Accumulation of mineral nitrogen in the soil is the result of interactions between weather, soil conditions and soil organic matter. Understanding these interactions will contribute to interpreting the results of soil N tests, and should ultimately improve the accuracy of nitrogen fertilizer recommendations based on soil tests. Soil samples were collected from three different landscape positions in 30 Ontario fields on a weekly basis from mid-April to early July on three consecutive years (2001 – 2003). Initial soil mineral N contents in these fields averaged 12.4 mg/kg of NO₃-N, and 3.3 mg/kg of NH₄-N, while the mineral N contents at the final sampling date averaged 23.6 mg/kg of NO₃-N, and 3.8 mg/kg of NH₄-N. Accumulation of soil mineral N at these sites will be discussed in relation to the temperature and moisture conditions.