Does Salinity Inhibit Alfalfa Leaf Growth by Reducing Tissue Concentration of Essential Mineral Nutrients?

The increased salinity of arid and semi-arid lands has become a problem of great concern in agriculture. The possibility that the inhibition of leaf growth in alfalfa (Medicago sativa) growing under saline conditions may be associated with a reduction in ion concentration in the leaf was investigated. Seeds of alfalfa cv. Buraimi were sown in PVC cylinders filled with loamy sand and arranged in large pots embedded in the soil with the rim just above the soil surface. This arrangement simulated plants grown under field conditions. Seedlings were irrigated with saline (12.2 dS m?1) and nutrient solutions (full strength or 20 times dilution) twice weekly. After 6 weeks the plants were harvested and separated into roots, stem and leaves. The leaves were further separated into lamina and petioles and analysed for the major and minor nutrient elements. Salinization significantly reduced the fresh weights of the roots, stem and leaves as well as the concentration of N, K, Ca and Mg in the leaf tissue. With the exception of Cu concentration, which was enhanced by salinity, all the micronutrients (B, Zn, Mn and Fe) had reduced concentrations in the leaves of salinized alfalfa. The application of an external nutrient solution, especially the full-strength solution, produced an increase in leaf growth and leaf nutrient element concentration. On the basis of these results it was concluded that reduced leaf nutrient concentration may be one of the primary causes of the inhibition of leaf growth that was characteristic of alfalfa growing under salinity stress.