Numerical analysis of anaerobically digested slurry with irrigation water in rice paddy

The objective of this study was to analyze the two-dimensional spatial and temporal distribution of anaerobically digested slurry in rice paddy fields. For this investigation, MIKE 21 HD (MI) was used, and advection and diffusion were taken into consideration. To verify the model for rice paddy fields, a field observation was conducted at a lysimeter, where anaerobically digested slurry was mixed with irrigation water and the fluctuations of T-N at five points were measured. Though some factors, such as undulations on the soil surface, created discrepancies between anticipated and actual values, the overall calculations agreed with the measurements, indicating that the model was fairly adaptable. To estimate the uniformity of distribution of anaerobically digested slurry, the spatial and temporal distribution of T-N at the lysimeter was simulated with MI. The results indicated that T-N was not distributed evenly with low level T-N around the water inlet. To determine a method that would effectively distribute anaerobically digested slurry, a scenario with a trench and two inlets was simulated. Trenches 3.00x10^-2m deep and 6.17x10^-2m wide were installed longitudinally among the rice plants. In addition, both lateral and longitudinal inlets were introduced. The water from the inlet in the ar-direction was faster than that in the In this scenario, the blocks on the levee were removed, and T-N from both inlets was fixed in the entire simulation period. Also, T-N level was fixed the entire time, assuming that anaerobically digested slurry was continuously mixed with the irrigation water. The results revealed uniform distribution of anaerobically digested slurry in terms of T-N in 50 minutes, indicating that those introductions effectively distributed anaerobically digested slurry in a rice paddy.