養液栽培培地におけるリン酸一水素カルシウムなどの沈でん生成機構とその防止対策

概要

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The preventive measures of calcium phosphate precipitation in nutrient solution for hydroponic cultivation were discussed as follows. The formation period, the pH an ion strength which precipitate calcium phosphates (CaHPO_4・2H_2O : brushite ; CaHPO_4 : monetite ; Ca_8H_2(PO_4)_6・5H_2O : OCP) in the Japanese standard solution which is typical composition in Japan were examined. The nutrient solutions were prepared pH 6.4, 6.6, 6.8, 7.0, 7.2 and 7.4 by addition of KOH and ion strength values from 0.023 to 0.045 by addition of KNO_3. The results were summarized as follows. 1) The precipitation of calcium phosphate and more than 80% of appended Mn was complete in the period of 24 hours after the set up of the condition of nutrient solution in which pH was 7.4 and ion strength was 0.040. 2) The precipitation of calcium phosphate was dependent upon pH, p(HPO_4^<2->) and p(Ca^<2+>) of nutrient solution and was found above the condition of nutrient solutions in which pH was 6.6, p(HPO_4^<2->) was 3.91 and p(Ca^<2+>) was 2.70. 3) From the discussion on the calculations of thermodynamic condition of solubility equilibrium of calcium phosphate in Japanese standard solution, brushite, monetite, and OCP precipitated above pH 6.8, 6.6, 6.4, respectively. 4) The preventive measure of calcium phosphate precipitation in nutrient solution for hydroponic cultivation were considered that the pH of nutrient solution was maintained under pH 6.4.
1993-06-05