Table 1. General description of seven soil profiles.

Sampling point	Latitude	Longitude	Land use type	Description
TS1	14°56′32.59″	101°58′34.10″	Rice fields	0–220 cm: Brown soil; no change in soil horizon observed
TS2	14°52′06.89″	101°57′58.69″	Sugar cane field	0–30 cm: Brown clay; compact and hard soil; massive structure
TS3	14°33′5.03″	104°56′14.76″	Oak field	0–18 cm: Humus layer
				18–50 cm: Reddish-brown subsandy soil
TS4	15°09′0.77″	105°10′56.44″	Rice fields	0–12 cm: Gray-black root layer; a few plant roots and wormholes
				12–47 cm: Fine silt
				47–100 cm: Light yellow fine silt; numerous brown and yellow spots of iron rust
				>100 cm: Iron manganese nodules layer; red black iron nodules
TS5	15°03′55.86″	104°55′7.50″	Wasteland	0–20 cm: Gray-black fine silt; planting layer
				20–40 cm: Grey fine silt; existing a few roots
				40–112 cm: Existing a small number of iron rusty spot and abundant iron and manganese nodules
				112–180 cm: Red weathering crust
				>180 cm: Bed Rock
TS6	14°58′33.11″	104°23′44.07″	Built-up land	0–20 cm: Fine silt; surface layer
				20–105 cm: Fine silt
				105–160 cm: Lime green sludge
				160–205 cm: Iron manganese tuberculosis layer
				205–405 cm: Lime green clay, lacustrine strata
				>405 cm: red siltstone
TS7	15°11′59.35″	104°30′28.23″	Forest	0–50 cm: Fine silt; lots of plant roots