Readily soluble manganese of soils and Marsh Spot of peas

Abstract

1. From an examination of thirty-five soil samples collected in Furneaux & Glasscock's survey of pea soils of the Romney Marsh area of Kent it was shown that the Marsh Spot disease of peas is more closely related to soil reaction than to soil series or soil texture. The disease was not found on any acid soil but was present on most of the alkaline soils. 2. Most of the Romney Marsh soils contained appreciable amounts of free oxides of manganese and of salt-soluble manganese. The soils with Marsh Spot contained less salt-soluble manganese than those on which peas were free from the disease, but this relation depended essentially on the contrast between acid and alkaline soils. Within the alkaline group of Romney Marsh soils, however, analyses for salt-soluble manganese did not always distinguish between contrasted soils; three of the five alkaline soils on which peas were free from the defect were low in salt-soluble manganese. 3. A single extraction with normal calcium nitrate proved as effective as Steenbjerg's series of leachings with normal magnesium nitrate in characterizing the soils. Dilute acids dissolved more manganese than salt solutions. Citric acid gave higher results through reducing the oxides of manganese. The acid-soluble manganese was not related to the occurrence of Marsh Spot. 4. Soils on which oats suffered from Grey Speck disease and sugar beet from “Speckled Yellows” contained little or no salt-soluble manganese. Applications of manganese sulphate, which controlled the diseases in the field, appreciably increased the salt-soluble manganese in the soils. 5. Peas grown in pot cultures in manganese-deficient soils and in a sand-bentonite mixture developed Marsh Spot. Addition of manganese sulphate increased the manganese content of the seeds, especially in sand-bentonite, and controlled the disease.