Rooting of Warm Season Grasses Inhibited by Increased Soil Bulk Density.

Warm-season grasses are frequently installed as sod at new construction sites where heavy equipment may have increased the soil bulk density of the planting area.  The affect of soil bulk density (SBD) on sod rooting during a six-week establishment period was tested for ‘Argentine’ bahiagrass (bahia), ‘Floratam’ St. Augustinegrass (StAug), and ‘Empire’ zoysiagrass (zoysia).  In a repeated study, the sod was grown in clear rooting tubes, and the deepest root depth was recorded daily.  The bulk density of the field soil filled tubes was 1.4 or 1.6 g cm^-3 (SBD 1.4 or SBD 1.6)  The repeated study occurred fall 2010 and summer 2011.  In the fall, the root elongation rate (RER) was 13.9, 13.0, and 13.8 cm d^-1 for bahia, StAug, and zoysia, respectively in SBD 1.4 , and RER was 9.9, 7.1, and 7.4 cm d^-1 for the same grasses in SBD 1.6.  In the summer, the decrease in RER was more dramatic due to the increased growth at the lower SBD.  The RER for bahia was 23.4 and 9.6, for StAug was 25.6 and 9.6, and for zoysia was 23.7 and 12.5 cm d^-1 in the SBD 1.4 and SBD 1.6, respectively.  Total root length (TRL) for all grass species declined with depth and increased compaction in both seasons.  In the winter, SBD had little effect on TRL in the upper 20 cm (5 to 16% reduction), but in the lower 20 cm, TRL was reduced by 51 to 65%.  The most dramatic result occurred during the summer. when increased SBD reduced TRL at the 0 to 30 cm depth by 55 to 67%, but from 30 to 40 cm depth the reduction in TRL was 140%.  Rooting of warm season grass sod was strongly inhibited by increased soil bulk density during summer months.