Effects of sodium fertiliser on the chemical composition of perennial ryegrass and white clover leaves of different physiological ages

A field experiment was conducted to examine the effects of applying sodium fertiliser on the chemical composition of perennial ryegrass and white clover leaves of different physiological ages. When no sodium fertiliser was applied the cation concentrations increased up to the point of senescence in grass leaves and then declined in the dead leaves. Sodium fertiliser increased the contents of sodium from 6 to 9 g kg -1 DM and magnesium from 2.2 to 3.4 g -1 kg DM in young grass leaves, but both declined to a low level in dead leaves. It decreased the content of potassium in young grass leaves and calcium in older leaves. Clover leaves were less responsive to sodium fertiliser than grass, but older clover leaves had an increased sodium content and reduced calcium content when sodium was applied. All clover leaves responded to sodium by increasing chloride and reducing magnesium contents. The nutritional value of grass, but not clover, was reduced by sodium fertiliser, with an increase in fibre content and a decrease in crude protein content and DM digestibility. This probably occurred because of the high content of sodium in the herbage without sodium fertiliser. It is concluded that young grass leaves tend to be more responsive to sodium fertiliser than old leaves, and that clover is less responsive than grass.