Evaluation of the spatial distribution of digested slurry supplied with irrigation water to an irregularly shaped rice paddy field

The objectives of this study were to evaluate the spatial distribution of methane fermentation digested slurry (i.e., digested slurry) supplied with irrigation water in an irregularly shaped rice paddy field by considering the effects of the wind, evapotranspiration, and infiltration on the surface water and solute movements, and to suggest a method of supplying spatially-uniform digested slurry. A two-dimensional simulation model is introduced to describe the surface water and solute movements in the rice paddy field. To verify the accuracy of the model, a field observation was conducted. The electrical conductivity (EC) and total nitrogen (TN) values for the surface water were measured while the digested slurry with the irrigation water was supplied to the observational field. The EC and TN values showed that the digested slurry accumulated at the vicinity of the inlet and did not reach the outlet region. The trend in the simulated TN values at the inlet and outlet regions was in good agreement with the measurement data, and the accuracy of this model was confirmed. Using this model, an effective method for uniformly supplying digested slurry to irregularly shaped rice paddy fields was considered. The simulation results indicated that this could be achieved by using an additional inlet and by controlling the inflow flux and the TN in each inlet.