The purpose of this study was to characterize spatial and temporal variations in soil physical properties and toexamine possible differences that might occur when the crop rotation shifted to rice cultivation. Soil samples from0-20 cm and 20-40 cm depth were collected on a 100×100 m grid basis over a 45 ha field, in May 2005 and May2011. The geostatistical methods were used to model the variance structure of gravimetric water content (GWC),soil bulk density (BD), penetration resistance (PR) and aggregate stability (AgS). The coefficient of variations were17.5% for GWC, 7.1% for BD, and 25.0% for PR at surface and 12.8% for GWC, 6.7% for BD, and 17.1% for PRat subsurface. PR at subsurface (>2MPa) and BD at surface and subsurface soils (1.47 g cm-3) exceeded thethreshold values in some fields of the study area. Temporal variations of GWC and PR at 0-20 cm and 20-40 cmdepths were significant (P<0.01) while BD was significantly varied only at 20-40 cm. Spatial correlation ranges ofGWC, BD and PR varied from 72 m to 433 m in 2005 and 40 to 1524 m in 2011. The spatial dependences of GWC,BD and PR at surface were moderate, and AgS had strong dependency at this depth. The spatial distribution mapsof soil physical attributes are useful in identifying the limiting factors and take necessary precaution to preventfurther loss of soil quality.

The purpose of this study was to characterize spatial and temporal variations in soil physical properties and to examine possible differences that might occur when the crop rotation shifted to rice cultivation. Soil samples from 0-20 cm and 20-40 cm depth were collected on a 100×100 m grid basis over a 45 ha field, in May 2005 and May 2011. The geostatistical methods were used to model the variance structure of gravimetric water content (GWC), soil bulk density (BD), penetration resistance (PR) and aggregate stability (AgS). The coefficient of variations were17.5% for GWC, 7.1% for BD, and 25.0% for PR at surface and 12.8% for GWC, 6.7% for BD, and 17.1% for PR at subsurface. PR at subsurface (>2MPa) and BD at surface and subsurface soils (1.47 g cm-3) exceeded the threshold values in some fields of the study area. Temporal variations of GWC and PR at 0-20 cm and 20-40 cm depths were significant (P<0.01) while BD was significantly varied only at 20-40 cm. Spatial correlation ranges of GWC, BD and PR varied from 72 m to 433 m in 2005 and 40 to 1524 m in 2011. The spatial dependences of GWC,BD and PR at surface were moderate, and AgS had strong dependency at this depth. The spatial distribution maps of soil physical attributes are useful in identifying the limiting factors and take necessary precaution to prevent further loss of soil quality.