Studies on manganese deficiency in citrus. II.

Abstract

The investigations on manganese deficiency and its control were carried out from 1955 to 1957 on different kinds of citrus growing in Kanagawa Prefecture.The manganese deficiency symtoms were clear in June when the spring-flush leaves had reached the full size. The interveinal tissues of the leaves turned yellow, leaving a band of green tissues on both sides of the main veins and the mid rib. The contrast in the color of the main veins and adjacent tissues with the interveinal chlorotic portion was not so clear as in zinc deficient leaves. Such leaves were observed throughout the tree, irrespective of the directions in which the orchards were sloping.The severity of manganese deficiency seems to vary from variety to variety, i.e., Naruto (C. medioglobosa Hort.) and Natsudaidai (C. natsudaidai HAYATA) showed the severest symptoms, Unshiu (C. unshiu MARCOV.) showed them moderately, while early Unshiu and sweet oranges were slightly affected.Manganese content in spring-flush leaves increased till August, and thereafter remained fairly constant. Leaf analyses were done in order to find out the manganese content of leaves in 150 Unshiu orchards located in Kanagawa Prefecture. Close relationship between the severity of deficiency symptoms and the manganese content of leaves was recorded. All orchards with leaf manganese less than 15ppm on dry weight basis showed the deficiency symptoms, and 77 per cent of the orchards with leaf manganese less than 20ppm also showed these symptoms.Manganese content in citrus leaves of Kanagawa Prefecture were comparatively lower than those of the other districts, i.e., 71 per cent or more of the orchards in this Prefecture had manganese content lower than 25ppm on dry wight basis. Manganese deficiency symptoms were found in 67 per cent orchards on volcanic ash soils, where average leaf manganese content was 16.01ppm; in 27.3 per cent of the orchards on volcanic gravelly sandy soils the average leaf manganese content was 20.91ppm; and in 36.8 per cent of the orchards on gravelly clay soils it was 21.5ppm.Contents of different elements in leaves collected from 100 orchards in 1956 ranged as follows; nitrogen, 2.88-4.14 per cent; phosphorus, 0.14-0.24 per cent; potassium, 0.762-44 per cent; iron, 95-375ppm. A positive correlation was noted between manganese and phosphorus contents in the leaves and it was statistically significant at 1 per cent level.To contral manganese deficiency, one or two sprayings of 0.4 per cent solution of manganese sulfate before the leaves of spring-flush reached the full size were found effective. Mixture of lime and the above solution appears to be less effective in controlling the manganese deficiency.The soil applications of manganese fertilizers showed no favourable effect on the plants. Foliar applications of manganese to the deficient trees increased manganese content in young spring flush leaves sampled a year after spraying as compared with leaves of the same age from unsprayed trees.