The usefulness of a ground-based sensor embedded on tractor for monitoring the growth of winter wheat using a two plant nutrition active sensors (CropSpec) and RTK-GPS was investigated in this study. In order to consider the reliability of the results, the winter wheat was cultivated in farm land of Hokkaido University. Four levels of N fertilizer were applied to make differences in crop conditions, and growth information was acquired at four growth stages. A strong correlation (R² > 0.70) for Nitrogen Sufficiency Index (S1 value) and ground truth data was found in the second stage of data collection. Also, a strong relationship (R² > 0.90) between in-season estimation (INSE) of S1 value and other vegetation indices acquired using a spectroradiometer as a passive sensor demonstrated good performance of CropSpec. However, for diagnosis of crop growth condition for variable rate application, use of the S1 value without elimination of different measurement times is recommended.