Correlation between Percolation Pattern and Soil Horizon Differentiation in a Stratified Soil Column Model of Paddy Field with a Kuroboku Surface

Studies on the influence of percolation pattern in seepage water on several phenomena in a layer (II)

Abstract

The purpose of this paper is to clarify the correlation between the percolation pattern and soil horizon differentiation to oxidized and reduced layers. The model had three layers of the plow layer (Kuroboku soil) of paddy field that is managed yearly by using feritilizer. The stratified soil model column was composed of the Kuroboku soil. The model layers were composed of plow layer (puddling state), plowsole and subsoil (compacted).
In the experiment, DO, pressure head in seepage water, air entry value and Eh were measured at short intervals in the vertical plane, and then, the drainage level was controlled by the soil column. Velocity of the model was about 50 mm/d and that of the other model was about 100 mm/d.
As a result of this observation, the following information was obtained.
1) In the case of a low drainage level (about 90 cm), plow layer and plowsole became a closed system percolation, low DO (1 ppm level), and reduced layers. Subsoil became an open system percolation and high DO (7 ppm level), and oxidized layer.
2) In the case of high drainage level (about 25 cm) in the same column, all layers became a closed system percolation, soon reverting to a low DO, but later becoming reduced layers after about 20 days.
Judging from the above, it is clear that the open system percolation produced an oxidized layer though microbe activation was maximum. The closed system percolation produced a reduced layer at almost a quater of the time required in the inorganic stratified soil column model reported in the previous paper. Therefore, the open system percolation was seen as a necessary and sufficient condition for formation of an oxidized layer. The closed percolation was necessary for a reduced layer. However, it was not a sufficient, and promotion power of reduction is necessary for closed percolation to be a sufficient. The development of reduced layers depends on strength of the promotion power.