Improvement of acid-soil stress factors considering of the secondary mineral composition.

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(1)The acid mineral soils studied were classified four groups : (A)Volcanic ash soils(Chookai, Gassan) ; rich in allophane, gibbsite and Fe-and Al-oxides, high pHo(ca. 5), low ex. Al, steeply increase of CEC above pH 5 and high AEC at low pH but negligible AEC at neutral. (B)1 : 1 type clay mineral acid soils(Matsune, Kinpou) ; rich. in metahalloysite, intermediate pHo(4.3)and moderately high AEC at low pH. (C)2 : 1 type-clay mineral acid soils(Byakko, bewa) ; predominantly of smectite, low pH6(3.8)and extremely high ex. Al, negligible AEC but the highest CEC(30 cmol). (D)Acid sulfate soils(Numanokura, Betto) ; predominantly of smectite, contained high Ca・Mg・ K and SO^2-_ relatively low pHo(4.1), similar tendency of CEC and AEC to the group(C)soils but lower CEC(20 - 25 cmol).(2)Lime application could 'not increase available P(Truog P)in all acid soils but Matsune.(3)To increase plant growth by the application of gypsum, . : applied soils should be rich in allophane, gibbsite, Fe- and Al- oxides, high ZPC, and large AEC at low pH. In such soils, though containing vermiculite, kaolinite and illite, so^2-_ in applied gypsum increased pH(H_2O), decreased H_2O soluble and ex. Al, and increased H_2O soluble and ex. Ca. On the contrary, in the group(C)soils a heavy application of gypsum decreased pH(H_2O), and considerably increased H_2O soluble Al ; although ex. Al did not change and H_2O soluble and ex. Ca increased, Al toxicity was developed and K deficiency was induced and finally decreased in plant growth.(4)The best estimation method of phytotoxic Al in a range of acid soils was the extraction with 0.2M NH_4Cl ; bioassay method, i. e., Al content in the top of sugar beet, was recommended in the case of acid soils including organic soils.