Sodium (Na) Stimulates Barley Growth in Potassium (K)-Deficient Soils by Improved K Uptake at Low Na Supply or by Substitution of K at Moderate Na Supply

Sodium (Na) can alleviate potassium (K) limitations by either increasing K uptake or by substitution of K functions in plants, but there is limited information about the levels of soil Na and K at which these separate Na effects operate in cereals. Barley was grown in two sandy soils to assess plant growth and nutrient uptake responses with varying soil Na (5-95 mg kg(-1)) and K (30, 90 mg kg(-1)) treatments. Compared with very low Na (5 mg kg(-1)), low Na (35, 65 mg kg(-1)) enhanced barley tillering in low K soil (30 mg kg(-1)) up to 6 weeks after sowing (WAS). Low K with 95 mg Na kg(-1) or adequate K (90 mg kg(-1)) with 65 mg Na kg(-1) also produced more tillers at 6-7 WAS. Shoot dry weight of low K plants was significantly improved by low Na at 7 and 9 WAS and even by 95 mg Na kg(-1) at 9 WAS. While low Na increased shoot K concentration and the K/Na ratio in low K plants, 95 mg Na kg(-1) mainly increased shoot Na concentration at 7 and 9 WAS. By comparison, soil Na had less effect on shoot K concentration and dry weight of adequate K plants. Barley growth at low soil K was stimulated by increasing K uptake at low Na (35-65 mg Na kg(-1)), but mainly by Na substitution of K at 95 mg Na kg(-1), i.e. the beneficial effect of Na on response of low K plants was attributed to two distinct mechanisms that operated at different soil Na levels.

Automated summary

Low concentrations of sodium can enhance tillering of barley in low potassium soil, while high levels of sodium mainly improve growth by substituting potassium in barley plants grown in low potassium soil.