The purpose of this experiment was to investigate the growth of mint in successive cropping and to find suitable methods of manuring, especially in reference to the soil of granite origin. (1) In ordinary successive cropping, the branch and stalk of mint plants declined in number and the yield of oil accordingly decreased, the tendency being more remarkable by the soil of granite origin. (2) The more acidified the soil in successive cropping, the less yield in oil resulted in the succeeding years compared with that in the first year. The absolute amount of oil yield became richer when the soil was applied with some complementary elements of fertilizer. (3) When it was cultivated yearly under linle-deficient condition, the mint yielded less oil; the soil being acidified and alkali earth metals, alkali metals and other necessary elements being lost steadily with the increase of unfavourable elements such as Al, accumulating in turn. In the case of ammonium sulphate deficiency the oil yied became richer year by year, although less in the absolute amount of production, and the soil remained nearly neutral and every beneficial constituent was richer, and injurious constituents were less remarkable in the soils tested. (4) For successively cropped soil, the cauterized phosphatic fertilizer was much favourable compared with the superphosphate of lime, and rape-seed-oil-cake was found best for yielding of oil; the latter showed, however, a lack of Mn, FeIII, Ca, and K, each being considered necessary to the growth of mint.
