Abstract
This study was carried out on the manganese deficiency of Citrus unshiu in relation to soil and tree conditions, growing on volcanic soils in Kanagawa Pref.
Both soil and leaf samples were obtained from 7 orchards located on gravelly clay loam and 34 orchards on volcanic silty clay loam in September of 1956. Field surveys of root distributions were made in September of 1957, in 8 orchards located on volcanic gravelly loam and 16 orchards on volcanic silty clay loam, when both soil and leaf samples were obtained in each orchard. In March of 1963, the fresh weight of feeder roots in a given volume of soil beneath of four trees, two manganese deficient trees and two normal trees, were compared.
Hot-HCl soluble manganese content of this area was remarkably lower than those of the other areas in Japan.
Manganese deficiency symptoms in leaves were not found in the trees growing on the soils which contained more than 10ppm of exchangeable Mn, more than 150ppm of easily reducible Mn, and more than 50ppm of 3N ammonium dihydrogen phosphate soluble Mn. But both of manganese deficient trees and normal trees were found in the orchard soils which contained less than these critical levels. About 90 per cent of orchards in this survey (50 orchards during 1956 to 1957), however, contained less than above values of each manganese fraction in their soils. These critical values are higher than those obtained with oat or upland rice plants.
Soil reactions were relatively acidic in all soils. Soil pH was a little higher in manganese deficient orchards than normal orchards. However, the differences of soil reactions between manganese deficient soils and normal soils varied in significancy year by year.
There was a difference between manganese deficient trees and normal trees in the developmental patterns of feeder roots in the surface 0 to 20cm depth of soil. The fresh weight of feeder roots in a given volume of soil was less in the former than the latter. This difference may be due to the soil management system and to the fruiting of trees.
Basing on the above results, the mechanism of development of manganese deficiency in citrus trees is discussed.
