Less Frequent Irrigation Increases Rooting Depth of Some Warm-Season Turfgrasses During Establishment.

Deeper, less frequent irrigation is a common suggestion for stimulating deep rooting in turfgrasses.  This suggestion was examined in two studies using ‘Argentine’ bahiagrass (Paspalum notatum), ‘Floratam’ St. Augustinegrass (Stenotaphrum secundatum) and ‘Empire’ zoysiagrass (Zoysia japonica).  Sod from each species was planted into clear acrylic columns (15 cm dia x 48 cm) and grown under greenhouse conditions.  The study was a completely randomized design with 3 species x 2 irrigation frequency treatments (280 ml wk^-1 or 40 ml d^-1) x 5 replicates (30 total columns).  The deepest root was measured daily.  After 6 wks, bahiagrass and St. Augustinegrass maximum rooting depths were increased with weekly irrigation by 19% and 60%, respectively, while zoysiagrass was unchanged.  Between March 2011 and December 2012, the same three species were grown in 3 m x 3 m plots, randomized within 3 irrigation blocks (12 total plots).  The 3 irrigation treatments were:  (I1) 2 d wk^-1 following the University of Florida extension recommendations for homeowners, (I2) application at the onset of visual wilt (per species), and (I3) no irrigation.  Root cores (5-cm dia x 60 cm) were collected in triplicate from each plot during October 2011, August and October 2012.  Bahiagrass and zoysiagrass root mass increased (130% and 145%) between 2011 and 2012, but the increase in St. Augustinegrass root mass (60%) was not significant.  Bahiagrass root mass in the upper 30 cm increased under I2 versus I1, and further increased under I3 v I2, but St. Augustinegrass and zoysiagrass root mass was not affected.  Under controlled conditions, both bahiagrass and St. Augustinegrass had increased rooting depth with less frequent irrigation, with no impact on zoysiagrass.  In the field, only bahiagrass rooting depth was increased by less frequent irrigation.