Date of Award

1985

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Abstract

Adsorption and movement of R. japonicum strain 110 in soils was studied under laboratory conditions. Vertical movement of rhizobia as affected by precolating water was examined in sand and silt loam soils. Rhizobia did not move vertically when the soils were already at field capacity; however, percolating water enhanced the movement. Soil texture and clay concentration affected the movement of rhizobia. They moved readily in a sand but the migration decreased with increasing depth in a silt loam. Rhizobial movement decreased as clay content increased. The bacteria remained in the first 4 cm when 12% clay was used. In the absence of percolating water, rhizobia traveled only 4 cm with emerging soybean roots but were transported with water when it was added after the inoculated seeds were planted in soil columns. Lateral movement of rhizobia followed the water flow pattern as it moved away from the inoculation point. The linear relationship between rhizobial number and distance moved indicated that vertical movement was greater than lateral movement. Adsorption of rhizobia by soil particles was found to be one of the major mechanisms responsible for lack of movement. Adsorption increased as particle size decreased. Clay had a very large capacity to adsorb rhizobia. Montmorillonite adsorbed twice as many cells as kaolinite under similar conditions. Adsorption increased as clay content increased. Also the adsorption was affected by rhizobial concentration. The number of rhizobia adsorbed increased as the rhizobial concentration increased. However, percent adsorption decreased as rhizobial concentration increased. Montmorillonite clay, saturated with Na('+), K('+), NH(,4)('+), Ca('+2), Mg('+2), Fe('+3), or Al('+3), caused increased adsorption as the valency of saturated cations increased from the mono-, to the di-, and to the trivalent Fe('+3), but not Al('+3). Adsorption by montmorillonite, saturated with mono- valent cations, was lower than by the untreated clay. Adsorption by kaolinite increased when the surface was saturated with the mono- and divalent cations. Adsorption values were 7.5%, 15%, 35%, and 38% for rhizobial sorption by humic acid, corn starch, rice straw, and calcium phytate, respectively. Adsorptions prevented the rhizobia from moving with the root, thus affecting nodule formation.

Pages

144

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