The relationship between exchangeable soil magnesium and response by sugar beet to magnesium sulphate

Abstract

SUMMARYFifty-three experiments made between 1959 and 1968 tested the response to magnesium sulphate by sugar beet on fields where magnesium deficiency symptoms were expected. Soil samples, taken before applying fertilizers, were analysed for exchangeable magnesium by four methods. Sodium, potassium and calcium in the soil extracts were also measured to determine whether they influenced response to magnesium.Results of different methods of analysing soil for magnesium were related to each other and to the percentage yield-response to magnesium fertilizer. The concentration of other soil cations did not affect response to magnesium fertilizer, but giving other cations, especially sodium, as fertilizer decreased the concentration of magnesium in the crop. Nevertheless, even on fields deficient in magnesium, the largest yield was from plots given sodium and posassium fertilizer together with a dressing of magnesium.Sugar beet grown on soils containing less than 20 p.p.m. Mg extracted with ammonium nitrate usually gave a profitable response to magnesium fertilizer. When soil magnesium was 20–35 p.p.m., yield of sugar beet on some fields was increased slightly. Plants in some experiments had poorly developed root systems and response to magnesium was then always larger than expected from soil analysis.