Sodium and potassium relationships in sugar beet

Abstract

SUMMARYThree field experiments with sugar beet grown on a light calcareous soil tested a wide range of amounts of sodium and potassium fertilizer with either magnesium or nitrogen. Both sodium and potassium increased sugar yield and there was a large negative interaction between them. Magnesium also increased sugar yield, but the larger dressing of nitrogen decreased it. Sodium, potassium and nitrogen fertilizers also affected the concentration of impurities in the root juice at harvest.Plant samples were also analysed in August when the crop usually contains most sodium. Sodium fertilizer greatly increased the sodium and decreased the potassium concentration in the dry matter of the tops but the composition of the roots changed little. Potassium dressings slightly increased potassium in the tops but did not affect the root composition.Exchangeable sodium in the top soil of plots given sodium fertilizer decreased rapidly early in the season, but increased again from August, probably because sodium was taken up rapidly early in the summer and returned later in dead leaves. Soil potassium decreased throughout the season on plots where potassium was applied, but did not change on plots without potassium fertilizer; this is explained by fixation and release from non-exchangeable forms.On this soil there was no reason to regard sodium in its effect on yield, other than as a replacement for potassium, but its behaviour in the soil and effect on the composition of the plant was quite different.