To grow fruit plants, farmers in the Vietnamese Mekong Delta (VMD) must use
raised bed constructions to avoid waterlogging during the rainy season. This study
aimed to evaluate the effects of the age of the raised beds on the soil physicochemical
properties of longan orchards located in the VMD. Two raised bed systems were
evaluated: a young bed constructed 10 years ago and an old bed constructed 42 years
ago. Soil samples were collected from five different soil layers (0–20, 20–40, 40–60,
60–80, and 80–100 cm) with four replicates per layer. Soil samples were tested for
pH, electrical conductivity (EC), available phosphorus (AP), total nitrogen (TN), soil
organic matter (SOM), exchangeable cations (Ca2+, K+, Mg2+, and Na+), cation
exchange capacity (CEC), bulk density (BD), soil porosity, available water-holding
capacity (AWC), particle composition (sand, silt, and clay), and size. The soil pH was
approximately 1.0 units lower in the old bed compared to the young bed at depths of
0–20 and 20–40 cm. The BD was higher in the old bed (0.15 g cm-3) than in the
young bed at a soil depth of 0.4 m. SOM, AP, exchangeable cations (Ca2+, Na+, and
Mg2+), AWC, and soil porosity were significantly lower in both the topsoil (0–20 cm)
and subsoil (20–40 cm) layers in the old bed than in the young bed. In particular, the
SOM, AP, AWC, and soil porosity contents in the old bed decreased by 18%, 20%,
15%, and 17%, respectively, compared with those in the young bed at soil depths of
0–40 cm. Therefore, cultivating raised bed soil for a longer period significantly
reduced the soil exchangeable cations, porosity, and fertility of the surface and
subsurface soils. Based on these results, farmers should use soil conservation
practices, such as cover crops, rice straw mulching, and soil amendments in their
orchards to mitigate topsoil degradation.