Optimization of Biofertilizers Enriched in N by Diazotrophic Bacteria

Abstract

Free-living diazotrophic bacteria can enrich organic biofertilizer in nutrients to application in sustainable agriculture. The objective of the study was to select diazotrophic bacteria isolated from different soils, evaluated by analyses of nitrogenase activity. The diazotrophic were submitted to gene rRNA 16S sequenced and the best isolates compared with strains used to produce the biofertilizer. The biofertilizers used earthworm compost and sugarcane mud cake mixed with PK rock biofertilizer in different proportions (3:2:1 and 2:3:1). The experiment conducted in a factorial 6x2x2, used six diazotrophic bacteria applied in two concentrations (100 and 200 mL) and organic matter in the selected proportions, with four replicates. Samples were collected in times 0; 10; 20; 30 and 40 days and analyzed: pH (H2O), total C, total N, available P and K. The rRNA 16S gene sequence identified the selected diazotrophic as Bacillus, Mesorhizobium, Paenibacillus and Beijerinckia. The strains increased nutrients in the biofertilizers, especially the isolate NFB 4 and strain NFB 1003, in incubation time of 25 and 30 days. The more effective diazotrophic increased nutrients, especially N in biofertilizer produced in proportion 3:2, and promoted significant interaction for all analyzed parameters, except to total C. Available P and K increased when applied in both proportions. The selected diazotrophic bacteria produce biofertilizers that may be used as alternative substrate to replacement of soluble fertilizer.

Keywords: Biofertilizers; free-living diazotrophic; nutrient enrichment; organic matters; rock biofertilizers; sugarcane mud cake