Abstracts of Nippon Dojo-Hiryogaku Zasshi 93 - 4

All farmers must understand quantitative productivity and the factors that are important to their farm fields for optimum crop management. This study attempted to esti-mate the soil quality index (SQI) of 61 winter wheat fields in Tokachi District, Hokkaido, over three years. It also examined the relationship between SQI and yield. SQI was estimated as a sum of weighted scores calculated from the value of each soil parameter (surface soil proper-ties), which were adopted as soil diagnostic criteria by the Hokkaido government. A lower score was given when the parameter values deviated from the criteria. The principal component analysis parameters selected for SQI estimation were exchangeable calcium, solid ratio, exchangeable potassium, macropore, and hot-water extractable boron in descending order of spatial variation. Among them, exchangeable calcium and macropore had the greatest impact on low SQI. A significant positive correlation was detected between SQI and yield in 2018, when productivity was low due to heavy rain in May and July, especially in Brown Lowland soils and Andosols with alluvial subsoil. In contrast, a weaker correlation between SQI and yield was detected in Andosols with a thick effective soil layer. This implies that soil should be sampled on an effective soil layer to calculate the SQI. Additionally, in a case where the field contains much gravel in the surface layer, gravel content should be considered because of yield overestima-tion by SQI. Conclusively, this study implied that yield decreased as SQI decreased in a low yield environment with heavy rain only if the field has a thin effective soil layer and less gravel on the surface layer. However, soil quality improvement might stabilize the annual yield var-iation. Moreover, the consideration of meteorological and crop managemental conditions is required to better understand the relationship between SQI and productivity.