Columbia subject headings:
Harvard subject headings:
Legumes--Handbooks, manuals, etc.
Legumes--Inoculation--Experiments.
Nitrogen--Fixation--Handbooks, manuals, etc.
Nitrogen-fixing microorganisms--Handbooks, manuals, etc.
Rhizobium--Handbooks, manuals, etc.
Symbiosis--Handbooks, manuals, etc.
Princeton subject headings:
Legumes--Handbooks, manuals, etc.
Nitrogen--Fixation--Handbooks, manuals, etc.
Rhizobium--Handbooks, manuals, etc.
Symbiosis--Handbooks, manuals, etc.