抄録
We developed the new direct sowing method of paddy rice to get better seedling establishment and higher lodging resistance than those by the former method, namely direct sowing on the surface of flooded soil. In the new method, seeds are coated with calcium peroxide, which promotes emergence and seedling establishment, and sown into flooded soil (to the depth of 1 - 2 cm) after puddling and leveling. We named this method "DIPPS" which is short for "(Di)___-rect Sowing of P__-addy Rice into P__-uddled and Leveled S__-oil". In the recent years, cultivation experiments by DIPPS have been carried out. In some cases of the experiments the yields were even higher than those by the conventional transplanting method. But it was also found that the percentage of emergence of seedling establishment was sometimes seriously low. Several researches in this problem showed that soil reduction is one of the factors that restrains emergence, and further research is required from this viewpoint. We investigated the oxidation-reduction state (ORS) of flooded soil in the vicinity of the seed coated with calcium peroxide (coated seed) and the non-coated seed in two ways, one by an oxidation-reduction electrode (Figs. 6 and 7) and the other by oxidation-reduction indicator (methylene blue) added to soil (Figs. 1-5). 1. The vicinity of the coated seed sown into reduced soil immediately formed a locally oxidized spot (Fig. 3). But it was only until germination (3-5 days after sowing) that the soil-oxidizing effect of calcium peroxide lasted. Thereafter, the soil in the spot was more reduced than that outside the spot (Fig. 4). 2. The vicinity of the coated seeds sown into oxidized soil was in oxidized state for 3 days after sowing. Then, after germination, the vicinity of the seeds was, in some cases, more rapidly reduced than the outside of the vicinity (Fig. 1). The reduction in the vicinity of the coated seed was more temperate in oxidized soil than in reduced soil. 3. The soil was reduced more rapidly within the vicinity of the non-coated seed than the outside from the next day after sowing whether it is sown into oxidized or reduced soil (Figs. 2 and 5). But the degree of the reduction was higher in reduced soil. 4. These observations show the difference in ORS between the soil within and outside the vicinity of the seed coated or not coated and also indicate the specificity of ORS in the vicinity of the seed. Thus, in order to elucidate the relationship between soil reduction and emergence or seedling establishment, ORS of the soil in the vicinity of the seed should be noticed. 5. A part of the promotive effect of calcium peroxide on emergence and seedling establishment could be explained as local oxidation of soil, by which the soil in the vicinity of the coated seed was kept in oxidized state which is supposed to be favorable for germination. But it remained unknown exactly how calcium peroxide stimulates elongation of coleoptile which is essential for the promotion of emergence and seedling establishment. We suspected that unstableness in emergence and seedling establishment had much to do with the shortness of soil-oxidizing effect of calcium peroxide.
