Nitrogen fixation 34 Bacteriology 24 Bacteria 22 Nitrogen 14 Plant physiology 12 nitrogen fixation 10 Nitrogen Fixation 6 Fixation 5 NITROGEN FIXATION 5 Nitrogen-fixing microorganisms 5 Nitrogen-fixing plants 5 Soil Biology 5 Agricultural microbiology 4 Legumes 4 Nitrification 4 Plants 4 Agricultural Microbiology 3 Agroforestry 3 Biofertilizers 3 Biofertilizers-congresses 3 Nitrogen fixing bacteria 3 Nitrogen-Fixation 3 Photosynthesis 3 Plant Nutrition 3 Symbiosis 3 Trees 3 Woody plants 3 biological nitrogen fixation-congresses 3 hydraulic conductivity 3 Agroforestry and Multipurpose Trees: Community, Farm and Social Forestry 2