Ecological studies and symbiotic performance of soybean Rhizobia under different cropping system in Northeast Thailand

Date

10-1995

Abstract

Greenhouse and field experiments were conducted to study the effect of soil cropping histories on the response of soybean to seed inoculation In the field experiments, total and introduced rhizobial populations and nodule occupancy were determined. Crop response to reinoculation was studied in the greenhouse. The dynamics of introduced rhizobial as influenced by soil moisture stress and the presence of host plants was also investigated.

The population of indigenous rhizobia in the soils which were never planted to soybean was less than 10 cells/g soil; the introduced rhizobia formed 88-97% of the nodules in these soils. In the soils which had been grown to soybean the number of indigenous rhizobia was 110 cells/g soil in one location and 140 cells/g soil in the other location and percent nodule occupancies were 45% and 20%, respectively.

Soil cropping histories had no significant effect on populations of the introduced bradyrhizobia. Total rhizobial population in the inoculated plots was generally significantly higher than those in the uninoculated plots. They were also higher in the soils with soybean cropping history.

Generally, seed inoculation, regardless of inoculation rates, significantly increased nodulation by twice as much as the uninocu-lated treatments. However, the significant differences were not always obtained in the soils previously planted to soybean. Nodulation was also influenced by soil cropping history. The highest nodulation was found in the soils previously planted to soybean.

Crop responses in terms of shoot total N, shoot dry weight and grain yield were significantly increased by seed inoculation in most cases even in the soils previously planted to soybean. On the other hand, soil cropping histories had no significant effect on these parameters only in one location.

Inoculation of the preceding soybean crop significantly increased nodule dry weight and shoot dry weight of the succeeding soybean. However, no significant effect was observed in other growth parameters. Nodulation, root dry weight and shoot total N were greatly improved by reinoculation of the following soybean crop.

The number of introduced rhizobia in the simulated plots gradually decreased from 2.5 x 104 to 2.5 x 103 cells/g within 11 weeks in the absence of host plant. However, in the plot where the host plant was present , the population increased to nearly the initial level after a 5-week decline. When soil moisture stresses were imposed, drastic decreases of population were observed especially in the plot without the host plant. The initial decreases of population depended on rate of inoculation. High rate of inoculation showed more drastic decrease during the first week as compared to the low inoculation rate.

Document Type

Dissertation

Degree

Doctor of Philosophy in Soil Science

College

Graduate School (GS)

Adviser/Committee Chair

Erlinda S. Paterno

Committee Member

Rodrigo B. Badayos, Wilfredo C. Cosico, Ruben B. Aspiras

Language

English

LC Subject

Soybean--Thailand, Northeastern, Rhizobium

Location

UPLB Main Library Special Collections Section (USCS)

Call Number

LG 996 1995 S72 N58

Notes

Doctor of Philosophy (Soil Science)

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