Rice yield, Soil Organic Matter (SOM), and crop Nitrogen (N) uptake on a fine, silt paddy soil were treated with nitrogen+phosphate+potassium (NPK) and NPK+compost (rice straw) and the same set was maintained as control (no treatment), in Milyang, South Korea (36^o36'N, 128^o45'E, elevation of 12m) from 1980 to 2003. The treatments were then simulated by a Water and Nitrogen Management Model (WNMM) and compared with field measurements. For N, P, and K fertilizers, or urea, triple super phosphate and potassium chloride were applied to the experimental fields at 150kg N per hectare per year, 100kg P per hectare per year, and 100kg P per hectare per year, respectively. Rice straw compost was applied at 10,000kg per hectare per year. The WNMM predictions for 23 years on rice yield, SOM, and N uptake were significantly different under each treatment. The rice yields and N uptake simulated by WNMM depended strongly on solar radiation in weather factor. SOM measured in the field varied as time went on; the reason for such was not clearly observed. R² for the correlation between predicted and measured data for N uptake, rice yield, and SOM were 0.06. 0.12, and 0.04 in control; 0.15, 0.16, and 0.13 in NPK; and 0.41, 0.21, and 0.34 in NPK+compost, respectively. The WNMM predictions of rice yield, N uptake, and SOM in plot treated with NPK+compost showed the highest correlation with measured data. Keywords: simulation, rice, soil organic matter, compost, N uptake