Phosphate solubilizing bacteria

Thirty actinomycete strains were isolated from the rhizosphere of field-grown plants (Trifolium repens L.) and identified by microscopic characteristics, biochemical tests and molecular techniques. The 16S rDNA sequence analysis showed that most of the isolates belong to the Streptomyces genus. These thirty isolates were tested for their capabilities of solubilizing/mineralizing sparingly phosphate sources, N 2 -fixation and/or siderophore production, typical traits of the so-called Plant Growth Promoting Rhizobacteria (PGPR). Phosphate solubilizing ability was widely exhibited by the isolated. All of them produced acid phosphatase and thirteen of them alkaline phosphatase. Ten strains grew in N-free media. Almost all strains produced siderophores, however the production level was in general very low and only the strain Thermobifida MCR24 released considerable amounts of this metabolite. Streptomyces MCR9, Thermobifida MCR24 and Streptomyces MCR26 were selected to test their interactions with arbuscular mycorrhizal (AM) fungi because they produced the highest plant growth beneficial effects among ten isolates preselected as promissory PGPR. The inoculation of AM fungi improved early establishment of MCR9 in clover rhizosphere, and the late establishment of MCR24. The three actinomycete strains improved AM mycelial growth in absence of the test plant, and MCR9 and MCR26 also stimulate AM fungal spore germination. Inoculation of clover plants with either of the selected actinomycetes enhanced plant growth and N acquisition. Co-inoculation of actinomycetes and Glomus mosseae produced synergic benefits on plant growth and MCR9 and MCR24 also on P acquisition. The three selected actinomycetes improve AM formation by clover plants and Glomus mosseae.

Rose-scented geranium (Pelargonium sp.) is a highly valued aromatic crop. Its growth is limited by soil salinity and sodicity stress. Arbuscular mycorrhizal (AM) fungus, phosphate-solubilizing bacteria (PSB), and P fertilizers may enhance the growth and secondary metabolism in geranium plants. In this context, a pot experiment was conducted to study the effects of PSB, AM fungi (Glomus intraradices), and P fertilizer on the yield, chemical composition of essential oil, and mineral element acquisition of geranium. The dry matter yield of shoot and essential oil yield, and mineral element (P, K, Ca, Mg, Na, Fe, Cu, and Zn) uptake in shoot tissues of geranium were significantly increased by the inoculation with AM fungi, co-inoculation with AM fungi and PSB, and P fertilization as compared to control. While the co-inoculation of geranium with AM fungi and PSB significantly enhanced the content of the monoterpenes such as citronellol, geraniol, geranial, and a sesquiterpene (10-epi-γ eudesmol), the P fertilization only enhanced the content of a sesquiterpene, 10-epi-γ eudesmol in the volatile oil. We conclude that the co-inoculation of PSB and AM fungi could be the best natural alternative to phosphate fertilizers to enhance the yield and quality of essential oil from geranium plants grown in sodic soils.

In this study, a total of twenty four phosphate solubilizing bacterial (PSB) colonies were isolated on the Pikovskaya's agar medium from different effluent exposed sediment of river Ganga. The bacteria showing clear halo zones around their colonies were considered as phosphate solubilizers. Out of 24 phosphate solubilizing bacterial isolates, 4 potential isolates showing highest halo zone on Pikovskaya's agar medium were selected for the phosphorus absorption kinetics study. Isolates RPSB6, SPSB13, JPSB16 and TPSB23 belong to genera Pseudomonas, Enterobacter, Bacillus and Flavobacterium respectively as identified by their physiological, morphological and biochemical characteristics. Among these 4 PSB isolates, Bacillus sp JPSB16 showed the maximum P absorption (Vmax) value of 72.4 (10 -4 mg d -1 number -1 ) followed by Flavobacterium sp TPSB23 (65.1), Enterobacter sp SPSB13 (62.2) and Pseudomonas sp RPSB6 (58.7), as compared to 26.3 (10 -4 mg d -1 number -1 ) for the average sediment microorganisms.

Most agronomic soils contain large reserves of total phosphorus [P], but the fixation and precipitation of P cause P deficiency, and in turn, restrict the growth of crops severely. Phosphorus replenishment, especially in sustainable production systems, remains a major challenge as it is mainly fertilizer-dependent. Though the use of chemical P fertilizers is obviously the best means to circumvent P deficiency in different agro-ecosystems, their use is always limited due to its spiralling cost. A greater interest has, therefore, been generated to find an alternative yet inexpensive technology that could provide sufficient P to plants while reducing the dependence on expensive chemical P fertilizers. Among the heterogeneous and naturally abundant microbes inhabiting the rhizosphere, the phosphate solubilizing microorganisms (PSM) including bacteria have provided an alternative biotechnological solution in sustainable agriculture to meet the P demands of plants. These organisms in addition to providing P to plants also facilitate plant growth by other mechanisms. Despite their different ecological niches and multiple functional properties, P-solubilizing bacteria have yet to fulfil their promise as commercial bio-inoculants. Current developments in our understanding of the functional diversity, rhizosphere colonizing ability, mode of actions and judicious application are likely to facilitate their use as reliable components in the management of sustainable agricultural systems.

With the aim to explore the possible role of mineral phosphate-solubilizing bacteria (PSB) in phosphorus (P) cycling in iron-rich, acidic soils, we conducted a survey of PSB naturally colonizing a limonitic crust in the south-east region of Venezuela (Bolı´var State). A total of 130 heterotrophic bacterial isolates showing different degrees of mineral tri-calcium phosphate (Ca 3 (PO 4 ) 2 )-solubilizing activities were isolated from NBRIP plates. In contrast, no isolates showing iron phosphate (FePO 4 )-or aluminum phosphate (AlPO 4 )-solubilizing activities were detected by this experimental approach. The 10 best Ca 3 (PO 4 ) 2 -solubilizers were selected for further characterization. These isolates were shown to belong to the genera Burkholderia, Serratia, Ralstonia and Pantoea by partial sequencing analysis of their respective 16S rRNA genes. All the PSB isolates were able to mediate almost complete solubilization of Ca 3 (PO 4 ) 2 in liquid cultures; in contrast, the PSB isolates were less effective when solubilizing FePO 4 . Two groups of PSB isolates were clearly differentiated on the basis of their Ca 3 (PO 4 ) 2 solubilization kinetics. Acidification of culture supernatants seemed to be the main mechanism for P solubilization. Indeed, gluconic acid was shown to be present in the supernatant of five isolates. Furthermore, detection of genes involved in the production of this organic acid was possible in three isolates by means of a PCR protocol. r

Water samples from the Bandel thermal power plant effluent exposed water of river Ganga at Tribeni West Bengal, India were collected monthly to enumerate phosphate solubilizing bacteria (PSB) population between January 2011 and December 2011. The population density of PSB ranged from 2.07 x10 3 cells ml -1 to 2.57x10 3 cells ml -1 . PSB was highest in the month of July and lowest in the month of February. Out of 24 PSB isolates, 5 isolates exhibiting highest phosphate solubilisation index (SI) ranged from 3.000-2.714. A significant variation (159.84-201.38 µg P ml -1 ) in the capacity to solubilize phosphate by the isolates of PSB was noted. Flavobacterium sp TPSB23 showed highest phosphatase activity of 31.24 µmoles/g/h followed by Bacillus sp TPSR21 (27.12 µmoles/g/h). In all the PSB isolates, decrease in pH was observed in liquid Pikovskaya's medium ranging from 3.66 to 4.17 from initial pH of 7.0±0.2.

Most agronomic soils contain large reserves of total phosphorus [P], but the fixation and precipitation of P cause P deficiency, and in turn, restrict the growth of crops severely. Phosphorus replenishment, especially in sustainable production systems, remains a major challenge as it is mainly fertilizer-dependent. Though the use of chemical P fertilizers is obviously the best means to circumvent P deficiency in different agro-ecosystems, their use is always limited due to its spiralling cost. A greater interest has, therefore, been generated to find an alternative yet inexpensive technology that could provide sufficient P to plants while reducing the dependence on expensive chemical P fertilizers. Among the heterogeneous and naturally abundant microbes inhabiting the rhizosphere, the phosphate solubilizing microorganisms (PSM) including bacteria have provided an alternative biotechnological solution in sustainable agriculture to meet the P demands of plants. These organisms in addition to providing P to plants also facilitate plant growth by other mechanisms. Despite their different ecological niches and multiple functional properties, P-solubilizing bacteria have yet to fulfil their promise as commercial bio-inoculants. Current developments in our understanding of the functional diversity, rhizosphere colonizing ability, mode of actions and judicious application are likely to facilitate their use as reliable components in the management of sustainable agricultural systems.

Biofertilizer is a safe alternative fertilizer instead of various chemical fertilizers for increasing plant productivity which can minimize the ecological damage. There are plant symbiotic-soil bacteria which can solubilize phosphate or produce IAA. The objectives of this research are to determine the best soil bacteria in producing IAA or solubilizing phosphate and to know their roles in promoting plant growth in unfertile soil. As many as 8 isolates of phosphate solubilizing bacteria and 5 isolates of IAA producing bacteria were found. Among those isolates, there were 2 potential isolates (P2 & P4) that were able to solubilize phosphate and 1 potential isolate (I3) that was able to produce IAA. Isolate P4 produced holozone as wide as 1.45 cm and isolate P2 was 1.3 cm. Meanwhile, isolate I3 produced the highest concentration of IAA compared to the other isolates, that was 33.3 ppm. These isolates were applicated further on unfertile soil (yellow soil) as a medium for soybean growth. Soybeans have been grown for 10 weeks to observe the effect of those potential isolates on plant growth and productivity. The result showed that application of isolate I3 was able to promote plant growth and increase plant productivity better than the other isolates as well as controls (fertile and unfertile soil). It promoted the soybean growth such as plant height was 58,8 cm; plant fresh weight was 3.5 g; plant dry weight was 1.55; pod fresh weight was 1.23; pod dry weight was 1.03; the amount of the pod was 3 and the number of the seed was 7.

Most agronomic soils contain large reserves of total phosphorus [P], but the fixation and precipitation of P cause P deficiency, and in turn, restrict the growth of crops severely. Phosphorus replenishment, especially in sustainable production systems, remains a major challenge as it is mainly fertilizer-dependent. Though the use of chemical P fertilizers is obviously the best means to circumvent P deficiency in different agro-ecosystems, their use is always limited due to its spiralling cost. A greater interest has, therefore, been generated to find an alternative yet inexpensive technology that could provide sufficient P to plants while reducing the dependence on expensive chemical P fertilizers. Among the heterogeneous and naturally abundant microbes inhabiting the rhizosphere, the phosphate solubilizing microorganisms (PSM) including bacteria have provided an alternative biotechnological solution in sustainable agriculture to meet the P demands of plants. These organisms in addition to providing P to plants also facilitate plant growth by other mechanisms. Despite their different ecological niches and multiple functional properties, P-solubilizing bacteria have yet to fulfil their promise as commercial bio-inoculants. Current developments in our understanding of the functional diversity, rhizosphere colonizing ability, mode of actions and judicious application are likely to facilitate their use as reliable components in the management of sustainable agricultural systems.

The effect of four phosphate-solubilizing bacteria (PSB), (Burkholderia gladioli 10216, Burkholderia gladioli 10217, Enterobacter aerogenes 10208 and Serratia marcescens 10238) as identified on the basis of 16S rRNA gene sequencing was evaluated on plant growth and commercially important glycosides, stevioside (ST) and rebaudioside-A (R-A) of Stevia rebaudiana in pots containing tricalcium phosphate (TCP) supplemented soil. The PSB were isolated from the rhizosphere of S. rebaudiana plants and tested for P-solubilization ability, biocompatibility, indole acetic acid (IAA) and siderophore production. In greenhouse study, treatment of either individual PSB or a consortium (of PSB) resulted in increased plant growth, ST and R-A contents. The stimulatory effect was observed with consortium treatment in plant growth parameters (shoot length, 22.5%; root length, 14.7%; leaf dry weight, 89.0%; stem dry weight, 76.3% and shoot biomass, 82.5%) and glycoside contents (ST, 150% plant−1 and R-A, 555% plant−1) as compared to the un-inoculated plants. Among individual PSB treatments, B. gladioli 10216 showed most promising response in majority of the parameters studied. The root colonization potential of PSB, assayed by RAPD technique, showed the colonization of all PSB isolates, though their extent of colonization varied.▶ Phosphate-solubilizing bacteria were isolated from the Stevia rhizosphere. ▶ Isolates belong to genera Burkholderia, Enterobacter and Serratia. ▶ Isolates enhanced the plant growth, stevioside and rebaudioside-A content. ▶ Stimulatory effect was observed on the soil and plant phosphorus content. ▶ Consortium treatment showed better results than individual treatments.

Sediment samples were collected from different stations of the Thondi coast, Palk Strait, for the isolation of phosphate solubilizing bacteria (PSB) and to estimates the physico-chemical parameters between October 2008 to March 2009. PSB population ranged between 0.80-2.56x10 4 cells g -1 . Pseudomonas, Bacillus, Vibrio, Micrococcus, Flavobacterium, Corynebacterium, Alcaligenes and Enterobacter were isolated. Pseudomonas and Bacillus were found to solubilize more phosphates than others. Further phosphate solubilizing activity and solubilization index were also monitored. The phosphate solubilizing potential of Pseudomonas sp was confirmed as a proficient solubilizer than others, where P solubilization was 1670 µg ml -1 associated with reduction of pH. These bacteria were found to be highly adaptive and therefore, can significantly contribute to the phosphate economy of the marine environ.

Agricultural soils in Iran are predominantly calcareous with very low plant available phosphorus (P) content. In addition to their beneficial N 2 -fixing activity with legumes, rhizobia can improve plant P nutrition by mobilizing inorganic and organic P. Isolates from different cross-inoculation groups of rhizobia, obtained from Iranian soils were tested for their ability to dissolve inorganic and organic phosphate. From a total of 446 rhizobial isolates tested for P solubilization by the formation of visible dissolution halos on agar plates, 198 (44%) and 341(76%) of the isolates, solubilized Ca 3 (PO 4 ) 2 (TCP) and inositol hexaphosphate (IHP), respectively. In the liquid Sperber TCP medium, phosphate-solubilizing bacteria (Bacillus sp. and Pseudomonas fluorescens) used as positive controls released an average of 268.6 mg L )1 of P after 360 h incubation. This amount was significantly (P < 0.05) higher than those observed with all rhizobia tested. The group of Rhizobium leguminosarum bv. viciae mobilized in liquid TCP Sperber medium significantly (P < 0.05) more P (197.1 mg L )1 in 360 h) than other rhizobia tested,. This group also showed the highest dissolution halo on the TCP solid Sperber medium. The release of soluble P was significantly correlated with a drop in the pH of the culture filtrates indicating the importance of acid production in the mobilization process. None of the 70 bradyrhizobial isolates tested was able to solubilize TCP. These results indicate that many rhizobia isolated from soils in Iran are able to mobilize P from organic and inorganic sources and this beneficial effect should be tested with crops grown in Iran.

In the present study, the antibacterial potential of a phosphate solubilizing bacterium isolated from the river Ganga, West Bengal, India was investigated. Experimental studies found that the strain KUPSB12 was effective in phosphate solubilization with phosphate solubilization index of 2.85 in Pikovskaya's agar plates along with very high soluble phosphate production of 219.64 ± 0.330 mg mL
1 in liquid medium. The phosphate solubilizing bacterium was identified using physiological, morphological and biochemical
characters as well as 16S rRNA gene sequencing. The phosphate solubilizing bacterium was identified as a strain of Pseudomonas aeruginosa. The antibacterial activity of the cell-free filtrates of this isolate was evaluated against three Gram negative bacteria (Escherichia coli MTCC 443, Shigella flexneri MTCC 1457 and Vibrio cholerae MTCC 3904) and three Gram
positive bacteria (Bacillus subtilis MTCC 441, Micrococcus luteus MTCC 1538 and Staphylococcus
aureus MTCC 3160). P. aeruginosa KUPSB12 strain showed the wide inhibitory spectrum against all tested pathogenic bacterial stains. Among the bacteria tested M. luteus MTCC 1538 was found to be most susceptible (19.33 ± 0.33 mm) to the cell-free filtrates of this isolate. These findings suggest that the identified strain may be utilized for screening the antibacterial substances to formulate new treatments for infections caused by pathogenic bacteria.

Phosphates solubilizing bacterial (PSB) strains were isolated from the jute mill effluent discharge area of the Ganga river water at Bansberia, West Bengal, India. Experimental studies found that the strain KUPSB16 was effective in solubiliza-tion of phosphate with phosphate solubilization index (SI) = 3.14 in Pikovskaya's agar plates along with maximum solubilized phosphate production of 208.18 g mL-1 in broth culture. Highest drop in pH value was associated with maximum amount of phosphate solubilization by the PSB strain KUPSB16 where pH decreased to 3.53 from initial value of 7.0±0.2. The isolated PSB strains were tested for tolerance against four heavy metals such as cadmium (Cd), chromium (Cr), lead (Pb) and zinc (Zn) at concentrations 1-15 mM. The results showed that most of the PSB isolates grew well at low concentrations of heavy metals and their number gradually decreased as the concentration increased. Isolated PSB strain KUPSB16 was tested for its multiple metal resistances. Minimal inhibitory concentrations (MIC) for Cd 2+ , Cr 6+ , Pb 2+ and Zn 2+ in tris-minimal broth medium were 4.2, 5.5, 3.6 and 9.5 mM respectively. The MIC values for the metals studied on agar medium was higher than in broth medium and ranged from 4.8-11.0 mM. The isolated bacterial strain KUPSB16 was subjected to morphological, physiological and biochemical characterization and identified as the species of the genus Bacillus. The phosphate solubilizing bacterium possessing the properties of multiple heavy metal tolerance in heavy metal contaminated areas might be exploited for bioremediation studies in future.

The effect of seed inoculation by phosphate solubilizing microorganisms and different levels of phosphorus chemical fertilizer on forage and grain quality of barley (Karoon x Kavir cultivar) was studied in Experimental Farm of College of Agronomy and Animal Sciences, University of Tehran during 2006-2007 growing seasons. Three phosphorus fertilizer levels of 0 (control), 30 and 60 kg ha were allocated to the main 1 plots and three levels of Phosphate solubilizing bacteria of 0 (control), Pseudomonas petida accessions number 9 and 41 along with two levels of Mycorrhiza: with and without Mycorrhiza (control) were assigned to the subplots in a factorial combination. Applications of sole bacteria (accession 41) significantly decreased neutral detergent fibers (NDF) (57.4%) in barley forage. The maximum grain protein (11.37%) was obtained with application of sole Mycorrhiza. The same treatment also could increase Ash to an acceptable level (8.05%). NDF was significantly (p<0.05) decreased while WSC was increased by application of chemical phosphorous fertilizer. Sole and co-application of Mycorrhiza and bacteria had a significantly positive influence on increasing the percentage of grain protein and Ash and also decreasing the NDF value. The application of these inoculants could be considered as an appropriate substitute for chemical phosphorous fertilizer in organic and sustainable agricultural systems.

Freedom from hunger is a fundamental human right. As such, it is intrinsically linked to, as well as essential for, the full enjoyment of other rights such as health, education, and work, and everything that emanates from them. Nevertheless, according to recent estimates from the Food and Agriculture Organization of the United Nations (FAO), more than 923 million people are chronically hungry, most of them in rural areas of poor countries (FAO 2005). The number of hungry people is steadily rising, having increased by about 50 million in 2007 alone. If world population continues to grow at the mean estimated annual rate of 1.1%, it will reach 7.4 billion by 2017. In 2050, it will head towards 9.3 billion people (FAO 2005). Therefore, the world urgently needs a second Green Revolution-sometimes referred to as the "Gene Revolution"-in order to increase food production by at least 50% in the next 20 years. The challenge we are facing is enormous. Two of the requirements for producing additional food are of paramount importance. First of all, agriculture productivity must significantly increase, particularly in the lesser developed, tropical regions of the world. The second condition is that the agricultural frontier be expanded into regions considered as marginal lands, consisting of fragile soils with a lower productive capacity and a higher risk of degradation (Zapata and Roy 2004).

The efficiency of 13 phosphate-solubilizing bacteria (PSB; four Burkholderia sp., five Enterobacter sp., and four Bradyrhizobium sp.) was assessed in a soil plate assay by evaluating soil phosphorus (P) availability. A commercial argentine strain, Pseudomonas fluorescens, was used for comparing solubilizing activity. Burkholderia sp. PER2F, Enterobacter sp. PER3G, and Bradyrhizobium sp. PER2H strains solubilized the largest quantities of P in the soil plate assay after 60 days as compared with the other strains, including the commercial one. The effect of PSB inoculation on growth and nutrient uptake of soybean plants was also studied under greenhouse conditions. Plants inoculated with Burkholderia sp. PER2F had the highest aerial height and showed an appropriate N/P ratio. However, none of the PSB increased P uptake by plants. This suggests that PSB inoculation does not necessarily improve P nutrition in soybean, nor was there any relationship between P availability in the soil plate assay and P content in the soybean shoot in the greenhouse. We concluded that the selection of efficient PSB strains as possible inoculation tools for P-deficient soils should focus on the integral interpretation of soil assays, greenhouse experiments, and field trials.

— A field experiment was conducted in Summer-Spring cropping season 2016 at Cujut district, DakNong province, Vietnam to study the effects of rhizobia and phosphate-solubilizing bacteria (PSB) on soybean (cv. Cujut) cultivated on ferralsols. The experiment consisted of six treatments as follows: control (no fertilizer, no inoculant), 240 kg/ha NPK 15-15-15, rhizobial inoculant [with liquid cover seeds] + 20 kg N/ha applied at 10 days after sowing [DAS], PSB inoculant [with liquid cover seeds] + 20 kg N/ha at 10 DAS, rhizobial and PSB inoculant [with liquid cover seeds] + 400 kg fertilizer/ha + 20 kg N/ha at 10 DAS and endophytic bacteria inoculant [with liquid cover seeds] + 400 kg fertilizer/ha + 20 kg N/ha at 10 DAS from June to August, 2016. The results showed that application of rhizobial inoculant and/or PSB inoculant produced significantly higher yield component, grain yield than control and did not differ from 240 kg/ha NPK 15-15-15. Consequently, application of rhizobia and PSB improved soil fertility after harversting however using mixture of rhizobia and PSB inoculation plus 400 kg biofertilizer/ha +20 kg N/ha for soybean cultivation supported yield component, grain yield and oil, protein in seed than control and equivalent with treatment of chemical fertilizer (240 kg/ha NPK 15-15-15). This technique not only increased grain yield, incomes for farmers but also improved soil fertility.

Phosphate solubilizing bacteria (PSB) abundance and diversity were examined during two consecutive years, 2007 and 2008, in a crop/pasture rotation experiment in Uruguay. The study site comprised five treatments with different soil use intensity under a no-tillage regime. In the first year of sampling, abundance of PSB was significantly higher in natural prairie (NP) and permanent pasture (PP) than in continuous cropping (CC); rotation treatments harbored populations that did not differ significantly from those in the others. The percentage of PSB relative to total heterotrophic bacteria ranged between 0.18% and 13.13%. PSB diversity also showed statistical differences among treatments, with PP populations more diverse than those present in CC. In the second year sampled no differences were found in PSB abundance or diversity. Two hundred and fifty PSB were isolated in 2007 and classified according to their phosphate solubilization activity in vitro. Twelve of these isolates showing the greatest solubilization activity were selected for 16S rDNA sequencing. Ten isolates presumably belong to the genus Pseudomonas and two isolates showed high similarity with members of the genera Burkholderia and Acinetobacter.

The occurrence and distribution of phosphate solubilizing bacteria (PSB) capable of dissolving insoluble phosphates were investigated in this study in the sediments of river Ganga near the effluent discharge point of Kesoram Rayon Factory, Tribeni, West Bengal, India. A total of 20 bacterial isolates were screened. All isolates were tested for phosphate solubilizing activity on Pikovskaya's agar. Five different isolates exhibiting maximum formation of halos (zone of solubilization) around the bacterial colonies were selected for quantitative estimations of phosphate solubilization. Quantitative estimations for phosphate solubilization were analyzed for up to 5 days at an interval of 24h. Maximum solubilization of 144.36 µg P ml -1 was observed after 5 days of incubation in isolate RPSB6, while isolate RPSB8 showed minimum phosphate solubilization (121.76 µg P ml -1 ). The increase in solubilization coincided with the drop in pH. Many of these species showed wide range of tolerance to temperature. All isolates were tentatively identified as five different genera such as, Bacillus, Pseudomonas, Flavobacterium, Enterobacter and Aeromonas by morphological, physiological and biochemical tests. The presence of phosphate solubilizing bacteria and their ability to solubilize phosphate were indicative of the important role played by bacteria in the biogeochemical cycle of phosphorus and the plant growth in riverine ecosystems.

FULL PDF: https://ejar.journals.ekb.eg/article_172842.html Crop production is seriously threatened by drought. Greater availability of nitrogen and phosphorus through intercropping with grain legumes and inoculationwith Phosphate Solubilizing Bactaeria (PSB) can alleviate the negative effect of water stress on some crops. However, row crop-grain legume intercropping and using PSB bacteria is not welcomed or widely accepted by smallholder farmers in arid regions. The problem is that N-fixation by grain legumes cannot completely satisfy nitrogen demand of intercropped non-legume row crop especially in low phosphorus soils of these regions under restricted irrigation. The efficiency of PSB bacteria also is very low in the alkaline soil of this region. It suggests that some amount of nitrogen fertilizer should be used in this intercropping system. Nitrogen consumption also improves the efficiency of PSB bacteria. So, consumption of some mineral nitrogen, and incubation with PSB bacteria...

Thirty actinomycete strains were isolated from the rhizosphere of field-grown plants (Trifolium repens L.) and identified by microscopic characteristics, biochemical tests and molecular techniques. The 16S rDNA sequence analysis showed that most of the isolates belong to the Streptomyces genus. These thirty isolates were tested for their capabilities of solubilizing/mineralizing sparingly phosphate sources, N 2 -fixation and/or siderophore production, typical traits of the so-called Plant Growth Promoting Rhizobacteria (PGPR). Phosphate solubilizing ability was widely exhibited by the isolated. All of them produced acid phosphatase and thirteen of them alkaline phosphatase. Ten strains grew in N-free media. Almost all strains produced siderophores, however the production level was in general very low and only the strain Thermobifida MCR24 released considerable amounts of this metabolite. Streptomyces MCR9, Thermobifida MCR24 and Streptomyces MCR26 were selected to test their interactions with arbuscular mycorrhizal (AM) fungi because they produced the highest plant growth beneficial effects among ten isolates preselected as promissory PGPR. The inoculation of AM fungi improved early establishment of MCR9 in clover rhizosphere, and the late establishment of MCR24. The three actinomycete strains improved AM mycelial growth in absence of the test plant, and MCR9 and MCR26 also stimulate AM fungal spore germination. Inoculation of clover plants with either of the selected actinomycetes enhanced plant growth and N acquisition. Co-inoculation of actinomycetes and Glomus mosseae produced synergic benefits on plant growth and MCR9 and MCR24 also on P acquisition. The three selected actinomycetes improve AM formation by clover plants and Glomus mosseae.

Water samples from the river Ganga at Tribeni, West Bengal, India were sampled monthly to enumerate total heterotrophic bacteria (THB) and phosphate solubilizing bacteria (PSB) between January 2011 and December 2011. THB was high in the month of March and PSB was high in the month of July. The population density of THB ranged from 4.84-5.84x10 4 cells/ml and that of PSB ranged from 2.14-2.72x10 2 cells/ml. A significant variation in the capacity to solubilize phosphorous by the isolates of PSB were noted. The phosphatse activity of the isolates exhibited that the strain RPSB6 (27.38 µmoles/g/h) had higher activity followed by the strain RPSB9 (20.92 µmoles/g/h).

Broccoli (Brassica oleracea L. var. Italica) is an European vegetable and a considerably new introduction to Indian farmers [1, 2]. Biofertilizers can be used for broccoli cultivation as they play a very vital role in improving soil fertility [3-6]. There are several reports of Trichoderma and Pseudomonas mediated growth promotion and development of seedlings of several vegetable crops, namely cabbage, tomato, and capsicum [7-12]. Apart from improving nutritional status and growth of various vegetable crops also used as biocontrol agent against a wide range of soil borne fungal pathogens of crucifers [13]. The benefits of growth promoting microbes in vegetable crop production represent great opportunities for current agricultural practices [14]. A principal problem of organic farming is the low nutrient status of most organic fertilizers. This problem is further compounded by the difficulties in assessing the value of organic fertilizers through direct analysis of total quantities o...

This study was conducted with sugar beet in greenhouse and field at two soil type with different organic matter (containing 2.4 and 15.9% OM, referred as the low-and high-OM soil) conditions in order to investigate seed inoculation of sugar beet, with five N 2 -fixing and two phosphate solubilizing bacteria in comparison to control and mineral fertilizers (N and P) application. Three bacterial strains dissolved P; all bacterial strains fixed N 2 and significantly increased growth of sugar beet. In the greenhouse, inoculations with PGPR increased sugar beet root weight by 2.8-46.7% depending on the species. Leaf, root and sugar yield were increased by the bacterial inoculation by 15.5-20.8, 12.3-16.1, and 9.8-14.7%, respectively, in the experiment of low-and high-OM soil. Plant growth responses were variable and dependent on the inoculants strain, soil organic matter content, growing stage, harvest date and growth parameter evaluated. The effect of PGPR was greater at early growth stages than at the later. Effective Bacillus species, such as OSU-142, RC07 and M-13, Paenibacillus polymyxa RC05, Pseudomonas putida RC06 and Rhodobacter capsulatus RC04 may be used in organic and sustainable agriculture. q

CITATIONS 13 READS 120 4 authors, including: Some of the authors of this publication are also working on these related projects: e-PG pathshala for M. Sc.(Environmental Sciences) View project Comparative assessment of nutrients and heavy metals content during the composting and vermicomposting of OFMSW View project Neeraj Dilbaghi

The ability of a few soil microorganisms to convert insoluble forms of phosphorus to an accessible form is an important trait in plant growth-promoting bacteria for increasing plant yields. The use of phosphate solubilizing bacteria as inoculants increases the P uptake by plants. In this study, isolation, screening and characterization of 36 strains of phosphate solubilizing bacteria (PSB) from Central Taiwan were carried out. Mineral phosphate solubilizing (MPS) activities of all isolates were tested on tricalcium phosphate medium by analyzing the soluble-P content after 72 h of incubation at 30 8C. Identification and phylogenetic analysis of 36 isolates were carried out by 16S rDNA sequencing. Ten isolates belonged to genus Bacillus, nine to genus Rhodococcus, seven to genus Arthrobacter, six to genus Serratia and one each to genera Chryseobacterium, Delftia, Gordonia and Phyllobacterium. In addition, four strains namely, Arthrobacter ureafaciens, Phyllobacterium myrsinacearum, Rhodococcus erythropolis and Delftia sp. are being reported for the first time as phosphate solubilizing bacteria (PSB) after confirming their capacity to solubilize considerable amount of tricalcium phosphate in the medium by secreting organic acids. P-solubilizing activity of these strains was associated with the release of organic acids and a drop in the pH of the medium. HPLC analysis detected eight different kinds of organic acids, namely: citric acid, gluconic acid, lactic acid, succinic acid, propionic acid and three unknown organic acids from the cultures of these isolates. An inverse relationship between pH and P solubilized was apparent from this study. Identification and characterization of soil PSB for the effective plant growth-promotion broadens the spectrum of phosphate solubilizers available for field application. #

Available phosphorus is limiting in most cultivable soils in several parts of India, including Rajasthan. Four phosphate-solubilizing bacterial strains viz. Pseudomonas fluorescens BAM-4, Burkholderia cepacia BAM-6, B. cepacia BAM-12 and Aeromonas vaga BAM-77 were isolated from the rhizosphere of pearl millet (Pennisetum glaucum, cv. Raj 171), mung bean (Phaseolus aureus, cv. RMG 492) and sesame (Sesamum indicum, cv. RT 46). To the best of our knowledge, this is the first report on phosphate solubilization by Aeromonas vaga. Seed inoculation of mung bean with or without tricalcium phosphate (TCP) was performed to study the effect of single and dual bacterial inoculations in pot trials having sterilized sandy loam soil, and was found to enhance the growth and yield of plants. The results were on a par with chemical fertilizer, single superphosphate (SSP) and commercial biofertilizers, PSB (Bacillus polymyxa) and MC (Pseudomonas striata), used as standard reference. Addition of TCP to soil gave better results and dual inoculation was more effective than single inoculation of bacteria. Among the four strains studied, A. vaga and P. fluorescens were found to be more valuable as single inoculants in terms of plant growth, whereas in combination treatments, P. fluorescens along with B. cepacia and A. vaga performed very well both in the presence and absence of TCP.

The e ects of aldrin at rates 10 and 50 mg ml −1 on microbial function were studied under aerobic conditions. Parameters monitored included total culturable population of heterotrophic bacteria, number of culturable phosphate-solubilizing micro ora, number of bacteria which decompose protein with liberation of H2S, nitrifying bacteria, denitrifying bacteria and denitriÿcation activity. Culturable heterotrophic bacteria, phosphate-solubilizing bacteria, bacteria which decompose proteins with liberation of H2S and denitrifying bacteria were signiÿcantly increased at dose rates of 10 and 50 mg ml −1 of aldrin. However, the presence of aldrin decreased denitriÿcation activity at concentration of 50 mg ml −1 . Nitrifying population were not a ected as a consequence of the addition of aldrin, showing that these microorganisms can tolerate the concentrations of aldrin tested. ?

Pesticide residues contributing to the contamination of soil may influence microbial population of the soil and in turn fertility of soil. The present paper reports the effect of pesticides applied to soybean i.e. phorate, carbofuran, carbosulfan, thiomethoxam, imidacloprid, chlorpyriphos and monocrotophos on soil microflora. The viable count of rhizobia and phosphate solubilizing bacteria from rhizospheric soil of soybean ranged between 10 7 -10 8 cfu/g soil which was comparable to the count of bacteria from untreated (control) soil. No significant change in the total viable count of any kind of bacteria due to application of pesticides has been found showing their ability to degrade these pesticides.

Phosphate solubilizing bacteria (PSB) are known to be able to solubilize different forms of inorganic phosphates. A total of twenty four phosphate solublizing bacterial colonies were isolated on the Pikovskaya's (PKV) agar medium, containing insoluble tri-calcium phosphate (TCP), from the jute mill effluent exposed area of river Ganga at Bansberia, West Bengal, India.. The colonies showing clear halo zones around the bacterial growth were considered as phosphate solubilizers. Out of 24 bacterial isolates, 5 isolates showing highest phosphate solubilisation index (SI) ranged from 2.50-3.14 were selected for the further study as qualitative as well as quantitative estimation of phosphate. Among these 5 potent isolates, Bacillus sp JPSB16 showed the maximum phosphate solubilization index of 3.14 in Pikovskaya's agar plates along with highest soluble phosphate production of 203.64 μg P ml -1 in broth culture. Isolates JPSB15, JPSB17, JPSB18 and JPSB19 belong to genera Pseudomonas sp, Azotobacter sp, Flavobacterium sp and Bacillus sp as identified by their morphological, physiological and biochemical characteristics respectively. In all the phosphate solubilizing bacterial isolates, decrease in pH was observed in liquid medium ranging from 3.53 to 4.23 from initial pH of 7.0±0.2. The decrease in pH of the culture medium indicated the production of various organic acids by the culture.

Metal rich fly ash dumps may serve as repository of ecologically useful multi-functional rhizobacteria having potential use in the development of vegetation at the dumps. Therefore, in the present study bacteria from the rhizosphere of a wild perennial grass colonizing Indraprastha and Badarpur fly ash dumps of Delhi region were purified, identified and functionally characterized. The fly ash had low levels of nutrients, moisture and organic matter coupled with toxic levels of heavy metals (As, Cd, Cr, Cu, Hg, Ni, Pb and Zn). Both the dumps were mostly barren except for a few patches of Saccharum ravennae and some weedy species. Sixty five dominant, morphologically distinct rhizobacteria were purified, which belonged to 18 genera and 38 species. Gram-positive bacteria were dominating in the fly ash environment. Bacillus spp. and Paenibacillus spp. were common at both the dumps. Multi-metal tolerance was shown by diverse bacterial taxa. The minimum inhibitory concentration (MIC) was highest for As (12.5-20.0 mM) and Pb (7.5-10.0 mM), although many rhizobacteria also possessed significant tolerance to Cr, Zn, Ni, Cu, Co and Cd. The tolerance profiles of rhizobacteria to different metals may be ranked in the decreasing order as As > Pb > Cr > Zn > Ni > Cu > Co > Cd > Hg. Majority of rhizobacteria showed good siderophore activity. Multiple-metal tolerance was also coupled with high siderophore production in some of the isolates (Microbacterium barkeri IPSr74, Serratia marcescens IPSr90 and IPSr82, Enterococcus casseliflavus BPSr32, Bacillus sp. IPSr80, Pseudomonas aeruginosa BPSr43 and Brochothrix campestris BPSr3). Most of the bacteria could grow on nitrogen-deficient medium. However, the dominant nitrogenfixers reported from the rhizosphere of other Saccharum species were not detected. S. marcescens IPSr90 was the only rhizobacterium, which showed ACC-deaminase (ACCD) activity. Proportion of phosphatesolubilizing bacteria was high. Considerable improvement in the seedling establishment, plant weight and shoot length in rhizobacterial inoculated plants of S. ravennae in fly ash environment indicated the significance of rhizobacteria in its colonization and spread to the dumps. Representative rhizobacteria, with high MIC (for most of the metals) and good plant growth promoting (PGP) traits comparable to commercially useful bacterial inoculants were identified as S. marcescens IPSr82 and IPSr90, P. aeruginosa BPSr43, Paenibacillus larvae BPSr106, Arthrobacter ureafaciens BPSr55, Paenibacillus azotofixans BPSr107 and E. casseliflavus BPSr32. S. ravennae and some of these rhizobacteria may be potentially useful for the development of inoculation technologies for conversion of barren fly ash dumps into ecologically and economically productive habitats.

In the course of a project carried out in two regions of Spain, Castilla y León and Andalucía, aiming to find useful biofertilizers for staple grain-legumes, an efficient rhizobia nodulating chickpea (termed as C-2/2) and a powerful in vitro phosphate-solubilizing bacterial strain (termed as PS06) were isolated. Analyses of their 16S rDNA sequence indicated that they belong to the bacterial species Mesorhizobium ciceri and Pseudomonas jessenii, respectively. Greenhouse and field experiments were carried out in order to test the effect of single and dual inoculations on chickpea (ecotype ILC-482) growth. Under greenhouse conditions, plants inoculated with Mesorhizobium ciceri C-2/2 alone had the highest shoot dry weight. The inoculation treatment with P. jessenii PS06 yielded a shoot dry weight 14% greater than the uninoculated control treatment, but it was not correlated with shoot P contents. However, the co-inoculation of C-2/2 with PS06 resulted in a decrease in shoot dry weight with respect to the inoculation with C-2/2 alone. Under field conditions, plants inoculated with M. ciceri C-2/2, in single or dual inoculation, produced higher nodule fresh weight, nodule number and shoot N content than the other treatments. Inoculation with P. jessenii PS06 had no significant effect on plant growth. However, the co-inoculation treatment ranked the highest in seed yield (52% greater than the uninoculated control treatment) and nodule fresh weight. These data suggest that P. jessenii PS06 can act synergistically with M. ciceri C-2/2 in promoting chickpea growth. The contrasting results obtained between greenhouse and field experiments are discussed.

Recently, there has been a resurgence of interest in bioorganic fertilizers as part of sustainable agricultural practices to alleviate drawbacks of intensive farming practices. N2-fixing and P-solubilizing bacteria are important in plant nutrition increasing N and P uptake by the plants, and playing a significant role as plant growth-promoting rhizobacteria in the biofertilization of crops. A study was conducted in order to investigate the effects of two N2-fixing (OSU-140 and OSU-142) and a strain of P-solubilizing bacteria (M-13) in single, dual and three strains combinations on sugar beet and barley yields under field conditions in 2001 and 2002. The treatments included: (1) Control (no inoculation and fertilizer), (2) Bacillus OSU-140, (3) Bacillus OSU-142, (4) Bacillus M-13, (5) OSU-140 + OSU-142, (6) OSU-140 + M-13, (7) OSU-142 + M-13, (8) OSU-140 + OSU-142 + M-13, (9) N, (10) NP. N and NP plots were fertilized with 120 kg N ha−1 and 120 kg N ha−1 + 90 kg P ha- for sugar beet and 80 kg N ha−1 and 80 kg N ha−1 + 60 kg P ha−1 for barley. The experiments were conducted in a randomized block design with five replicates. All inoculations and fertilizer applications significantly increased leaf, root and sugar yield of sugar beet and grain and biomass yields of barley over the control. Single inoculations with N2-fixing bacteria increased sugar beet root and barley yields by 5.6–11.0% depending on the species while P-solubilizing bacteria alone gave yield increases by 5.5–7.5% compared to control. Dual inoculation and mixture of three bacteria gave increases by 7.7–12.7% over control as compared with 20.7–25.9% yield increases by NP application. Mixture of all three strains, dual inoculation of N2-fixing OSU-142 and P-solubilizing M-13, and/or dual inoculation N2-fixing bacteria significantly increased root and sugar yields of sugar beet, compared with single inoculations with OSU-140 or M-13. Dual inoculation of N2-fixing Bacillus OSU-140 and OSU-142, and/or mixed inoculations with three bacteria significantly increased grain yield of barley compared with single inoculations of OSU-142 and M-13. In contrast with other combinations, dual inoculation of N2-fixing OSU-140 and P-solubilizing M-13 did not always significantly increase leaf, root and sugar yield of sugar beet, grain and biomass yield of barley compared to single applications both with N2-fixing bacteria. The beneficial effects of the bacteria on plant growth varied significantly depending on environmental conditions, bacterial strains, and plant and soil conditions.

Aim: To determine the cold tolerance and plant growth promotion potential of Serratia marcescens strain SRM (MTCC 8708). Methods and Results: Serratia marcescens strain SRM was isolated from the flowers of summer squash plants, showing no apparent symptoms of yellow vine disease. It was evaluated for growth and plant growth promotion attributes at 15 and 4°C. At 15°C, the isolate was able to solubilize 76AE6 lg ml )1 of P and produce Indole Acetic Acid, IAA (11AE1 lg ml )1 ). HCN and siderophore production were also detected at 15°C. The isolate retained all the plant growth promotion traits at 4°C. Seed bacterization with the isolate significantly enhanced plant biomass and nutrient uptake of wheat seedlings grown in cold temperatures. Conclusion: Serratia marcescens strain SRM is a promising cold-tolerant isolate that can significantly influence wheat seedling growth at cold temperatures. Significance and Impact of the Study: This strain can be employed as a bioinoculant in cold temperature conditions.

An experiment was carried out to isolate, screen and characterize bacteria collected from an industrially polluted site of Bhaluka under the Mymensingh district and to evaluate their phosphorus (P) solubilizing capacity. About ten plant and soil samples from six different spots were collected from the site. Thirty four bacterial isolates were screened and pure cultures of the different bacterial isolates were prepared. Among the bacterial isolates 25 were gram negative and 9 were gram positive. About 31 bacterial isolates had catalase producing capacity and remaining 3 were negative to catalase test. Bacterial isolates were grown on a NBRIP media to determine their phosphorus solubilizing capacity. About 25 bacterial isolates were shown P solubilizing capacity. Isolate SB8 gave the highest result about 11.42 PSI (phosphorus solubilizing index), whereas other bacterial isolates showed moderate P solubilizing capacity (PSI 1.75-6.35). A plant trial with selected isolates (SB8, SB15, SB25) were also done and SB8 achieved 10% higher P content in comparison with control which supports the in vitro P solubilization assays. To cite this article: Shahinur MR, QF Quadir, A Rahman, MN Asha and MAK Chowdhury, 2014. Screening and characterization of phosphorus solubilizing bacteria and their effect on rice seedlings. Res. Agric., Livest. Fish. 1(1): 27-35. Shahinur et al.

A pot experiment was conducted in the green house to investigate the establishment of phosphate solubilizing strains of Azotobacter chroococcum, including soil isolates and their mutants, in the rhizosphere and their effect on growth parameters and root biomass of three genetically divergent wheat cultivars (Triticum aestivum L.). Five fertilizer treatments were performed: Control, 90 kg N ha -1 , 90 kg N + 60 kg P 2 O 5 ha -1 , 120 kg N ha -1 and 120 kg N + 60 kg P 2 O 5 ha -1 . Phosphate solubilizing and phytohormone producing parent soil isolates and mutant strains of A. chroococcum were isolated and selected by an enrichment method. In vitro phosphate solubilization and growth hormone production by mutant strains was increased compared with soil isolates. Seed inoculation of wheat varieties with P solubilizing and phytohormone producing A. chroococcum showed better response compared with controls. Mutant strains of A. chroococcum showed higher increase in grain (12.6%) and straw (11.4%) yield over control and their survival (12-14%) in the rhizosphere as compared to their parent soil isolate (P4). Mutant strain M37 performed better in all three varieties in terms of increase in grain yield (14.0%) and root biomass (11.4%) over control.

Within rhizobia, two species nodulating chickpea, Mesorhizobium ciceri and Mesorhizobium mediterraneum, are known as good phosphate solubilizers. For this reason, we have analysed the ability to solubilize phosphate of a wide number of strains isolated from Cicer arietinum growing in several soils in Spain. The aim of this work was to analyse microbial populations nodulating chickpea, that are able to solubilize phosphates, using molecular techniques. In the present work we analyzed 19 strains isolated from effective nodules of C. arietinum growing in three soils from the North of Spain. Nineteen strains showed ability to solubilize phosphate in YED-P medium. These strains were separated into 4 groups according to the results obtained by 879F-RAPD fingerprinting. The 16S rDNA sequencing of a representative strain from each group allowed the identification of strains as belonging to the genus Mesorhizobium. Strains from groups I and II showed a 99.4% and 99.2% similarity with M. mediterraneum UPM-CA142 T , respectively. The strains from group III were related to M. tianshanense USDA 3592 T at a 99.4% similarity level. Finally, the strain from group IV was related to M. ciceri USDA 3383 T with a 99.3% similarity. The LMW RNA profiles confirmed these results. Strains from groups I and II showed an identical LMW RNA profile to that of M. mediterraneum UPM-CA142 T ; the profile of strains from group III was identical to that of M. tianshanense USDA 3592 T and the profile of strains from group IV was identical to that of M. ciceri USDA 3383 T . Different 879F-RAPD patterns were obtained for strains of the group I, group II and the M. mediterraneum type strain (UPM-CA142 T ). The 879-RAPD patterns obtained for group III also differed from the pattern shown by M. tianshanense USDA 3592 T . Finally, the patterns between group IV and M. ciceri USDA 3383 T were also different. These results suggest that groups I and II may be subspecies of M. mediterraneum, group III a subspecies of M. tianshanense and group IV a subspecies of M. ciceri. Nevertheless, more studies are needed to establish the taxonomic status of strains isolated in this study.

Phosphate-solubilizing microorganisms are often used as plant growth promoters. In the frame of a project focused on the isolation of endosymbionts and ectorhizospheric bacteria associated with Phaseolus vulgaris plants growing in a mountain soil at the north-east of Portugal, we obtained six bacterial strains with high phosphate-solubilizing capability, as demonstrated by the formation of ‘halos’ when plated in YED medium

Abstract

Phosphate solubilization and growth promotion by Pseudomonas fragi CS11RH1 (MTCC 8984), a psychrotolerant bacterium isolated from a high altitude garlic rhizosphere from the Indian Himalayas, are reported here. The identity of the isolate was arrived on the basis of its biochemical features and sequencing of the 16S rRNA gene. The isolate grew and solubilized phosphate at temperatures ranging from 4 to 30°C. Besides solubilizing P it produced indole acetic acid (IAA) and hydrogen cyanide (HCN). Seed bacterization with the isolate significantly increased the percent germination, rate of germination, plant biomass and nutrient uptake of wheat seedlings. While Pseudomonas fragi is normally associated with the spoilage of dairy products stored at cold temperatures, this is an early report on the plant growth promoting ability of the bacterium.

Key words psychrotolerant - Pseudomonas fragi - phosphate solubilization - plant growth promotion

The growth of phosphate solubilizing bacteria (PSB) was examined inresponse to pond fertilization with poultry dropping (PD) (12,500 kgha-1 y-1), cattle manure (CM) (25,000 kg ha-1 y-1), inorganic fertilizer (IF) consisting of urea (10.83 kg ha-1 y-1) and single super phosphate (43.52 kg ha-1 y-1) and inorganic-organic mixed fertilizers (PD:CM:IF - 1:1:1) in simulated fish ponds under alluvial and laterite

The field experiments were conducted at the Indian Agricultural Research Institute, New Delhi, India for 3 years from 2001-2002 to 2003-2004 to study the relative efficiency of diammonium phosphate (DAP) and Mussoorie rock phosphate along with phosphorus solubilizing bacteria inoculation (MRP ? PSB) at different rates of application on productivity and phosphorus balance in a ricerapeseed-mungbean cropping system. Phosphorus application significantly increased the productivity of rice-rapeseed-mungbean cropping system and resulted in an increase in 0.5 M NaHCO 3 extractable P content in soil. The relative agronomic effectiveness (RAE) of MRP ? PSB in relation to DAP as judged by the total productivity was 53-65% in the first cycle but reached 69-106% in the third cycle of the cropping system. The P balance (applicationcrop removal) was generally more positive for MRP ? PSB than DAP and the highest P balance was recorded with an application of 52.5 kg P ha -1 as MRP ? PSB, resulted in highest 0.5 M NaHCO 3 extractable P content in soil. The present study, thus, shows that MRP ? PSB could be usefully employed as an alternative to DAP in long term in the ricerapeseed-mungbean cropping system.

Seventy one bacteria associated with dipterocarp seedlings and saplings were isolated from peat soil at Nyaru Menteng Arboretum and Palangkaraya University Nursery, Central Kalimantan, Indonesia. These bacteria were screened for their capacity in solubilizing inorganic and mineralizing organic phosphate using modified NBRIP media in vitro. Most isolates were able to solubilize Ca 3 (PO 4 ) 2 with various solubilization index in the first screening. Secondary screening using P sources with lower pH, further grouped these bacteria into: (1) solubilizing inorganic Ca 3 (PO 4 ) 2 with pH 4.5: Erwinia sp. CK10, Roseateles sp. CK15, Rhizobium sp. CK19, Enterobacter sp. CK23, and Erwinia sp. CK24.; (2) mineralizing organic C 6 H 6 (OPO 3 H 2 ) 6 with pH 6.0: Roseateles sp. CK15, Rhizobium sp. CK19, Enterobacter sp. 23CK, Erwinia sp. CK24, NI CK53, and NI CK54;