SOIL FACTORS REPRESSING ESTABLISHMENT of DINITROGEN FIXING SYSTEM in Phaseolus vulgaris L..

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Soil factors repressing nodule establishment on the roots of Phaseolus vulgaris seedlings were investigated by comparing the plants cultured on field soils and artificial vermiculite. Significant differences in physical and chemical properties between field soils and vermiculite were as follows :a. Exchangeable Ca and particularly Mg were much less in the soils than in vermiculite, and their concentration in water phases was the contrary,b. Nitrate nitrogen was more abundant in the soils than vermiculite, andc. Particule-size distribution in vermiculite was more biased to larger than in the soils.The rate of nodule meristem formation till 10 days after sowing was much less in plants cultured with soil than in vermiculite plants, and the difference was more prominent on secondary roots comparing to that on tertiary one. Differences of chemical properties among field soils affected to formation and setting of nodule meristem on tertiary roots rather than on secondary roots. And, a portion of meristems once appeared on tertiary roots was disappeared by a certain soil condition.Mg and Ca supplement into a field soil gave slight increase of nodule meristem formation. Whereas the dissimilarity in exchangeable or soluble Mg and Ca content between soils and vermiculite was not a primary factor bearing the difference in the meristem formation between soils and vermiculite.Though lowering soil nitrate level significantly recovered repression on the meristem formation in secondary roots, additional repressive factors were estimated to be.There was no linear relationship between nodule meristem formation and particle-size of a tested field soil. However, it was suggested by comparison of nodule meristem formation among plants cultured with vermiculite, perlite and the soil that relatively low air permeability of the soil was a factor repressing nodule meristem formation.