Impact of Different Crops on Soil Moisture Characteristics in Rain Shadow Area, Kanchanaburi Province

Abstract

A study on impact of different crop practices on soil moisture characteristics in rain shadow area, Kanchanaburi province using TDR (Time Domain Reflectometry) for monitoring moisture content at various depths was carried out in seven areas, comprising 1, 3-month old cassavas, 6-month old sugarcane, 8-year old neem plantation on moderately fine-textured soil and degraded forest, 8-year old eucalyptus plantation and 1-year old cassava on medium-textured soil. The study aimed at investigating soil moisture changes in relation to soil characteristics and as affected by different crop practices. Moderately fine-textured soil (Typic Calciustert) derived from local alluvium over residuum of limestone and the medium-textured soil (Ultic Paleustalf) formed from local alluvium of quartzite. Result showed that moderately fine-textured soil contained total water content of 38.40-51.17% by volume, which was higher than that of medium-textured soil (29.26-48.53% by volume). The former had 6.74-10.96% volumetric available water capacity (AWC) with most of water filling in micropores whilst the latter containing 7.07-10.01% by volume of AWC due to its having rather good distribution of pore size. Changes of soil moisture content in soils monitored from September 2008-March 2009 revealed that the content increased with increasing depth. Sugarcane held the greatest amount of soil moisture at almost all depths measured. Moisture contents at 0-30 cm depths in both soils were lower than the amount held at permanent wilting point, approximately 2-3 weeks after the last rain. Cassava characteristically had no efficiency in conserving soil moisture, resulting in moisture in the upper part of the soils being lost quite rapidly by evaporation. This plants normally consumed water from the depths between 30 and 40 cm. Fast growing trees such as neem and eucalyptus used gigantic amount of water in soils at the depth of 60 cm downward of which moisture content in capillary fringe zone was reduced as a result. Soil moisture conservation measure for both soils in rain shadow area should consider the use of soil mulching or leaving crop residues on the ground surface in order to reduce the loss of soil moisture by evaporation, especially during drought period.