NITROGEN DYNAMICS IN THE UPPERMOST PART OF SUBMERGED PADDY SOILS IN TEMPERATE AND TROPICAL REGIONS : II. Effect of Segregation of Soil Particles by Puddling on the Dynamics of Submerged Sandy Soil

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The segregation of fine particles in the uppermost part of Thai (Surin) and Japanese (Katagiri) sandy paddy soils was studied under field and laboratory conditions. Under laboratory conditions, the soil was puddled under shallow (1 cm) or deep (12 cm) surface water. There was a pronounced segregation of clay and silt in the uppermost part of the Surin soil when the soil was puddled under deep surface water, the extent of which was similar to that under field conditions. Remarkable segregation of these fine particles also occurred in the Katagiri soil when the soil was puddled under deep surface waster, to a much larger extent than under field conditions. This difference in the sorting effect in the Katagiri soil between field and laboratory conditions may be ascribed to a higher rate of water percolation under the former condition, while in the rainfed Surin soil no water percolation took place under field conditions compared with laboratory conditions. Pudding under deep surface water promoted the segregation of organic matter in the uppermost part of the submerged soil, and the extent was much larger in the Katagiri soil than in the Surin soil. This sorting phenomenon enhanced the ammonification process and suppressed the nitrification-denitrification process in the early to the middle stages of incubation in the Surin soil and in the early stage of incubation in the Katagiri soil.
社団法人日本土壌肥料学会の論文