TROPICAL LEGUMES AS IMPROVERS OF RANGELAND AND AGRICULTURAL SOILS

Abstract

Legumes have been used for their nitrogen fixation properties; however, farmers in tropical countries they do not usually use them, because they do not appreciate visible improvement in the soil. The aim of this paper was to analyse the effect of three tropical legumes (Phaseolus vulgaris, Canavalia ensiformis and Clitoria ternatea) on growth promoting microorganisms [Free Life Nitrogen Fixers Bacteria (FLNFB), Azospirillum sp., Azotobacter sp. and Arbuscular Mycorrhizal Fungi (AMF) on the fertility of two rhizospheric soils; one for rangeland use (Ru) and the other for agricultural use (Au). The bioassays were established under a completely randomized design with three replicates per species. The evaluated soil properties were pH; Organic matter, OM; Total carbon, TC; Total nitrogen, N; Useful Phosphorus, P; Cation Exchange Capacity, CEC; and texture. In rhizospheric soil the populations of FLNFB, Azospirillum sp. and Azotobacter sp.; as well as AMF spores were estimated. The results indicate that Ph. vulgaris was the species that showed lower N fixation in Au soil, but higher P content was found in Ru. Ca. ensiformis and Cl. ternatea had higher N fixation, increased CEC, OM and TC. Clitoria ternatea favored the accumulation of OM and TC, promoting CEC, pH and the AMF population. Canavalia ensiformis was the only species to promote differentiated development of Azospirillum sp. and Azotobacter sp. in Ru, showing higher populations with this legume. Therefore, it is recommended that these data can be considered for the conservation of tropical species, both legumes and native microorganisms.

Keywords

• organic agriculture, soil conservation, biological nitrogen fixation, sustainability, fabaceae