This paper focuses on the causes of zonationon agricultural land affected by secondary salinitybetween two halophytic grasses, puccinellia(Puccinellia ciliata Bor. cv. Menemen) and tall wheatgrass(Thinopyrum ponticum (Podp.) Z.-W. Liu & R.R.-C. Wang cv. Tyrrell). We hypothesized that thedifferences in zonation of puccinellia and tall wheatgrasswere caused primarily by differences in thetolerance of these two species to waterlogging undersaline conditions. This hypothesis was tested by conductingexperiments in the field and in the glasshouse inirrigated sand cultures. At a saltland field site, locationsdominated by puccinellia had ECe values that wereconsistently higher (11–12 dS/m in early spring, and5–9 dS/m in late summer) than locations dominated bytall wheatgrass. However locations dominated bypuccinellia also had a watertable that was shallower(0.07–0.09 m in the high rainfall season; 0.11–0.13 min the low rainfall season) than locations dominated bytall wheatgrass. In the glasshouse both species hadsimilar growth responses to salinity under drainedconditions, with a 50% decrease in shoot dry mass(DM) at ∼300 mM NaCl. However, the combination ofsalinity (250 mM NaCl) and waterlogging increasedpuccinellia shoot DM by 150% but decreased shootDM of tall wheatgrass by 90% (compared with salinityalone). Under saline/waterlogged conditions, puccinelliashowed better exclusion of Na+ and maintenance ofK+/Na+ in the shoots than tall wheatgrass. Weconclude that the zonation of puccinellia and tallwheatgrass is associated with differences in their ionregulation which leads to substantial differences intheir growth under saline/waterlogged conditions.