Potential for nitrogen fixation and biomass production in Panicum maximum

Abstract

Investigations were carried out to ascertain the relationship between the potential for biomass production and nitrogenfixation in tbe rhizosphere of Panicum maximum. With a dry matter production of 1.85 ± lAO and 0048 ± 0.33 kgm^-2, a positive correlation (1=0.62) was found to exist between the numbers of nitrogen-fixing bacteria in the rhizosphere of this grass and total dry matter production. The influence of concentrations of organic carbon substrates in roots/ rhizomes on total bacterial populations was also investigated. Results showed that increasing concentrations of organic acids, reducing sugars and miscellaneous soluble carbohydrates at naturally-occurring levels were accompanied by reductions in bacterial population. Aerobic nitrogen-fixing bacteria appeared to play the most dominant role as viable counts of these bacteria were about four times higher than those of their anaerobic counterparts. Azospirillum sp. contributed approximately 48 per cent of total aerobic counts and was found to be capabl e of growth under strictly anaerobic conditions where it constituted about 11 per cent of total counts. Panicum maximum was found to be capable of growth in soils of clay-loam, sandyclay or purely loam types with pH 5.0-5,9. The ammonium nitrogen levels in these soils were relatively low when compared to those of nitrite-nitrogen.