The effect of replacing potassium by sodium on cation uptake and transport to the shoots in four legumes and Italian ryegrass

SUMMARY White clover, red clover, lucerne, sainfoin and Italian ryegrass were grown in a series of culture solutions in which 0, 25, 50, 75 and 100% of the potassium was replaced by sodium. In the shoots, the potassium: sodium ratios indicated selectivity for potassium which decreased in the order: sainfoin>lucerne>red clover>white clover > Italian ryegrass. In the roots only sainfoin showed selectivity for potassium: with the other species the ratio of potassium to sodium in the roots was similar to that in the other species the ratio of potassium to sodium in the roots was similar to that in the culture solution. All species showed selective transport of potassium to the shoots in preference to sodium: this was least in Italian ryegrass and white clover and greatest in sainfoin, which in contrast to other species also showed restricted transport of potassium to the shoots. Replacement of potassium by sodium slightly increased the magnesium concentration in the shoots but had no effect on the calcium concentration.