Free living diazotrophic bacteria are known to enrich nitrogen of organic matter sources. In this paper we report of experiments using rock biofertilizers mixed with two types of organic matter (earthworm compound and ice cream waste) inoculated with free living diazotrophic bacteria. The earthworm compound and P and K biofertilizers were mixed to form substrates S 1 (earthworm compound 3 dm 3 ? PK biofertilizer 1 dm 3 and waste ice cream 1 dm 3 ); S 2 (earthworm compound 2.5 dm 3 ? PK biofertilizer 1.5 dm 3 and waste ice cream 1 dm 3 L) and S 3 earthworm compound 2.0 dm 3 ? PK biofertilizer 2.0 dm 3 and waste ice cream 1 dm 3 ), and subsequently inoculated (100 mL pot -1 ) with 3 free living diazotrophic bacteria isolated from different Brazilian soils. The control was an uninoculated earthworm compound. Samples were collected at various incubation time (0; 15; 30 and 45 days) and analyzed for total N. Total N concentrations were highest in S 1 , S 2 and S 3 substrates at 34, 27 and 29 days, respectively. The isolate NFB 1001 increased total N in all substrates and the best results were obtained at 34 days in S 1 substrate which contained the highest amount of earthworm compound. The isolates promoted a decline in N content after 30 days of growth, indicating the best time to produce the organic biofertilizer. The organic biofertilizer enriched in nitrogen by free living diazotrophic bacteria is of relevance to organic agriculture.

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