مجله آب و خاک (Feb 2016)
Effect of Combined Application of Phosphate Solubilizing Bacteria and Phosphrous Fertilizer on Growth and Yield of Sesame
Abstract
Introduction: Phosphorus (P) is considered to be one of the most essential macro elements required for growth and development of plants, but, due to low solubility and fixation in soils, only a small fraction of phosphorus in soil (1 ppm or 0.1%) is readily available to plants. chemical fertilizers are widely used in meeting the phosphorous need of crops. However, as the fertilizer production is dependent upon fossil energy sources, continuous use of chemical fertilizers has become a matter of great concern, not only because of the diminishing availability of costly inputs but environmental concerns also. Under this background, it has obviously brought the subject of mineral phosphate solubilization in the forefront. A group of soil microorganisms is recognized to be involved in microbial phosphate solubilization mechanisms through which insoluble forms of inorganic and organic phosphates convert into soluble forms (HPO4-2 or H2PO4-). Acidification of the medium, chelating, exchange reactions and production of various acids has been discussed as the key processes attributed to the conversion. Phosphate solubilizing bacteria (PSB) are a group of plant growth promoting rhizobacteria (PGPR) that convert unavailable forms of phosphorus to available forms and it helps to the growth and yield of plant. The use of plant growth promoting rhizobacteria (PGPR) is considered one of the most important factors increasing sesame yields. Therefore, the aim of the present study was to investigate the interactive effects of PGPR and phosphorus fertilizer on some growth parameters and components of yield and also phosphorus and Zinc uptake in sesame. Materials and Methods: In order to investigation of the effect of combined application of phosphate solubilizing bacteria and phosphorus fertilizer on growth and yield of Sesame, a greenhouse experiment was conducted as factorial based on completely randomized design with three replications including five levels of phosphorous fertilizer (0, 100, 200 and 400 kg ha-1 of triple superphosphate and 1200 kg ha-1 of rock phosphate) and three bacterial levels (inoculation with two phosphate solubilizing fluorescent pseudomonad, isolates of P3 and P5 that known in this study as B1 and B2 and non-inoculated). It should be noted that rock phosphate used in this study has contained 4% of zinc oxide. The bacteria selected from microbial bank of Vali-E-Asr University were able to dissolve the insoluble phosphate and produce siderophore and IAA. Four months after planting, plants were cut at the soil surface, and shoot dry weight, stem height, number of Seeds in pot, seed dry weight and seed oil percentage were recorded. Also phosphorus and Zinc contents in shoot were determined. Results and Discussion: Results indicated that both bacteria (B1 and B2) significantly increased shoot dry weight and B1 increased seed dry weight. Also application of phosphorus fertilizer significantly increased shoot dry weight and plant height. 200 kg ha-1 of triple superphosphate had highest shoot dry weight and was similar with rock phosphate. Combined application of Phosphorous fertilizer and phosphate solubilizing bacteria increased shoot dry weight. Results also showed that seed oil was increased by application of Phosphate rock. Phosphorus concentration in seed was increased with Using B1 and B2 isolates. Application of B2 significantly increased phosphorus concentration in seed (11.5%) and Phosphorous fertilizer levels increased concentration of P and Zn in seed. Application of 200 and 400 kg ha-1 triple superphosphate had the highest concentration of P and Zn in seed. Phosphorus fertilizer levels significantly enhanced uptake of P and Zn in shoot. Application of 200 and 400 kg ha-1 triple superphosphate led to increased uptake of phosphorous in shoot. Also rock phosphate significantly increased uptake of Zn in shoot. Combined application of Rock phosphate and bacteria of B1 and B2 had more significant effects on uptake of Zn in shoot. Conclusion: this study showed that Phosphate solubilizing bacteria (B1 and B2) had significant effects on the growth and nutrient uptake especially phosphorus and zinc in sesame. The simultaneous application of Phosphate rock and Phosphate solubilizing bacteria increased most of the measured parameters similar to the highest levels of triple superphosphate. Therefore, because of high cost of chemical fertilizers production and its environmental problems, application of less levels of phosphorus fertilizers or rock phosphate along with Phosphate solubilizing bacteria could be an appropriate option to avoid wasteful consumption of phosphorus fertilizers.
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