Interactions among soil microorganisms and bean and maize grown in monoculture or intercropped

Abstract

Differences in crop systems reflect in soil microorganisms and in this work some interactions among agronomically important microorganisms and common bean (Phaseolus vulgaris) and maize (Zea mays) grown in monoculture or intercropped were studied. Under controlled conditions, both bean and maize exudates stimulated rhizobial survival, growth, and nod gene inducing activity, bean nodulation and N accumulation in tissues, and Azospirillum lipoferum survival. After two years with bean and maize in monoculture or intercropped, Azospirillum spp. population was high and did not differ between treatments, while Rhizobium tropici, nitrite oxidizers and soil biomass were favored by bean plants. Rhizobium etli represented, on average, 15% of rhizobial population, except for soils with maize grown alone, where this species was absent, predominating Rhizobium spp., which nodulate exclusively leucaena (Leucaena leucocephala). Soil extracts from the intercropped system showed higher content of nod gene inducing phenolic compounds. Mycorrhizal spore number was not affected by the treatments, although bean in monoculture favored species diversity.