Role of different nirogen fertilizer levels on the development and effectiveness of VA mycorrhizal fungi on maize plants

The effects of five rates of ammonium sulfate [0, 22.5, 45, 90 and 180 kg N fed-1] on the development and effectiveness of vesicular- arbuscular [VA] mycorrhizal fungi on maize were studied in a clay loam soil. N fertilization at the rates of 22.5 and 45 kg N fed-1 increased significantly the percentage of mycorrhizal root colonization in both mycorrhizal inoculated and un-inoculated plants. Increasing the rates of nitrogen fertilization above 45 kg N fed-1 had a negative effect on root colonization by VA mycorrhizal fungi. A significant increase in dry matter production, N and P uptakes of maize plants was obtained as the rate of nitrogen fertilization increased. At a low N fertilization rate [below 45 kg N fed-1], inoculation with VA mycorrhizal fungi increased the dry matter production, N and P uptakes of maize plants. However, there was no significant response in dry matter yield, N and P uptake of maize plants inoculated with VA mycorrhizal fungi as nitrogen fertilized increased above 45 Kg N fed-1

Competition between soybean and cowpea rhizobia and bradyrhizobia in nodulating soybean.

The competitive interactions among four strains that nodulate soybean and cowpea rhizobia were studied in soybean plants grown under pot and field conditions. All the possible combination between the four strains; Bradyrhizobium japonicum USDA 110, Rhizobium fredii USDA 191, Rhizobium spp. [Arachis] strain 1 and Bradyrhizobium spp. [Vigna] strain 2 were studied to obtain single, double, triple and quadruple inocula. Developed plants were examined after 45 and 90 days from planting to record number, dry weight and nitrogenase activity of the root nodules as well as the dry weight and N-content of shoots. Nodule occupancy by the tested strains was also determined by agglutination and double gel diffusion techniques. Data showed that dual inoculation with R. fredii USDA 191 and B. Japonicum USDA 110 showed maximal effects on all tested parameters and provided soybean plants with 75% of its N-requirements. However, no nodules were developed on soybean roots inoculated with Rhizobium spp. [Arachis] strain 1 in single or combined inocula, Bradyrhizobium spp. [Vigna] strain 2 formed effective nodules in both cases