawn species grown in Indiana: Kentucky bluegrass, turf-type tall fescue, and perennial ryegrass. Eight N programs were designed ranging from 0 to 196 kg N ha-1 yr-1 applied as urea, sulfur coated urea or a combination depending upon season. Turfgrass N response was evaluated using dry matter yields (DMY), leaf tissue N content, and canopy greenness. Visual ratings for turfgrass quality and disease incidence and severity were also regularly recorded. Soil N was monitored using suction cup lysimeters, 45 cm below the soil surface, and by KCl extractions. As expected, DMY increased with N fertilization, especially for turf-type tall fescue. Additionally, leaf tissue N content increased with N rate, ranging from 2-5 %. Plots receiving multiple fall N applications retained their green color longer into the late-fall and generally had faster spring green-up except for Kentucky bluegrass. During July of both years, dollar spot severity was worst in perennial ryegrass, regardless of N program and Kentucky bluegrass receiving low, < 74 kg N ha-1 yr-1 N rates. Soil N levels were generally very low (< 1.5 ppm) except for under Kentucky bluegrass during spring green-up (April-May) where nitrate levels in some plots exceeded 10 ppm . For a moderate quality lawn, turf-type tall fescue or Kentucky bluegrass fertilized at 123 kg N ha-1 yr-1 applied in three annual applications is sufficient with minimal risk of N leaching.
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