Effects of Inoculation Rate, Rhizobia1 Strain Competition, and Nitrogen Fixation in Chickpea
- Padma Somasegaran ,
- Heinz J. Hoben and
- Velittin Gurgun
Chickpea (Cicer arietinum L.) is the third most widely cultivated legume in the world, but N-fixation studies addressing its inoculation response and rhizobial strain competition are limited. We investigated N fixation and competition by three strains of chickpea Rhizobium (TAL numbers 480, 620, and 1148) on ‘Desi’ and ‘Kabuli’ chickpea genotypes grown in vermiculite and two soils (Ultisol and Oxisol) free of chickpea rhizobia. Chickpea grown in vermiculite was inoculated with single and mixed strains. A three-strain mixture was inoculated at 10, l02, l04, l06, and l08 rhizobia per seed on seeds planted in the two soils. Nodulation and N-fixing parameters were significantly different for chickpea genotypes and rhizobial strains, with no genotype × strain interaction in the vermiculite experiment. TAL 620 was the most competitive strain in both chickpea genotypes. Maximum N fixation in both genotypes was achieved at lo4 and 10" rhizobia per seed in the Ultisol and Oxisol, respectively. Nitrogen fixation by chickpea in response to different inoculation rates was best described by a quadratic model. The three strains of Rhizobium competed differently in the two soils. Competition in the Ultisol was due to significant strain differences and genotype x strain interaction. In the Oxisol, there was no strain competition. Different inoculation rates did not influence strain competition. In general, the Kabuli genotype had a greater N-fixing potential than the Desi. Maximum N fixation in the two soils was a function of the different inoculation rates for both genotypes. Competition among chickpea rhizobia was influenced by the growth medium, chickpea genotypes, and strain differences but not inoculation rates.
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