Nitrogen fixation potential with Macroptilium of native rhizobial populations in semi-arid Pernambuco, Brazil

Abstract

Nitrogen (N) is one of nature s most abundant elements, accounting for about 78% of the atmospheric gases, but mostly as the inert N2 form. As such it is not directly available to plants, and is relatively scarce in most agroecosystems. Biological nitrogen fixation (BNF) through diazotrophic bacteria represents about 63% of the yearly N input in terrestrial ecosystems (Taiz and Zeiger 2004). Legumes, which form effective symbiosis with the diazotrophic group of bacteria commonly known as rhizobia, are an important source of available N. Tropical forage legumes can usually nodulate with a diverse population of rhizobia, and may make a significant contribution to nitrogen availability in pastures (Santos et al. 2005). Identification and isolation of symbiotically most efficient rhizobial strains would enhance the beneficial effects of legumes in pastures. This could be achieved by quantifying the BNF ability of strains from different regions, vegetation covers, cultivation systems and environmental conditions (Chagas Jr. et al. 2010). Native legumes, including several species of Macroptilium, are an important forage resource in the semi-arid northeast of Brazil, contributing to the quality of ruminant diets, but with unquantified BNF ability. This study evaluated nodulation efficiency of Macroptilium lathyroides, when inoculated with Litolic Neossols from 8 municipalities of the semi-arid Pernambuco State.