**4. Conclusions**

In paddy-upland rotation fields including soybean cultivation, the field N budget in both upland soybean and paddy rice is negative, and soil N fertility is likely to decrease due to repeated rotation. Application of organic matter is an effective measure to improve the N budget in paddy-upland rotation fields to maintain soil N fertility and crop productivity. The effect of organic matter application on the N budget depends on the type of organic matter. Further evaluation of organic matter management practices and their impact on the N budget is needed.
