Abstract
The effects of four fertilizer elements (nitrogen, phosphoric acid, potassium, and lime) and compost on rice yield were retrospectively analyzed 77-year archive records since 1926. A causal link between the fertilizer elements and the rice yield was not obvious in multi-regression analysis, probably because some other factors contributed to the yield. In this study, causality analysis was done to clarify the correlation of the yield with fertilizer elements, and some other factors by using graphical modeling (GM) for the effect of the four elements. The causality graph (chain independence graph) obtained by the causality analysis suggested that: (1) application of fertilizer elements resulted in decreased soil fertility with the lapse of time, (2) nitrogen, phosphoric acid, and potassium increased the rice yield directly, and (3) lime increased the yield, not directly but by strengthening the fertilizing effect of other elements.
