RESPONSE OF WHEAT (Triticum aestivum L.) TO DIFFERENT MINERAL NITROGEN LEVELS AND INOCULATION WITH N2-FIXING BACTERIA

Abstract

Two field experiments were carried out on a sandy loam soil at El-Tahrir Province Sector during two successive winter-growing seasons of 2005/2006 and 2006/2007 to study the response of wheat growth, yield and some yield components to inoculation with N2-fixing bacteria under different levels of mineral N-fertilization using sprinkler irrigation system. Wheat seeds (Triticum aestivum L., cv. Sids 1) were inoculated shortly before planting by Azorhizobium caulinodans, Gluconacetobacter diazotrophicus, Bacillus polymyxa as a single treatment or seeds inoculated with mixture of such strains. The tested bacterial strains were interacted with different levels of mineral N fertilizer (zero, 25, 50, 75 and 100 kg N/fed). Nitrogen fertilizer was added in the form of ammonium sulphate (20.5% N). Superphosphate (15.5% P2O5) and potassium sulphate (48% K2O) were added at rates of 200 kg/fed and 100 kg/fed, respectively as a recommended dose. The experimental design was a split plot design with three replications and the plot size was 6 m 2 .Regarding the response to inoculation with N2-fixing bacteria, results of both tested seasons showed that there are significant increases in all wheat vegetative growth, yield and some yield components due to inoculation with any tested diaztotrophs. However, using mixture strains followed by Bacillus polymyxa treatments surpassed other inoculated treatments or uninoculated ones. As general, a comparison between inoculants on all wheat growth aspects as well as wheat yield and its yield components showed the order: Mixture> Bacillus polymyxa> Gluconacetobacter diazotrophicus> Azorhizobium caulinodans> uninoculated treatment.The response of wheat growth, yields and yield components to increasing application rate of mineral N fertilizer was significant. Using higher rates of mineral Nfertilizer (100 kg N/fed) showed higher values of all tested parameters under investigation in both seasons.Taking the interaction between inoculation and different N fertilizer levels into consideration, the best results of wheat growth, yield and its components were achieved when wheat plants inoculated with mixture strains followed by Bacillus polymyxa in combination with 50 kg N/fed, which showed a positive response and gave values nearly similar to or higher than using the full dose of mineral N-fertilizer (100 kg N/fed). This trend was true in both tested seasons.From these results it could be concluded that the inoculation with N2-fixing bacteria, particularly in a mixture form, may be acting as a good practice for enhancing wheat growth aspects and improving the crop yield and yield components. Also, it could compensate 50% of the recommended inorganic-N used in sandy loam soil with no decrease in wheat quantity or quality.