Pattern of occurrence of surface soil separation in paddy fields

To analyse the occurrence of surface soil separation (S. S. S.) in paddy fields, we studied the external appearance of the S. S. S. layer and the changes in the population of associated algal species in the layer. Furthermore, we studied the role of diatoms (Bacillariophyceae) during the initial stage of layer formation. The formation of the S. S. S. layer in paddy fields exhibited the following sequence. Firstly, the fine soil particles that accumulated on the soil surface after puddling aggregated rapidly due to the activity of diatoms, leading to the formation of a thin, light brown layer. Secondly, the diatom population continued to increase resulting in further aggregation of soil particles. Furthermore, on this stage, the increase in the photosynthetic activity of algae resulted in the accumulation of oxygen which subsequently led to the floating of the layer. Thirdly, filamentous blue-green algae (Cyanophyceae) i. e. Osillatoria sp. started to grow and then become dominant, conferring a green color to the layer. Finally, due to the large population of blue-green algae soil particles, become more tightly bound resulting in the strengthening of the layer.