Physical and Mineralogical Properties of Drained Paddies and of their Reclaimed Counterparts

Abstract

Drained paddy soils were characterized with respect to their physical properties and mineralogy. These properties were related to their observed workability when worked dry. Reclaimed equivalents of the wet paddies were also analyzed to describe changes in the above properties on reclamation. The reclamation period ranges from 2 to 5 years. All reclaimed soils show higher pH than the wet paddy samples. The trend of acidity among the wet paddies is to increase with depth; among the reclaimed decrease with depth. Organic matter is higher in the wet paddies than in the reclaimed. For both soils, organic matter decreases with depth. Where it exists in large amount and well puddled into the soil it causes an intense cementation resulting to poor workability. This is reflected in the aggregate analysis where as much as 69 percent of the initial aggregates resisted the dispersive action of water. Because the soil in a terraced paddy is actually one soil mass broken only by surface cracks, aggregate analysis data can be interpreted to measure the intensity of cementation, hence measure workability. This interpretation is proposed. Moisture constants determined decrease upon reclamation with the greatest decrease exhibited by surface soils. Except for the surface soils, plastic number remained even upon reclamation despite changes in the upper and the lower plastic limits. Where the wet paddy is not tilled during the period of reclamation, subsoils exhibit similar values as the surface soils of the wet paddies. This is observed in Waiahole 1 soils. Clay content in the fine-textured soils ranged from 51 to 67 percent; that of the coarse-textured, as Hanapepe soil has about 42 percent clay as its highest in the profile. This soil is very easy to work when dry. The dominant clay mineral in the paddies is dependent on their location. Where a paddy is located at or near higher lands, the dominant clay mineral tends to be kaolinite. Where its location is a large flat plain, montmorillonite clay tends to be dominant. Examination of thin sections points to the role of plant roots in the establishment of macro-pore spaces in wet paddies. Around these root channels are concentrations of iron oxides. A large area around these root channels are oxide-coated clay particles. These particles show a very faint anisotropy.