In Hoikkado, the area cultivated with maize (Zea mays L.) has recently increased; therefore, optimal cultivation methods need to be established. For the estimation of appropriate nitrogen (N) fertilizer application rates based on soil N analysis, we grew maize at several N fertilizer rates and in lowland as well as upland soils in central Hokkaido and in andisol soil in Tokachi.

1) A high correlation was obtained between N uptake and grain yield, which differed depending on the type of soil and district.

2) In lowland and upland soils in central Hokkaido, the soil N utilization rate was higher with no N fertilizer treatment than with fertilizer N treatment. In andisol soil in Tokachi, the N utilization rate was lower with no fertilizer N treatment than with fertilizer N treatment.

3) In andisol soil in Tokachi, the higher N absorbed with no fertilizer N treatment ,the lower fertilizer N utilization with fertilizer N treatment.

4) In lowland and upland soils in central Hokkaido, the highest correlation was obtained between N uptake and the sum of hot-water extractable N and inorganic N of soil. The correlation increased as the depth of inorganic N increased. In andisol soil in Tokachi, a high correlation was obtained between N uptake and hot-water extractable N of soil.

5) The estimated N uptake, predicted by total fertilizer N and soil N analysis, was closely related to the measured N uptake (r=0.93–0.94).

We investigated the relationship between nitrogen (N) uptake of maize (Zea mays L.) and total N supplied by the soil and fertilizer at lowland and upland soils in central Hokkaido and in andisol soil in Tokachi. From these results, we estimated appropriate N fertilizer application rates based on soil diagnosis.

1) A significant correlation was obtained between N uptake and total N fertilizer plus hot-water extractable N (soil bulk density was not considered in the present study), except in the case of hot-water extractable N of >70 mg kg⁻¹ in andisol soil in Tokachi.

2) In lowland and upland soils in central Hokkaido, N uptake required for a grain yield of 10,000 kg ha⁻¹ was approximately 210 kg ha⁻¹. In this case, the total fertilizer N plus hot water extractable N (soil depth of 0–10 cm) was 260 kg ha⁻¹, and judging by the amount of mineral N remaining in the soil after harvest, the appropriate amount was 240 kg ha⁻¹.

3) In the case of hot-water extractable N of <70 mg kg⁻¹ in andisol soil in Tokachi, the N uptake required for a grain yield of 10,000 kg ha⁻¹ was approximately 180 kg ha⁻¹. In this case, the total fertilizer N plus hot-water extractable N (soil depth of 0–30 cm) was 320 kg ha⁻¹.

4) Appropriate N fertilizer application rates based on soil N analysis was calculated by subtracting hot-water extractable N from 240 kg ha⁻¹ (lowland and upland soils in central Hokkaido) or 320 kg ha⁻¹ (andisol soil in Tokach).

5) For hot-water extractable of N >70 mg kg⁻¹ in andisol soil in Tokachi, the appropriate total fertilizer N was 140 kg ha⁻¹.

We evaluated the effect of controlled release fertilizer [urea with lime nitrogen (N), coated fertilizer, and nitrification inhibitor containing an N fertilizer] on nitrous oxide (N₂O) emission and yields in a wheat–soybean cropping system in a converted rice paddy field over three years in Shiga Prefecture, Japan. Our results revealed that treatments using the coated fertilizer and urea with lime N reduced the annual N₂O emission factor (including both wheat and soybean cropping periods) by 24％ to 47％ compared to treatments using a quick-acting fertilizer, while wheat and soybean production was stable. In the wheat cultivation period, the use of controlled release fertilizer considerably reduced the peak N₂O emissions immediately after base fertilizer application due to the reduction in inorganic nitrogen during this period. In the soybean cultivation period, there were clear effects of treatment on N₂O emission after base fertilizer application due to large annual variations in N₂O emissions. Further research and development of management approaches are essential to steadily mitigate N₂O emission in converted rice paddy fields.