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Wheat maturity is an important factor for appropriate harvest timing and quality. The relationship between large-scale soil distribution obtained from satellite images (Niwa et al., 2004) and progress of wheat harvest for the years 2002 and 2003 in Memuro, a town in the Tokachi district of Japan, was examined.

The results are summarized as follows:

1) The progress of wheat harvesting was non-uniform on middle and high terraces, which are the predominant geographical sections in the Tokachi district. Wheat harvest was delayed in high-elevation areas and areas of poorly drained soil.
2) For wheat at about same altitude, the protein content of wheat grain tended to increase in proportion to the delay in wheat maturation. Therefore, the delay of wheat harvest in poorly drained soil was regarded as resulting from nitrogen oversupply in the wheat root zone.
3) The subsoil of poorly drained soil had unfavorable physical properties, and wheat root system development was restricted.

4) Field survey in 2002 found elevation and subsoil physical properties to account for 70% of the non-uniformity in wheat maturity. Accordingly, toward achieving appropriate wheat maturation, it is necessary to conduct soil improvement by subsoil improvement as well as to reduce nitrogen application in poorly drained soil based on large-scale soil map.