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crops is shown in Table 1. Rhizobia are highly specific when forming nodules in
legume plants, and are classified into seven groups, known as cross-inoculation
groups (Table 2 ). Successful nodulation depends on the availability of a compatible
strain for a particular legume. Native rhizobial populations play a critical role in the
success of inoculated bacteria as the increasing population density of native rhizo-
bia may hinder the persistence of the inoculated strain. Therefore, the inoculated
strain must be efficient enough to compete with the indigenous rhizobia and to
survive and fix nitrogen in the soil environment. In most rainfed areas, legumes of
the cowpea miscellany group have been grown for hundreds of years, and the popu-
lations of native rhizobia are generally adequate both in alfisols and vertisols despite
wide seasonal variation (Venkateswarlu 1992 ; Hegde 1994 ). Inoculation benefits of
rhizobial strains on some leguminous crops have been studied under the All India
Coordinated Research Projects on Pulses, Groundnut (Arachis hypogaea), Soybean
and Dryland Farming. The beneficial effects of rhizobial inoculation on different
crops under dryland conditions are summarized in Table 3.
Table 1 Potential N contribution of N-fixing legumes in Indian soil
Crop Fertilizer N equivalent (kg ha−^1 )N fixed (kg N ha−^1 year−^1 )Residual effect in
succeeding cereal
crop
Alfalfa 100–300 –
Clover 100–150 83
Chickpea 26–63 60–70
Green gram 50–55 30
Groundnut 112–152 60
Guar 37–196 –
Lentil 35–100 18–30
Pea 46 20–32
Pigeonpea 68–200 20–49
Soybean 49–130 –
Source: Subba Rao ( 1988 )
Table 2 Cross-inoculation groups of Rhizobium
Rhizobium speciesCross-inoculation
group Legume types
R. leguminosarum Peas Pisum, Vicia
R. phaseoli Beans Phaseolus
R. trifoli Clover Trifolium
R. meliloti Alfalfa Melilotus, Medicago,Trigonella
R. lupini Lupini Lupinus, Ornithopus
Bradyrhizobium japonocum Soybean Glycine
Bradyrhizobium spp. Cowpea Cajanus, Vigna, ArachisSource: Modified from Majumdar ( 2011 )
M. Grover et al.