We investigated that influence of percolation patterns on growth and yield of rice plants and uptake of cadmium from polluted paddy fields using soil dressing models. The experiment was conducted in the green house with open and closed system percolation models (M-1, M-2, M-3, M-4, M-5, M-6, M-7, M-8, M-9 and M-10). Those models were consisted of stratified soil layers and two different percolation systems (open and closed system percolation) and operated by 12.5 cm (M-1 to M-6), 15 cm (M-7 to M-8) and 20 cm (M-9 to M-10) soil dressing with stratified polluted paddy fields. The stratified paddy field models were constructed in an iron box (30x50x70 cm) with three layers of soil; those were plow layer ( layer I; 0-12.5 cm), plowsole (layer II; 12.5-22.5 cm), and subsoil (layer III; 22.5-65cm) and constructed with Andosol or alluvial (layer I), Cd-polluted soil or Cd -polluted soil with alluvial (layer II) and gravel or Cd- polluted soil with gravel (III layer). In open system percolation models was planned in plowsole and subsoil but in the closed system percolation models, soil layers were planed under saturated condition. The two percolation systems were applied to paddy field models by controlling the ground water level at 57.5 cm and 12.5 cm for the open system and closed system model, respectively, using a subsurface drainage pipe.

In open system percolation, the pressure head of the plowsole and subsoil were negative but in closed system showed positive pressure. In the open system percolation models, plowsole and subsoil temperature almost similar to the air temperature but in closed system percolation models were higher than the air temperature. The soil redox (Eh) value in plow layer of both percolations was about -190 mV. But in the plowsole and subsoil were in oxidative condition (650mV) in open system percolation models. On the other hand, in the plowsole and subsoil were in reduction state (-200mV) in closed system percolation models. The average SPAD values in closed system percolation models were lower than the open system percolation models. In the harvesting period, the14th leaf was dry about 78% in closed system percolation but 43% in open system percolation models; this result indicated that the difference of photosynthesis ability of rice plants in two systems during ripening time. Moreover, the plant length, number of stem, number and weight of panicles, number and weight of grains were lower in open system percolation models than the closed system percolation models. Accumulation of cadmium in roots of each soil layer, stem and leaves and rice grain were higher in open system percolation than the closed system percolation models. In soil oxidation state, the insoluble cadmium metal in soil leading to soluble form with presence of oxygen which can be easily uptake by rice plants. As above mentioned, it was recognized that percolation pattern influenced on the growth and yields of rice plants and uptake of cadmium.

（和訳）

　この研究では、浸透型の稲の生育、収量及びカドミウムの吸収に及ぼす影響を汚染土水田の土と客土を用いて調査した。
実験では、開放浸透と閉鎖浸透を持つモデルを10本（M-1～M-10）、ハウス内に作製した。それらの成層モデルは、 客土厚12.5cm（M-1～M-6）、15cm（M-7～M-8）、20ｃｍ（M-9～M-10）。 成層水田は、同一客土厚で、2つの浸透型の影響を比較できるようにした。 その成層水田のモデルは、縦30cm、横50cm、深さ70cmの鉄箱に3層に作製した。 作土層（第Ⅰ層、12.5cm）、鋤床層（第Ⅱ層、12.5cm～22.5cm）、心土層（第Ⅲ層、22.5cm～65cm）の各層は、 作土が黒ボク土あるいは沖積土、鋤床層がカドミウム汚染土あるいは沖積土と汚染土、 心土層が汚染土と礫からなる。 開放浸透モデルは、鋤床層及び心土層を開放浸透に、閉鎖浸透モデルは全層飽和条件とした。 これらの浸透型の制御は、地下水位を開放浸透モデルでは52.5cm、閉鎖浸透モデルで12.5cmとすることで行った。

　圧力水頭は、開放浸透モデルで、鋤床層、心土層が負圧になったが、閉鎖浸透モデルでは正圧を示した。 開放浸透モデルでは、鋤床層及び心土層の地温は、気温に近かったが、閉鎖モデルの同層の値は、気温より高くなった。 作土層の酸化還元電位は、両モデルで約-190mVとなった。 しかし、開放モデルの鋤床層及び心土層では650mVの酸化状態となった。 他方、閉鎖浸透モデルの鋤床層、心土層の値は-200mVとなった。
SPAD値は、閉鎖浸透モデルの稲の値が開放浸透の値より小さくなった。 収穫時の第14葉の黄色く変化した長さは、開放浸透で全長の78%、開放浸透で43%となった。 この結果は、浸透型の相違により光合成能力の違いが生じることを示唆した。 さらに、草丈、茎数、穂重、玄米の粒数と重さは、閉鎖浸透モデルの値が開放浸透モデルの値より低下した。 層別の根のカドミウム濃度、茎葉及び玄米中の濃度は、閉鎖浸透モデルより開放浸透モデルの値が高くなった。 この一因は、酸化条件下で、カドミウムが稲に容易に吸収される形態となることによる。 客土を持つ成層水田おいて、下層が開放浸透か閉鎖浸透かの相違は、稲の生育収量やカドミウムの吸収に影響を及ぼすことが確認された。