Response by sugar beet to soil dressings and foliar sprays of manganese

Response by sugar beet to manganese in 16 field experiments on organic soils is reported. Soil applications of manganous oxide and manganese silicate “frit” were compared with foliar sprays of manganese sulphate equivalent to 9 and 18 kg/ha Mn in seven experiments (1969 to 1971); three experiments during the same period tested up to three sprays of manganese sulphate, each equivalent to 9 kg/ha Mn on severely manganese‐deficient crops. Six previous experiments (1936 to 1941) compared soil applications of manganese sulphate, in the seedbed and as top‐dressings, with foliar sprays of manganese sulphate in amounts up to 42 kg/ha Mn to the soil and up to 1.5 kg/ha Mn in the sprays. The manganous oxide and the silicate frit did not prevent deficiency and increased neither the concentration of manganese in the leaves during the growing season nor the sugar yield at harvest. Manganese sulphate sprays increased the concentration of manganese in the leaves, cured most of the symptoms and increased sugar yield by up to 1.5 tons/ha. On average of the ten experiments 1969 to 1971, the crop responded little to treatment when less than 20% of plants showed symptoms. When 21 to 60% of plants were affected, the sprays increased sugar yield by 5% and by 17% when more than 60% were affected. Of several extractants tested, the fraction of soil manganese extracted by normal ammonium acetate buffered to pH 7.0 and containing hydroquinone was best correlated with the concentration of manganese in the leaves. The early experiments showed that large soil dressings of manganese sulphate controlled symptoms and increased sugar yield but sprays applying much smaller quantities were equally effective.