Effects of Potassium and Sodium Concentrations on Growth and Cation Accumulation in Pasture Species Grown in Sand Culture

摘要

The effects of potassium (K) and sodium (Na) on growth and cation accumulation in pasture species nwere examined in two sand-culture experiments. In the first experiment perennial ryegrass was subjected nto a wide range of K and Na concentrations, whereas the second experiment examined the effects of npotassium-sodium substitution in solution on nine pasture species. nLarge increases in yield were obtained by increasing K concentrations. However, near maximum nyields were also observed at suboptimal K concentrations when Na was included in the nutrient solution. nHigh yields occurred when the ryegrass tops contained at least 4.8% K (1200 m.e./kg) without Na, but nonly 1.4% K (360 m.e./kg) with Na. nAlthough Na reduced K accumulation in ryegrass, the effect of K on Na accumulation was nconsiderable. All species showed a high K selectivity against Na, with subterranean clover being the least nselective. However, all species were capable of high levels of Na accumulation in the tops. It was found nthat Na uptake was dependent on K concentration and, to a lesser extent, on Na concentration. nCalcium and magnesium uptake was reduced by K and Na, but the reduction by K was greater than nthat of Na at equivalent concentrations. The relevance of these findings is discussed.