This study proposes a theoretical model to predict soil wetting pattern and water balance in a negative pressure difference irrigation (NPDI) system and describes laboratory experimental results from which this model was derived. The experiments were conducted by using a porous pipe, a water reservoir and a soil column filled with Kawanishi sand. The temporal variations in volumetric water content profile, supplied water, soil water storage and evaporation were calculated by the proposed model.

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... The calculated results were in good agreement with the experimental results. The margin of error of the water balance was in the range of 3 to 7 %. It is concluded that the proposed model is valid for an optimal design of the NPDI system.