Studies on the RIKUDEN (The paddy field converted from upland field) : (1) Increase in yield of rice on the RIKUDEN : (2) Analysis of high productivity of the RIKUDEN

Abstract

1. Higher productivity of RIKUDEN than the ordinal paddy field was recognized by the field experiments. In spite of the poor initial growth, rice plants cultivated on the RIKUDEN showed better growth in later stages and produced high yield. The high yield on the RIKUDEN can be accounted for by the following characteristics of the RIKUDEN; high percolation of water through RIKUDEN soil, slight differentiation of plow sole layer, less degradation of soil, higher Eh value of soil during the growing period, high humification degree though three essential elements and humus content were lower, and larger soil volume-weight. On the RIKUDEN the roots of rice plants stretched healthy to deep layer and kept high activity even at the latter growth stage. Moreover, many alive leaves are observed after heading with plants on the RIKUDEN. Suffering from diseases and retardation of growth at latter stage are both few, and the straws were stronger. 2. In pot experiments, where the above mentioned characteristics of the RIKUDEN soil such as the high percolation of water, conditions of subsoil, more supply of nutrients by irrigation water, and larger soil volume-weight were eliminated, the same tendency of growth and yield of rice plants as that of field experiments was obtained. So that the high productivity of the RIKUDEN must be attributable for the genuine property of the surface soil of RIKUDEN, in addition to the above mentioned characteristics of the RIKUDEN field. Application of Bentonite was effective not only in preventing excessive percolation of water but also in increasing the absorption of nutrients such as SiO2, CaO, MgO, and MnO by plants, and resulted in the yield-increase with both kinds of soil.