Organic matter and inoculation with Azospirillum on nitrogen incorporation by field grown maize

Abstract

A field trial using a soil which had not been cultivated for many years, was designed to show the effect of inoculation of Azospirillum spp, on N incorporation and grain production by maize (Zea mays L.) plants. The organic matter and N fertilization interactions were also taken into consideration. The effect of inoculation with a homologous strain (isolated from maize roots) was highly significant for dry weight and total N in plants while inoculation with the heterologous strain (isolated from rice (Oryza sativa L.) roots) had no effect. The increase of total N in the inoculated plants was around 40 kg/ha of N and was not affected by the use of 60 kg/ha of N. Inoculated plants showed an equal or higher increase in total N when compared with the corresponding treatments that had received 60 kg/ha of N under the form of NH₄NO₃. The effect of inoculation of Azospirillum spp. on grain production showed the same trend but was not significant. A 26% increase (600 kg/ha), corresponding to 12 kg/ha of N in grain was observed in the inoculated plants as compared to 1,000 kg/ha in the N fertilized plants. An experiment using pots with the same soil and same treatments showed the preferential establishment of the homologous strain in the roots. Microscopic observations at grain filling stage indicated root xylem infection with TTC reducing bacteria in the inoculated plants.