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Abstract Biological nitrogen fixation ”BNF” is the natural environmentally safe process by which such major nutritional element is converted from its gaseous state to a combined form in soil, firstly for the benefit of plants and subsequently of the other living organisms. Such process known as ”Diazotrophy”, is undertaken by a variety of soil microorganisms, i.e., bacteria, actinomycetes and cyanobacteria. Bacteria are the major group in this concern, among them there are the chemo-organotrophic aerobic and anaerobic, symbiotic, associative and free-living members. In order to achieve appreciable benefits from the dinitrogen fixation, it is practically recommended to inoculate the proper plants with the responsible agents. Introduction of diazotrophs into agricultural soils is performed via certain materials carrying the diazotrophic organisms known as ”Bacterial carriers”. Efficiency of the N2-fixation process depends not only on the fixer power, but also on the carrier type. The present work was planned to compare among some materials to ascertain their potentiality to serve as carries for dinitrogen fixing bacteria, using specific culture media. Combinations among the diazotroph carriers were then examined in greenhouse experiments, to declare their contribution to plant growth traits. The carriers used were: Standard (vermiculite 90% + peat 10%), compost, biogas manure and filter mud (sugar industry residue). The diazotroph inocula included the legume-symbiotic Bradyrhizobium and the cereal-associative Azospirillum. The crops tested were the legume peanut and the cereal maize. Pot experiments were performed using two types of soil, i.e., sandy and calcareous. The plant growth traits measured included the dry biomass yield and NPK contents of roots and shoots of both crops, at 30 and 65 days from sowing. As well as, number of bacterial nodules formed on peanut plant roots was counted. The results gained were as follows: I. The Laboratory Experiment ” Influence of Various Bacterial Carriers on Survival of Certain Diazotrophs” Data obtained revealed the following order of priority, among the studied bacterial carriers, as to the preserve the viability of both inoculating diazotrophs cultured on specific media, at succeeding intervals of storing the inoculated carriers continued up to 90 days : compost > biogas manure > standard > filter mud. Prestrelization of the carrier materials suited the survival of the inoculating N2-fixers along a storage period lasted for the 90 days. II. The Greenhouse Experiments (detections were made at 60 and 120 days after planting): presterillized carriers inoculated with each diazotroph, either fresh (7 days) or stored (for 2 months), were tested. Two experiments were executed in order to study the effect of growth traits of plants grown on potted sandy and calcareous soils. The treatments inocluded : controls (without and with recommended doses of NPK mineral fertilizers), standard carrier (100%) + mineral fertilizers, standard carrier (50%) + each of the other materials (50%) + mineral fertilizers. A. Bradyrhizobium/ Peanut crop Peanut experiment included the following treatments: 1- Control uninoculated without N-fertilizer ”C0”. 2- Control uninoculated + recommended doses of N (40 kg N fed-1) ”C1”. 3- Inoculation with Bradyrhizobium (Vermiculite 90% + Peat 10 % ) + 20 kg N fed-1. 4- Inoculation with Bradyrhizobium (Vermiculite 50% + compost 50 %) + 20 kg N fed-1. 5- Inoculation with Bradyrhizobium (Vermiculite 50% + biogas manure\50 %) + 20 kg N fed-1. 6- Inoculation with Bradyrhizobium (Vermiculite 50% + filter mud manure 50 %) + 20 kg N fed-1. The obtained results can be summarized as follows: a) Action of soil type on the results generally: The sandy soil excelled the calcareous one in all cases of the study, due to the higher pH value and CaCO3 content of the later. b) Role of bacterial inocula (carrier type and storage period) on: 1- Nodulation Status: Root modules showed their highest numbers with the mixed carrier containing biogas manure, which discerningly followed by those containing compost, then the mixed filter mud and finally the 100% standard one. Storing the inocula, as well as advancing the plant growth period decreased the number of formed root nodules. 2- Plant growth traits (dry biomass yield of roots, shoots and pods and their contents of NPK. The assessed plant criteria showed progressive increases of their values, as a result of materials accumulation as the growth had proceeded. The carrier treatments showed an order of priority similar to that recorded for nodule formation, as to affect the plant measures. Nutrient contents of both plant roots and shoots responded proportionally with the changes in the biomass yield, concerning the influence of carrier treatments, period of the inoculated carrier storage and detection time. Nitrogen showed the prime response to the undertaken treatments, comparing to phosphorus and potassium, respectively, in order. B. Azospirillum / Maize crop Maize experiment included the following treatments: 1-Control uninoculated without N-fertilizer ”C0”. 2-Control uninoculated + recommended doses of N (90 kg N fed-1) ”C1”. 3-Inoculation with Azospirillun (Vermiculite 90% + Peat 10 %) + 60 kg N fed-1. 4-Inoculation with Azospirillun (Vermiculite 50% + compost 50 %) + 60 kg N fed-1. 5-Inoculation with Azospirillun (Vermiculite 50% + biogas manure 50 %) + 90 kg N fed-1. 6-Inoculation with Azospirillun (Vermiculite 50% + filter mud manure 50 %) + 60 kg N fed-1. The obtained results can be summarized as follows: There were no alterations in the result patterns of the various plant traits detected for maize crop than those recorded by peanut crop, concerning the action of the experimental treatments. Differences appearing in the values of the biomass yields and nutrient contents, under the same growth conditions and applied treatments, are actually referred to the nature of each crop genetically and phenotypically. Key words = Microbial carriers, dizotrophy, Bradyrhizobium, Azospirillum, peanut, maize, plant growth, nutrient contents. |