The Effect of Plucking and Pruning on the Reduction of Radioactive Caesium Concentration in Tea Leaves Grown in Kanagawa Prefecture

Abstract

We conducted this study to understand the regional differences of radioactive caesium concentration(¹³⁴Cs +¹³⁷Cs) in the first crop of tea in Kanagawa prefecture. No relations were observed between the radioactive caesium concentration(¹³⁴Cs +¹³⁷Cs) in the first crop of tea and the sampling point of distance from the Fukushima Daiichi Nuclear Power Plant, altitude, amount of rainfall(March 15 to 31, 2012), and frequency of rainfall(March 15 to 31, 2012).
Multiple regression analysis was performed to understand the reduction factor of ¹³⁷Cs concentration from the second crop of tea. The reduced ¹³⁷Cs concentration was related to the ¹³⁷Cs concentration in the first crop of tea(X₁) and frequency of plucking and pruning(X₂).
Multiple correlation coefficients of the analysis with reduced ¹³⁷Cs concentration as the dependent variable and X₁ and X₂ as explanatory variables was 0.915(p<0.01), coefficients of determination were 0.838. In the case of the analysis with ¹³⁷Cs reduction rate as the dependent variable and X₂ as the explanatory the variable was 0.755(p<0.01), and the coefficients of determination was 0.570.
The regional differences in radioactive caesium concentration did not depend on distance from Fukushima Daiichi Nuclear Power Plant, altitude and precipitation in Kanagawa Prefecture. However, it became clear that the reduction rate of ¹³⁷Cs concentration from the second crop of tea could be explained to be about 57% by frequency of plucking and pruning.