On the small islands of Okinawa, reliance on groundwater is high. The main land use in areas of groundwater recharge is sugarcane fields. To model groundwater recharge in these fields, it is important to analyze infiltration, so the appropriate choice of soil hydraulic parameters is important. Sugarcane crops can take up to 2 years to mature, so the effects of time on soil physical parameters and groundwater recharge need to be considered. To model groundwater recharge, we collected 49 soil core samples 4 times in 2½ years in 7 fields and measured soil physical parameters. Using cluster analysis, we classified the data and groundwater recharge, which was simulated in Hydrus-1D software. Values of bulk density, saturated hydraulic conductivity, and soil hydraulic parameter n were related to time after planting. Cluster analysis identified 4 clusters according to groundwater recharge rate and soil physical condition, and the results were affected by the time of sampling. These results indicate that it is necessary to take sampling date into account while simulating groundwater recharge in sugarcane fields.
