Negative pressure difference irrigation (NPDI) is considered to be an attractive mode of irrigation because water use efficiency in this case is higher than that in conventional irrigation methods such as basin irrigation, furrow irrigation and sprinkler irrigation. In order to investigate the water balance in a NPDI system, experiments involving the use of a soil column, porous pipe and water reservoir were carried out in a temperature and humidity controlled room. The evaporation (M_eva), supplied water (M_sup), soil water storage (M_soil), wetted soil surface area and configuration of the wetted soil around the porous pipe were determined for three different negative pressures. Empirical equations were proposed for the calculation of M_eva and M_soil.
The proposed simple model could well reproduce the temporal variations in M_eva and M_soil. With a decrease in the negative pressure, the water use efficiency increased and was in the range of 0.92 to 0.97.