Effect of Calcium Carbonate on the Cadmium Content of Wheat after Addition of Large　Ammount of CdS to Soil

In Japan, wheat is usually cultivated from December to June as a second crop in the same field as rice. In Cd-polluted areas, the fields are affected by both wastewater and the emissions from the chimneys of zinc refineries or plating factories. The application of inhibition agents, such as slaked lime, calcium silicate or fused magnesium are applied to inhibit the absorption of these metals by plants. Many reports have been made on the decrease of metal absorption through the application of some form of calcium, phosphate or silicate. Also, it has been reported that wheat is more sensitive to CdS than to CdO. However, almost all experiments were performed at less than 500 ppm Cd in soil, and these experiments have not been made at a concentration close to the level critical for wheat plants. There have been few reports on the effects of calcium cabonate on metal tolerance or metal uptake at the a level critical wheat. The typical example of using calcium carbonate was investigated by Maeda, and the application of phosphate by Koshino, and by Muramoto et al. The effects of calcium carbonate on the metal content of wheat to the critical levels were examined.

植物に対する有害金属の生育限界濃度域での実験は極めて少ない。ここでは、小麦の硫化カドミウム（CdS）に対する生育限界濃度と小麦穀粒中カドミウム含有量に及ぼす炭酸カルシウム添加栽培の影響を調べた。その結果、硫化カドミウムに対する小麦の生育限界濃度は1,500ppmであり、その時の小麦穀粒中のカドミウム含有量は123.2μg/g（乾燥物中）であることが判明した。すなわち溶解度の低いカドミウムの化学形においても、穀粒中への集積が生じる結果が表示された。また、炭酸カルシウムの同時添加により、無添加に対して1,500ppm区では穀粒中のカドミウム含有量は57％減少し、小麦の生育限界濃度5,000ppmに拡大された。茎葉長、茎葉重、穀粒重等の各生育項目において炭酸カルシウムの添加効果が見られ、特にカドミウム濃度500-5,000ppmの間では炭酸カルシウム添加によるカドミウム毒性の抑制現象が有意に認められた。このことは高濃度カドミウム汚地域における炭酸カルシウムによる植物保護の一策としての有効性を示唆したと考えられる。