Nodulação do caupi (Vigna unguiculata) e eficiência da comunidade nativa de bactérias diazotróficas de áreas de agricultura familiar no centro-norte maranhense.

Abstract

Among the numerous legume species that benefit from biological nitrogen fixation, Vigna unguiculata (L.) Walp (cowpea) is of special interest as it is largely cultivated in the North andNorth Eastern region of Brazil. The specie is well adapted to local soil and climate conditions and therefore is essential for food safety and basic income for small farmers. The objective of this work was to study the native community of N-fixing bacteria simbiotic with cowpea from different soil management practices in small farmers area from Centre-North Maranhão state. Soil management practices were: slash-and-burn; area with plowing and harrowing a ULTISOL PETROPLINTHIC; 6-y-old alley cropping with Clitoria fairchildiana ; degraded Brachiária brizantha pasture; secondary forest. Rizobia were present in all soil managements nevertheless, alley cropping hosted a rizobia community more efficient to colonize and promote Vigna Unguiculata (L) growth. Cowpea dry biomass was 7.1 g.plant-1 in the 6y alley cropping compared to 0.7g.plant-1 in the control without N. The lowest dry biomass was produced with bacteria from the secondary forest. Seventy-six native isolates were cultivated from soil managements, most of them had low growth rate. Isolates had similar responses to abiotic factors pH, NaCl and temperature. However, the genotype characterization of bacterial isolates showed high diversity and low similarity with the control strains. The isolates of all soil managements were able to nodulate Vigna Unguiculata (L) thus confirming its promiscuity. The 6-y-old alley cropping system was able to stimulate and host a rizobia community more efficient to promote V. Unguiculata growth when compared to the other soil managements