Efecto de <i>Arachis hypogaea</i> (Papilloniaceae) y la alcalinidad del suelo sobre bacterias asociadas con nitrógeno y ureasa

Abstract

This work discusses the role that peanut rhizosphere (Arachis hypogaea L.) and soil alkaline condition exert on the dinamic of the bacterial population involved in the nitro gen cyc1e and on the urease activity. Plants were cultivated under natural soil conditions. Rhizosphere samples were taken at regular intervals (every 7 days) during 35 days of the growth of the plant and the rhizosphere effect on the nitrogen transformer and nitrogen-fixing bacteria populations and on the urease activity was as.certained (N° of rnicroorganisms or enzymatic activity of rhizosphere I N° of rnicroorganisms or enzyrnatic activity of soil). The incidence oC amonifying, nitrifying and denitrifying bacteria was deterrnined by the Most Probably Number Method. The Standard Plate Count Method was used to estimate the nitrogen- fixing bacteria. Urease activity was determined by spectrophotometric analysis. The results obtained show that rnicroflora population and urease activity were significatly greater (p < 0.001 ) in the peanut rhizosphere and that plant age exerted a marked rhizosphere effect ( R/S ). The results demostrated that microbial populations were stimulated in the rhizosphere in the following order: symbiotic nitrogen-fixing > non symbiotic nitrogen-fixing > amonifying > denitrifying > nitrifying bacteria. Urease activity was positively correlated with the denitrifying bacteria population (r= 0.93, p< 0.01 ) and with symbiotic (r= 0.91, p < 0.001) and non symbiotic nitrogen-fixing bacteria populations (r= 0.89, p < 0.05). No correlation was found (r= 0.83 ) between the urease activity and the amonifying bacteria associated with this activitY. It can be conc1uded that the alkaline condition of soil plays a significant role in the development of the transformer and nitrogen-fixing bacteria and on the urease activity in the peanut rhizosphere and that the maguitude of the rhizosphere effect (R/S) varies with the developmental stage of the plant