Formation and Expansion of Salt Patches in the Paddy Field I. A Salinization Process Observed in the Field

Abstract

Salt patches (salty and barren patches) which recognized inside paddy fields of Northeast Thailand were examined in the fields. Repeated and detailed observations revealed that one type of salt patches were covered with sandy materials and was associated with destructed borders. These salt patches were formed and expanded both by spreading of the salty materials from borders of the paddy fields and by intrusion of the salty materials from the moderately to strongly salt-affected places by erosion which crossed the destructed parts of borders of the paddy fields. This process quickly occurred mainly at the prerain period to the beginning of wet season when a large amount of salt was accumulated on the surface of soils at moderately to strongly salt affected places and intermittent heavy rain induced rushing runoff water. In other words, this type of salinization is consisted of two steps. The first step is accumulation of salt at the soil surface in rather limited places and the second step is wide spread of the salty materials formed but the first step. This process is hypothesized to be applicable to most of the salinization in Northeast Thailand. Another type of salt patch was not associated with the destructed borders and mainly found inside a few fields on the slope. It may be formed by coming up of the salt from below in the dry season which was leached down to the depth of the neighboring paddy field in the rainy season. Necessity to understand type and steps of salinization before countermeasures against salinization were proposed and emphasized.