Little knowledge exists regarding root distribution of creeping bentgrass (Agrostis stolonifera) and annual bluegrass (Poa annua) in root zones of golf course putting greens. To compare root distribution between these species, three experimental cultivars of greens-type annual bluegrass and two commercial cultivars of creeping bentgrass ('Penncross' and 'Penn A-4') were established on an experimental golf green and managed under two nitrogen (N) fertility levels (195 and 65 kg N/ha/year) over a 2-year period. Creeping bentgrass had two and three times the total root mass compared with annual bluegrass during the first and second years of the experiment, respectively. At soil depths of 3-12 cm and below 12 cm, creeping bentgrass had three to four times the root mass compared with annual bluegrass at various times during the experiment. During the first year of the experiment, both species exhibited greater than 50% decrease in total root mass from June to August. During the second year, creeping bentgrass total root mass decreased 10% to 15% and annual bluegrass total root mass decreased 25% to 30% over the same period. Of the two bentgrasses, 'Penn A-4' creeping bentgrass exhibited greater total root mass only in the second year; however, 'Penn A-4' exhibited greater root mass than 'Penncross' below 12 cm in both years. Creeping bentgrass cultivars showed greater root mass below 12 cm at 65 kg N/ha/year compared with 195 kg N/ha/year on some sampling dates in both years. Annual bluegrass cultivars showed no change in any root mass parameters in response to N rates (data not shown), but specific root length (SRL) of annual bluegrass increased under the 65 kg N/ha/year rate compared with the 195 kg N/ha/year rate, whereas SRL of creeping bentgrass was similar at both N rates. Tiller densities of both species increased under the 195 kg N/ha/ year rate. 'Penn A-4' exhibited higher tiller densities than 'Penncross' throughout the experiment and at times was equivalent to the tiller densities of the annual bluegrass cultivars. These results suggest that although creeping bentgrass increases root mass deeper in a putting green root zone mix at lower N rates (65 kg N/ha/year), annual bluegrass exhibits plasticity in specific root length in response to different N rates.
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