Efficient Irrigation for Recreational Turf in the Cool-Humid Northeast: II. Summer Rooting.

Deep rooting improves acquisition of water and nutrients and decreases irrigation requirements by lengthening the irrigation cycle. Excessively close height of cut (HOC) and nitrogen (N) fertilization can inhibit rooting depth especially in summer for cool-season turfgrass. The objective of this study was to assess rooting by soil depth comparing golf species (creeping bentgrass, CBG, Agrostis stolonifera L. ‘Memorial’) maintained as green and fairway turf with sports grass species (Kentucky bluegrass, KBG, Poa pratensis L. ‘Touchdown’ and perennial ryegrass, PRG, Lolium perenne L. ‘Exacta’). Studies were initiated in 2010 at the Joseph Troll Turf Research Center, South Deerfield, MA. Species (SP) main plots were arranged as a complete factorial with two N levels, 98 and 196 kg N ha-1 yr-1, with four replicates arranged as a RCB. The 196 kg N plots received 49 kg N ha-1 in summer using 82% of the N from slow release. All SP by N main plots were split according to two HOC with sports grass maintained at 31.25 and 62.5 mm and golf main plots were mowed at 3.125 (green) and 9.375 (fairway) mm. Rooting was assessed in early July and late August in 2010 and 2011 at four soil depths, 0 to 10 cm (SD1), 10 to 25 cm (SD2), 25 to 45 cm (SD3), and 45 to 65 cm (SD4). Percent of total root mass by soil depth when averaged across year and month was 85.3% (SD1), 11.3% (SD2), 2.9% (SD3) and 0.5% (SD4). Little effect on rooting within SP was observed between low and high HOC and between low and high N. At SD2 when averaged across all SP, 25% more rooting was observed with higher HOC in 2010 while in 2011 33% more rooting was observed with low N treatments. In 2010, rooting of SP by soil depth was: KBG>PRG=CBG (SD1), PRG>KBG>CBG (SD2), PRG>KBG=CBG (SD3), and KBG=PRG=CBG (SD4). In 2011, rooting of SP by soil depth was: KBG>PRG=CBG (SD1), PRG=KBG>CBG (SD2), PRG=KBG=CBG (SD3), and KBG=PRG=CBG (SD4). In 2010 and 2011 a SP X N X HOC interaction was observed at SD4 and SD3, respectively. In 2010, unfertilized CBG fairway in summer exhibited rooting at SD4 equal or greater than KBG and other CBG treatments. In 2011, CBG showed rooting potential at SD3 equal to KBG and PRG treatments. CBG was able to maintain rooting under golf HOC equivalent to some tall grass SP under similar N levels.