SOIL ORGANIC MATTER AND NITROGEN CONTENTS OF SAGA POLDER RICE FIELDS : CHANGES WITH DEPTH AND TIME

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概要

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• Thirteen rice soil profiles developed at intervals from 0 to some 700 years on the soil derived from shallow sea sediments along the Ariake Bay were examined to discover what changes in organic C, total N, and related constituents occurred with time. On an organic C and total N basis, organic matter content of the surface soils, with the exception of the early years of rice cultivation, had a general tendency to increase as a linear function of logarithm of time. By contrast, the organic matter content in the subsoil B horizons decreased significantly. Thus, the organic matter profiles indicated the development of A and B horizons, causing distinct horizontal gradients with time. Using total N content, C/N ratio varied from 16.08 to 7.81 with the lowest values found in the B horizons as time elapsed. Inorganic N was present mainly as fixed NH_4^+-N accounting for 5 to 31% of the total N, whereas exchangeable NH_4^+-N was the dominant extractable inorganic N. Fixed NH_4^+-N occurred in overall equal abundance in all horizons of the sampled profiles as compared with organic C or total N, suggesting that most of it was indigenous. Accounting for the inorganic N fraction, especially the fixed NH_4^+-N, had a marked effect to increase the C/N ratio in the subsoil horizons almost close to that obtained in the surface soils. A close relationship was found between the amount of NH_4^+-N produced by incubation of soil under water-logged conditions and the amount of organic N present in the soil. With the use of this relationship, a correlative means of estimating the content of undecomposable organic N compounds sorbed by clay minerals was presented. A considerable amount of organic N, i.e. 0.045% (450 ppm), was found to be most likely held within the lattice structure of clay minerals, thereby revealing a missing link in the N cycle.

• 社団法人日本土壌肥料学会の論文

著者

• KOGA Hiroshi

  Division of Soils and Plant Nutrition, Kyushu National Agricultural Experiment Station, Ministry of

• Gotoh Shigeyoshi

  Division Of Soils And Plant Nutrition Kyushu Agricultural Experiment Station Ministry Ofagriculture

• Koga Hiroshi

  Division Of Soils And Plant Nutrition Kyushu Agricultural Experiment Station Ministry Ofagriculture

関連論文

• EFFECT OF LONG-TERM APPLICATION OF ORGANIC RESIDUES ON THE DISTRIBUTION OF ORGANIC MATTER AND NITROGEN IN SOME RICE SOIL PROFILES
• BACKGROUND LEVEL OF NITROUS OXIDE IN THE ATMOSPHERE IN RELATION TO FLUX FROM SOIL
• SOIL ORGANIC MATTER AND NITROGEN CONTENTS OF SAGA POLDER RICE FIELDS : CHANGES WITH DEPTH AND TIME

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