Abstract
The fertilizing effects of four major elements (N, P, K, Ca) and compost in the rice fi eld have been recorded since 1926. Using the experimental data obtained during 77 years until 2002, we performed principal component analysis (PCA) to examine how the yield of rice was infl uenced by each fertilizer element in each year. We found two principal components by using PCA. The fi rst component was considered to relate with the yield when both N and P were applied, and the second with the yield when N and/or P (N or P or both) were not applied. We classifi ed the experimental years according to the result of the PCA, and examined the characteristics of fertilizing effects and climatic conditions in each year group. In the groups with high yield and with both N and P application, the effects of K and Ca were low, and compost was effective. In the groups with high yield and without N or P application, sunlit period was long, when the effects of K and Ca application with both N and P were high. In the groups with long sunlit period, the yield in the plots without K or Ca application was lower than that in the plots fertilized with N, P, K and Ca. This may be because absorption of K was suppressed by defi ciency of K or Ca, and photosynthesis under (in) low humidity was greatly suppressed under such conditions. The results suggest that application of K and Ca with both N and P is more effective under the conditions suitable for photosynthesis with long sunlit period.
