Green Manuring Nodules Bacterial Diversity and Its Relation with the Origin Soils from Sugarcane Growing Regions of the Brazilian Northeast.

Nitrogen fixing bacteria and legume green manuring may achieve high sugarcane yields with lower environmental degradation. Rhizobial diversity knowledge may help to understand inoculation response under different soil and climate conditions. This work aimed to evaluate rhizobial diversity for crotalaria (Crotalaria spectabilis) and sunhemp (Schizolobium aterrimum) from sugarcane growing soils. 260 soil samples were collected at Alagoas, Pernambuco and Paraíba, and their chemical, physical and meteorological characteristics determined. Crotalaria and sunhemp seedlings were cultivated in Leonard jars with sand:vermiculite (1:1) mixtures and 1g of each soil sample was used as inoculant to obtain nodules. At 60 days, nodules were collected and crushed on Petri dishes with YMA media for isolation and morphological characterization. Similarity dendrograms for all isolates were determined based on morphophysiological characteristics for each legume species and Shannon-Wiener, Simpson and Pielou indexes were calculated. Isolates were authenticated in their respective legume species in a similar manner to the first experiment. 5 mL of each isolate grown on YM media were used as inoculant. 108 and 39 crotalaria and sunhemp isolates were authenticated. Most isolates were fast grower with high mucus production. Dendrograms present high morphological diversity forming 87 and 30 crotalaria and sunhemp groups, most with a single isolate. Different bacteria groups from a single soil were associated to crotalaria and sunhemp. Soil pH, Na, Ca, Mg, K, Al, OC, sand, silte and clay contents explained half the variation between the soil groups. There was no relation between soil characteristics and morphological characteristics of the isolates.