抄録
We produced a new core-sampler and an auxiliary soil-cutting implement in order to study more efficiently and exactly the situation of rice root system in paddy fields. And we evaluated the research method statistically in a paddy field of Saga University. The core-sampler and the soil-cutting implement were characterized by smallness, lightness and simplicity. 1. The core-sampler (Fig. 1-1) consists of three parts, that is, an outside cylinder of steel, an inside cylinder of hard vinyl (Fig. 1-3) and a cap of steel (Fig. 1-2). The outside cylinder is 250 mm in length, 93 mm in inner diameter and 4 mm in thickness. The bottom edge of the outside cylinder is sharpened in order to make it easy for the cylinder to penetrate the soil. The inside cylinder, vertically cut into two halves and then connected with tapes, is set in the outside cylinder. 2. When we research the root system in the paddy field, we first drive the core-sampler into the field by striking the cap with a hammer to a depth of 15 cm, which makes it possible to get most of the roots. Second, the soil-cutting implement is inserted into soil along the outer was of the outside cylinder down to the check point, then the handle of the sticker is horizontally turned round to cut of the core-sampler from soil layer (Fig 2). Finally, the core-sampler is pulled up from the field by holding the grips with both hands, then soil cores are taken out of the inside cylinder and washed with running water. 3. Three young rice seedlings (var. Reiho) were planted in each hill spaced 21.5×21.5 cm on 11 June 1981. The rice plants were grown under a standard cultivation system popular in Saga Prefecture. Sampling the roots was carried out at heading time. 4. Sampling posittions of the soil cores are shown in Fig. 4: positon A is just on a hill, B is between two hills and C is the center of four hills. 5. Whole roots of a single hill were sampled by a square monolith sampler sized 21.5×21.5×15.0 cm, the volume of which was equivalent to the roots growing in the sphere of a single hill as shown in Fig. 3. The root amount obtained by the monolith was taken as a standard value in estimating the amount of roots by using the core-sampler (Table 1). 6. If we estimate the whole root weight in an unit area within a limit of 10% error statistically, nine samplings by the square monolith are required. In the case of positions A and B, fifty six and sixty nine samplings are necessary, respectively (Table 1 and Fig. 5). The number of samplings is so large that the core-sampling method may be considered unsuitable for the estimation of root weight. 7. Position C is the best for the survey of the root distribution in different soil layers because twenty four samplings are required within a limit statistic error of 10%, but within a 20% error only seven samplings are required (Table 1, Table 2). 8. As the root weight is greatly influenced by the depth of plow layer, we need to examine beforehand the plow layer depth of the paddy field. 9. Judging from the results, newly developed core-sampler and the soil cutter, especially the latter, proved to be very useful and convenient tools for the investigation on the root system of rice plants in a paddy field.
