In the Mekong Delta (MD), fruit trees are usually grown on raised-beds to avoid submergence due to annual flooding. The soils are mostly alluvial and disarranged from the natural soils. The soil may be adversely impacted temporally, particularly with its physical properties. The study was conducted on 10 citrus plantations in Hau Giang province, MD, to illustrate if the covariance between clay content and age can be separated from the impact of soil ageing on compaction; we further discuss the design of how to make an investigation where only age is the analyzed event that age has a covariance with the spatial scale. Soil sampling was done in the dry season 2010 at two soil depths for each raised-bed to analyze soil physical properties. Soil texture can be classified as silty-clay soil. The bulk density of topsoils ranged from 0.76 to 1.18 g cm-3 and slightly lower than subsoils; 0.85 to 1.24 g cm-3. Saturated hydraulic conductivity spanned the range from 2.04 to 5.43 m day-1 for topsoils and significantly higher than in subsoils; 1.4 to 5.5 m day-1. Organic matter was in the range of 4.4 to 12.2% for topsoils and significantly higher than in subsoils; 3.0 to 9.6%. A significant tendency of soil degradation with aging was found. Clay content showed a covariance with age of raised-beds counteracting the compaction processes. The high clay content for the aged raised-bed may have been hiding some of the compaction process. The relation between age and soil degradation was seen for the larger pore sizes within the water retention curve.
Key words: Soil physical properties, soil texture, soil compaction, Mekong delta.
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