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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.

Root distribution in turfgrass systems influences drought tolerance and resource competition with undesirable species. We hypothesized that spatial localization of phosphorus (P) supply would permit manipulation of turfgrass root distribution. To test this hypothesis, creeping bentgrass (Agrostis stolonifera L.) plants were exposed to localized P supply in two experiments. The first experiment split the root zone horizontally into two different growth tubes and the second used alumina-buffered P (Al-P) to localize P availability deeper within a continuous root zone. In the horizontally split root zones, heterogeneous P availability led to no difference in shoot growth compared with uniform P availability. Root proliferation was greatest in the growth tube with available P compared with the growth tube without P. The use of Al-P, regardless of its spatial distribution, doubled root-to-shoot ratios compared with soluble P. Much of the increase in the ratio was accounted for by reduced shoot growth. Use of Al-P increased rooting deeper in the root zone, especially when the Al-P was mixed only in the lower portion of the root zone. Our results are consistent with the hypothesis that root distribution of creeping bentgrass can be manipulated by spatial localization of P supply in the root zone and indicate that relative biomass allocation to roots and shoots may be manipulated with buffered P sources.

Two complementary greenhouse studies were conducted to examine the effects of different root zones and fertilization regimes on ‘SR7200' velvet bentgrass (Agrostis canina L.) and L-93 creeping bentgrass (Agrostis stolonifera L.). In the first study, in which only velvet bentgrass was studied, peat content in the root zone mixture contributed significantly to initial establishment of this species and high seeding rates increased cumulative shoot dry weight early in establishment but became less significant as the turfgrass matured. Higher phosphorus rates contributed to increased cumulative shoot dry weight over the first 4 weeks of the experiment. Nitrogen rate was the most significant factor positively affecting both cumulative shoot dry weight and turfgrass quality. In the second experiment with both velvet bentgrass and creeping bentgrass, nitrogen rate significantly increased turfgrass quality when measured at Week 5, halfway through the experiment. Over time, however, turf growth and quality were negatively impacted in both species with increasing nitrogen rates. Root zone composition had a significant effect on initial establishment of both bentgrasses with greater peat content leading to higher quality early on. Cumulative shoot dry weight increased with increasing nitrogen rate but at higher rates, there was a concomitant decrease in root production.