Effects of salinity on water relations and ion uptake in three tropical forage crops

In an hydroponic experiment the effect of different salinity levels, viz., 0, 40, 80 and 120 mol m⁻³, was evaluated on osmotic potential and uptake of various anions and cations by three tropical forage crops, i.e., teosinte (Euchlaena maxicana cv. Local), maize (Zea mays cv. Vijay composite) and sudan grass (Sorghum Sudanese cv. Pioneer ‘Hara Sona’). An increase in the salinity level increased the osmotic potential and contents of Cl⁻, SO₄⁻² PO₄⁻³, and Na⁺ but decreased NO₃⁻, K⁺ and K⁺/Na⁺ ratio. However, the different forage crops showed marked difference in the amounts of ion uptake and their distribution in different plant parts. The values of osmotic potenial, Cl⁻ and PO₄⁻³ present in the different plants parts were of the order of third leaf > young leaf > root whereas SO₄⁻² and NO₃⁻ were present in the order of roots > third leaf > young leaf. Sudan grass, which was more tolerant than maize and teosinte showed lower values of osmotic potential, Cl⁻, SO₄⁻² and Na⁺ but higher PO₄⁻³ and K⁺ as compared to latter two crop the Na⁺ content in the roots of sudan grass was greater than its leaves. Restriction or exclusion of Na⁺ in the roots and higher K⁺/Na⁺ ratio appears to be one of the reasons for more salt tolerance of sudan grass.