Shallow Groundwater as Subsurface Irrigation for Rice Cultivation in Sendatani Paddy Field

Abstract

Sedatani paddy field is known to have sufficient water supply even in drought period. Evapo-transpiration of this area was reported varying with the existence of different planting stages. The shallow groundwater level were observed at some points, including wells at the mountain foot and a one meter depth measuring pit that was prepared in the middle of paddy area. Functionality of the shallow groundwater as subsurface irrigation is studied using combination of models of vertical water movement in soil, water uptake by root and evapo-transpiration. The approach is based on the condition of the paddy field, which is only ponded for about two weeks with its current traditional water management. Capillary rise is expected to occur to bring up soil moisture from the water saturated zone near the water table to the root zone, and is approached by using vertical soil water movement equation. The balance between capillary rise, plant water demand and recharge to the water table shows how the shallow groundwater functions as subsurface irrigation in the area.