LEAF, STOLON AND ROOT-GROWTH OF WHITE CLOVER (TRIFOLIUM-REPENS L) IN RESPONSE TO IRRIGATION WITH SALINE WATER

The effect of irrigation with water at salinity concentrations of 2.6 and 5.2 dS m-1 on the growth of pure swards of six cultivars of white clover (Trifolium repens L.) was examined over three irrigation seasons at Tatura, Victoria, Australia. After two irrigation seasons, soil EC(e) levels increased to 6 dS m-1 at 0-60 cm depth in the higher salinity treatment resulting in highly significant (p<0.001) reductions in shoot dry matter production, flowering densities and petiole and stolon densities. These saline conditions also increased (p<0.001) concentrations of Cl and Na in the shoots and reduced (p<0.001) leaf water potentials and canopy photosynthetic efficiency rates especially at high temperatures. In contrast, root growth increased at shallow depths (0-15 cm) under both saline irrigation treatments (p<0.001). Cultivars differed significantly in salt tolerance (p<0.001), with cultivars Haifa and Irrigation exhibiting superior tolerance in terms of lower reductions in herbage yield (p<0.05) and petiole densities (p<0.001) during one irrigation season and lower concentrations of Na and Cl in the shoots (p<0.05) compared with the other four cultivars (Aran, Kopu, Pitau and Tamar). In addition, canopy photosynthetic efficiency rates (A*) in plots irrigated with water at 5.2 dS m-1 were higher in cultivar Haifa compared with cultivar Tamar (p<0.05). The salt tolerance ranking obtained for the six cultivars was in broad agreement with earlier greenhouse studies. Consequently, it appears that, while white clover is an extremely salt-sensitive species, it is possible to grow cultivars which display greater salt tolerance than other cultivars and which provide some scope to increase, or at least to maintain, pasture yields in areas where the soil salinity is low to moderate or where pumped saline groundwater is re-used for irrigation.