1. bookVolume 72 (2021): Edition 2 (June 2021)
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Lantana charcoal as potent carrier material for Azotobacter chroococcum

Publié en ligne: 09 May 2022
Volume & Edition: Volume 72 (2021) - Edition 2 (June 2021)
Pages: 83 - 91
Reçu: 17 Jun 2021
Accepté: 16 Aug 2021
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License
Format
Magazine
eISSN
2719-5430
Première parution
30 Mar 2016
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4 fois par an
Langues
Anglais
Abstract

Azotobacter chroococcum is a universally accepted plant growth-promoting rhizospheric bacterium, which, as a biofertilizer, helps to increase the nitrogen level, solubilize the unavailable form of phosphorus, ensure growth-promoting metabolites, and control pathogenic microbes in the soil. A good strain of plant growth-promoting rhizobacteria (PGPR) needs to be produced, formulated, transported, stored, and distributed to the agriculture field. During all these operations, bacterial inoculants are transferred via a carrier material. One of the important challenges in biofertilizer technology is to ensure stability of the bacteria in the carrier. The study aimed to assess a novel carrier Lantana charcoal (LC; obtained from Lantana camara biomass), as compared to some currently available carriers. LC exhibited higher carbon content, low N2 content, neutral pH, and, above all, higher water-holding capacity, making it a suitable carrier material for A. chroococcum and possibly other PGPR. As a carrier, it showed no contamination during storage, exhibited the highest moisture content and moderate culture holding coefficient, and supported the highest colony-forming units per gram at the end of the storage period. Thus, LC cannot only serve as a better carrier, but its large-scale application would also ensure a reasonable use of this weed.

Keywords

Schlagwörter

Introduction

Azotobacter is a universally accepted broad-spectrum plant growth-promoting rhizobacterium (PGPR) showing both nitrogen-fixing and phosphate-solubilizing characteristics (Mrkovac et al., 1996; Kumar and Singh, 2001). Its various species do secrete different growth substances like auxin, cytokinins, and gibberellins (Salmeron et al., 1990; Gonzales Lopez et al., 1991). Because of these features, Azotobacter has beneficial effects on plant growth and yield (Idris, 2003). Among various species of this PGPR, Azotobacter chroococcum is the most studied one (Wani et al., 2016).

Biofertilizer technology requires commercial production of PGPR and its subsequent delivery to agricultural fields through various stages of operations such as formulation, transportation, storage, and distribution. During these operations, the biological activity of PGPR may be reduced rapidly if an incorrect carrier is chosen or inappropriate handling or storage is done. The choice of carrier material is thus an important factor that protects the bacteria during transportation and storage and keeps the number of viable count to a maximum (El-Fattah et al., 2013; Arora et al., 2014).

Peat has been demonstrated to be the most widely used carrier (Burton, 1967; Peterson and Lovnachan, 1981), but it is not available everywhere (Tilak and Rao, 1978). Other known carrier materials tested for the formulation of the biofertilizers are alginate, lignite, cellulose powder, sawdust, organic waste, coal, perlite, and agro-industrial waste. Most of them are, however, not suitable for commercial production as they are costly (Brockwell and Bottomley, 1995; Stephens and Rask, 2000; El-Fattah et al., 2013). Agro-residues based biochar has also been proposed as a candidate carrier (Lehman, 2007; Ghazi, 2017), but there is global preference for the application of agro-residues in bioethanol production (Talebnia et al., 2010; Sahay, 2020).

Lantana camara, belonging to the angiosperm family Verbenaceae, is a weed found in many countries, especially in India, South Africa, and Australia, occupying millions of hectares of land. The weed grows rapidly suppressing the native plant species. Because of its obnoxious and invasive nature and allelopathic effect on cultivated plants (Negi et al., 2019) and also owing to the presence of a higher concentration of fermentation inhibitory compounds in it, it can be hardly a sustainable source of biomass for various applications including bioethanol production. One of the possible ways to use it is by converting the biomass into charcoal for various purposes (Sharma et al., 1988; Bhagwat et al., 2012). Therefore, the objective of this work was to assess the suitability of charcoal obtained from Lantana biomass (LC) as a carrier for A. chroococcum.

Materials and methods
Procurement of PGPR

Rhizobacterium A. chroococcum (NCIM No. 5576) was procured from National Collection of Industrial Micro-organism (NCIM), National Chemical laboratory, Pune, India. The culture was maintained on Jensen medium at 30°C for further study.

Assaying plant growth-promoting activities

The nitrogen fixation ability of bacteria was tested by applying the semimicro-Kjeldahl method (Bremner, 1965). The nitrogen fixation efficiency (NFE) was determined in terms of total nitrogen fixed per milligram sucrose consumption.

The phosphate-solubilizing efficiency was examined by the method of Pikovskaya (1948) and by determining the phosphate-solubilizing index (PSI) (Premono et al., 1996) according to the following formula: PSI=colonydiameter+halozonediametercolonydiameter {\rm{PSI}} = {{{\rm{colony}}\,{\rm{diameter} + \rm{halo}}\,{\rm{zone}}\,{\rm{diameter}}} \over {{\rm{colony}}\,{\rm{diameter}}}}

The siderophore-producing ability was estimated according to the universal chrome azurol sulfonate (CAS) assay method (Schwyn and Neilands, 1987). Briefly, CAS-hexadecyltrimethyl ammonium bromide (CAS-HDTMA) solution was prepared by mixing 120 ml of CAS solution (0.121 g of CAS dissolved in100 ml of distilled water with the addition of 20 ml of 1 mM FeCl3.6H2O solution) and 29 ml of HDTMA solution (0.729 g of HDTMA dissolved in 400 ml of distilled water). Then, CAS agar was prepared by adding 100 ml of CAS-HDTMA solution slowly to 900 ml of sterilized Jensen medium. The spot-inoculated bacterial colonies on CAS agar plate showing orange to red haloes were considered siderophore-positive ones.

Quantitative estimation of siderophores was carried out by the method described earlier (Pyne, 1994), and percent siderophore units (PSU) were calculated using the following formula: PSU=(ArAs)Ar×100 {\rm{PSU}} = {{\left( {{{\rm{A}}_{\rm{r}}} - {{\rm{A}}_{\rm{s}}}} \right)} \over {{{\rm{A}}_{\rm{r}}}}} \times 100 where Ar = absorbance of reference at 630 nm (CAS reagent) and As = absorbance of sample at 630 nm.

Mass production of broth

Multiplication of the bacterium was carried out in Jensen (nitrogen-free) medium containing (g/l): sucrose 20.0, dipotassium phosphate 1.0, magnesium sulfate 0.50, sodium chloride 0.50, ferrous sulfate 0.10, sodium molybdate 0.005, calcium carbonate 2.0, and agar 20.0; pH 7.2 (Jensen, 1951) in ambient orbital incubator shaker at 150 rpm. Flasks containing 250 ml of the medium were inoculated with 2.5 ml of active mother culture of A. chroococcum and incubated for 4–5 d at 30°C. Broth with about 109 colony forming unit (CFU) per ml thus obtained was used to inoculate the carrier material.

Preparation of LC

L. camara biomass was obtained from locally available dried wild plants. Exactly 30 kg of sun-dried biomass (stems and branches) of L. camara was used to obtain LC. It was anaerobically processed in a 300-kg pyrolysis kiln developed by the Central Institute of Agricultural Engineering (CIAE), Bhopal to obtain the LC. The successive steps were as follows:

L. camara biomass (stems and branches) was collected.

The adhered soil particles were cleared and the biomass was sun-dried.

The dried materials were pyrolyzed at 300°C in a kiln for 2h under anaerobic condition.

LC was crushed with a crusher into 100 mesh size.

LC powder was autoclaved at 121°C for 15 min followed by drying at 80°C in the oven for 24 h.

Dried LC was packed in a plastic bag under sterile conditions.

Sources of other carrier materials and their chemical properties

Other carrier materials were obtained from different sources as follows: wood charcoal (WC) (locally available), lignite (S & S Biotech, Nagpur, India), vermicompost (VC) (SonaVermicompost, Mandideep, India), and farmyard manure (FYM) (farm of MPVS, Bhopal, India). The carrier materials were analyzed for their chemical properties including total nitrogen estimation by the semi-Kjeldahl method of Bremner (1965) and pH and electrical conductivity (EC) (S/m) by the standard methods of Peech (1965).

Loading of bacterial culture onto the carriers

All the carrier materials were air-dried, ground, and passed through a 100-meshscreen. Their pH was adjusted to neutrality with calcium carbonate solution and they were sterilized by autoclaving at 121°C for 15 min. Log phase culture of bacteria (CFU:108–109 per ml) was mixed with the carrier materials according to their water-holding capacity in aseptic condition (Table 1). Carriers containing culture were filled in sterile polyethylene bags leaving one-third space as void, sealed immediately, and stored at 4°C. Each treatment was carried out in two sets of three each (triplicates), one set for monthly viability assay and another set for assaying viability in 6months. From the first set, 1 g of sample was taken out at 1-month intervals, while the last sample was taken out from the second set after 6 months, so that the impact of perturbation that the first set suffered during sampling could be assessed.

Inoculated carrier materials containing various volumes of bacterial liquid culture and amounts of carrier materials

Tabelle 1. Inokulierte Trägermaterialien, die verschiedene Volumina an bakterieller Flüssigkultur und Mengen an Trägermaterialien

Carrier materials Carrier material (g) Liquid culture (ml) Inoculated carrier materials (g)
LC 100 205 305
WC 125 176 301
LN 174 127 301
VC 174 126 300
FYM 173 130 303
Viable count of bacterium

Samples were taken out aseptically at 1-month intervals for the calculation of viability of inoculated bacteria. One gram of sample for each treatment was mixed in 9 ml of sterile distilled water and shaken at 120 rpm for 1 min to facilitate separation of bacteria from the carrier. The bacterial suspension was serially diluted to achieve 10-fold dilution (10−10). Aseptically withdrawn aliquot of 100 μl from each 10−6 dilution was spread onto nitrogen-free agar medium with three replicates. All plates were incubated at 30°C for 2 d; after that, the colonies formed were counted and the results were expressed in CFU per gram.

Water-holding capacity and moisture retention of carrier

The water-holding capacity of carriers was measured for 10 g of a selected carrier according to the method applied for soil (Sumner, 1999). For the analysis of moisture retention attribute, 40 g of carrier materials pre-saturated with water was divided into four parts of 10 g each. The first part was kept in a hot air oven for 6 h at 160°C, then cooled down at room temperature for an hour and weighed to find the moisture content (x1). The other three parts were kept for 6 months (at 4°C) and then oven-dried, cooled, and weighed (x2) as previously. Moisture (water) held (retention) was derived by subtracting x1−x2 and the data were then used to obtain the values in percentage.

Culture holding coefficient

Culture holding coefficient (CHO), that is, CFU per gram on 0 d/water-holding capacity, was calculated for each carrier material by the formula: CHO=CFUi(x1x)×100 {\rm{CHO}} = {{{\rm{CF}}{{\rm{U}}^{\rm{i}}}} \over {\left( {{{\rm{x}}_1} - {\rm{x}}} \right) \times 100}} where CFUi is CFU in x g of the carrier material and x1 is the weight of x g of the carrier material saturated with water.

Statistical analysis

The experiments were conducted in triplicate and three times. Statistical data were analyzed using analysis of variance (ANOVA; Tukey's multiple comparisons test) in GraphPad Prism 9 software. Standard errors were determined for all mean values, and differences at the p ≤ 0.05 level were considered significant. Post-hoc least significant differences (LSD) test was also conducted at 5% (p ≤ 0.05) probability level (Williams and Abdi, 2010).

Results and discussion
Recovery of charcoal from L. camara biomass

Thirty kilograms of the sun-dried L. camara biomass yielded 9.4 ± 1.07 kg of charcoal, showing carbonization efficiency (%) of 31.33 ± 1.07. The yield and efficiency were similar to an earlier finding (Abebe, 2017).

Chemical properties of different carrier materials

LC showed lower N2, lower inherent moisture content, higher carbon content, and nearly neutral pH, as compared to other selected carriers (Table 2). In order to improve and promote biofertilizer technology, quality control initiatives with certain minimum specifications for marketable biofertilizers have been introduced. Thus, carrier materials used to carry the biofertilizer should have higher carbon content and neutral pH (Yadav and Chandra, 2014); both of these are shown by LC.

Chemical properties of the selected carrier materials

Tabelle 2. Chemische Eigenschaften ausgewählter Trägermaterialien

Carrier material N(%) OC(%) pH EC(S/m) Moisture (%) References
LC 0.78 58.60 7.36 597 5.90 Abebe et al., 2017
WC 0.72 49.50 7.01 512 7.20 Sudhakar et al., 2004
Lignite 0.86 29.30 6.58 642 9.80 Rumpel et al., 1998
VC 1.01 25.90 7.10 370 17.58 Packialakshmi and Aliya, 2014; Ravimycin, 2016
FYM 1.83 51.80 6.80 330 15.74 Ravimycin, 2016
Water-holding and retention attributes of carriers

Water absorbed and held by LC was the highest, followed by WC, lignite, VC, and FYM (Table 3). The order of water retention percentage of carriers was FYM < lignite < VC < LC < WC. The water-holding capacity showed an inverse relation with the bulk density of the carrier materials. Thus, LC with the lowest bulk density showed the highest water-holding capacity. The same reason seems to hold in the case of the moisture loss process, as LC and WC also exhibited the lowest moisture retention attribute. LC showed the lowest water retention attribute, yet it showed a higher total amount of moisture held in it at the end of the storage period. The higher water-holding capacity seems to nullify the negative effect of low retention attribute. The highest water-holding capacity of LC enables it to take up and carry a higher volume of inoculum.

Water absorption (holding), retention (% held), and loss (% in 6 months) of different carrier materials

Tabelle 3. Wasseraufnahme (Halten), Retention (% gehalten) und Verlust (% in 6 Monaten) verschiedener Trägermaterialien

Carrier material Water absorbed (ml) Water held (%) Moisture lost (%)
At the start After 6 months
LC 20.56 ± 0.13e 205.6 ± 1.38e 93.13 ± 2.73e 54.71 ± 1.02e
WC 14.08 ± 0.20d 140.86 ± 2.33d 64.86 ± 2.31d 53.87 ± 2.38d
Lignite 7.35 ± 0.11b 73.56 ± 1.15b 44.83 ± 2.84b 38.90 ± 4.83b
VC 7.26 ± 0.13a 72.6 ± 1.24a 41.10 ± 1.61a 43.48 ± 2.65c
FYM 7.53 ± 0.19c 75.3 ± 1.90c 51.33 ± 2.52c 31.86 ± 2.26a
LSD (0.05) 0.39 3.91 6.26 7.49

Values are the means ± SE. Values within the same column followed by different superscript letters are significantly different at the p ≤ 0.05 level.

Viable count in carrier

All the selected carrier materials were sterilized at the outset and found uncontaminated during 6 months of the incubation period. In as a similar experiment reported earlier, Rhizobium spp.-inoculated carrier (peat) showed no contamination after 6 months of incubation (Somasegaran and Hallyday, 1982). Of the selected carrier materials studied to determine their impact on the viability of bacteria after 6 months of inoculation, LC was the most effective one maintaining the cell density at a higher level (Table 4). Of course, the initial higher viable count of LC was due to its highest water-holding capacity. In the first month, bacterial density was found to increase invariably in all the carrier materials possibly due to the presence of residual nutrients. The population of bacterium then started declining in all the carriers. The decline was, however, the least in LC. Thus, an optimum cell viable count (8.33 × 107 CFU) was obtained at the end of the storage period (Table 4). The impact of PGPR inoculation on plant growth and productivity depends a lot on the number of bacteria introduced into the soil (Duquenne, 1999).

PGPR (Azotobacter chroococcum 5576) survivability shown as CFU in various carriers as a function of time (days) at room temperature

Tabelle 4. Überlebensfähigkeit von PGPR (A. chroococcum 5576) gezeigt als CFU in verschiedenen Trägermaterialien als Funktion der Zeit (Tage) bei Raumtemperatur

Carrier materials PGPR CFU (× 107 per g) as obtained after various periods of storage (d)

0 30 60 90 120 150 180
LC 77 ± 8.19e 147.3 ± 2.30e 104.3 ± 6.00e 98.33 ± 9.49e 77.66 ± 7.83e 27.00 ± 2.08e 8.33 ± 1.20e
WC 70.5 ± 3.48d 90.66 ± 6.64d 64.33 ± 5.60d 32.00 ± 4.04d 18.00 ± 1.73d 10.66 ± 1.20d 3.33 ± 0.33d
LN 53.5 ± 2.33c 82.33 ± 2.96c 35.66 ± 2.02c 31.66 ± 2.18c 22.66 ± 2.02c 9.33 ± 0.88c 2.66 ± 0.33c
VC 33.5 ± 2.60a 46.66 ± 2.90a 23.33 ± 1.76a 16.33 ± 1.45a 10.66 ± 0.88a 1.66 ± 0.66a 0.34 ± 0.04a
FYM 47.5 ± 2.02b 56.66 ± 3.48b 21.33 ± 1.20b 17.66 ± 0.88b 08.33 ± 0.88b 1.00 ± 0.57b 0.14 ± 0.02b

Values are the means ± SE. Values within the same column followed by different superscript letters are significantly different at the p ≤ 0.05 level.

Therefore, higher bacterial survivability in the carrier material is important to achieve sufficient bacterial density in the soil following application (Feng et al., 2002; Arora et al., 2014). The highest organic carbon (OC) and moisture content of LC as compared to the other carrier materials (Table 2) seem to help the bacterial cells to remain viable during storage.

Culture holding coefficient

CHO was determined for all the carrier materials to examine the contribution of their material quality to the effectivity as carrier materials and to nullify the exaggeration effect of bulk density. CHO of lignite was found to be the best one and that of LC was only better than WC (Table 5), indicating a dual trend. While in general, bulk density (lignite > VC ≈ FYM > WC ≈ LC) has an inverse relation with CHO (WC > LC > VC > FYM > lignite), material characteristics do play some role. Thus, FYM and VC or LC and WC have almost similar bulk densities, but exhibit different CHOs. LC with lower bulk density and higher water-holding capacity has, in addition, suitable material characteristics, proving it a better carrier material.

Culture holding coefficients of the selected carrier materials

Tabelle 5. Kulturhaltekoeffizient ausgewählter Trägermaterialien

Carrier materials LC WC Lignite VC FYM
CHO 4.69 4.36 6.70 5.50 6.50

CHO, culture holding coefficient

Testing LC as a carrier against the set standards

There are certain standards set for the carrier materials with respect to their physico-chemical properties and performance (Table 6). Physico-chemical data as well as results obtained from the experiment regarding LC's ability to support inoculated A. chroococcum were compared with the standards; LC fulfilled these requirements, and thus proved as a potential carrier for A. chroococcum and possibly for other microbes as well.

Standards for the preparation of carrier for Azotobacter biofertilizer

Tabelle 6. Standards für die Herstellung von Trägern für Azotobacter-Biodünger

Parameters Standard References
Base material Solid (moist/dry or granules form) or liquid based BIS, 1985, Bhattacharjee, 2014;Yadav and Chandra, 2014
Viable cell count 5 × 107/g of carrier (CFU).Biofertilizer or 1 × 108 / ml of liquid base Singh, 2015; BIS, 1985; Yadav and Chandra, 2014
pH value 6.5–7.5 BIS, 1985; Yadav and Chandra, 2014
Moisture % By weight, 30%–40% for the carrier material BIS, 1985; Yadav and Chandra, 2014
Water retention High water-holding capacity BIS, 1985; Yadav and Chandra, 2014
Partial size Passable through 100 meshsieves BIS, 1985; Yadav and Chandra, 2014
Contamination level None at 10−5 dilution BIS, 1985; Yadav and Chandra, 2014
Strain selection Strain capable of fixing N2 at least10 mg/g of sucrose consumed BIS, 1985; Yadav and Chandra, 2014

An ideal carrier material should be easily available, low cost, non-toxic, sterilizable, mixable, and packageable. LC got through these tests. Additionally, a carrier should have readily adjustable pH, high OC content and water-holding capacity, and the ability to allow gas exchange, particularly oxygen (Somasegaran, 1994; Stephens and Rask, 2000; Rebah, 2002; Ferreira, 2005). LC, as shown above, is not inferior to the selected carrier materials (Table 6). Moreover, the carrier must also exhibit characteristics such as tolerance to harsh environmental conditions, eco-friendliness, cost-effectiveness, and solubility in water, so that bacteria can be released easily (FAO, 1993). LC displays many of these attributes, and thus has the potential to serve as a carrier for A. chroococcum and possibly other PGPR.

Assaying plant growth-promoting activities before and after storage

Selected plant growth-promoting activities of A. chroococcum 5576 before [performance (i)] and after 6 months of the storage period [performance (f)] are shown in Table 7. The bacterium recovered from the carrier exhibited almost the same level of activity for each attribute (NFE, PSI, or PSU) as before storage. This indicates that LC as a carrier does not contain any chemical that is inhibitory to the bacterium and can permit microbes to survive during storage to the maximum extent.

Performance of Azotobacter chroococcum 5576 regarding plant growth-promoting traits before (i) and after (f) storage period in the carrier LC

Tabelle 7. Leistung von A. chroococcum 5576 hinsichtlich der pflanzenwachstumsfördernden Merkmale vor (i) und nach (f) Lagerzeit in der Träger-L-Holzkohle

Plant growth-promoting parameters Performance (i) Performance (f)
NFE (mg per g sucrose consumed) 12.46 ± 0.35 12.45 ± 0.40
PSI 03.90 ± 0.10 03.34 ± 0.09
PSU 42.75 ± 0.78 42.80 ± 0.57

Values are the mean of three replications ± SE. NFE, N2 fixation efficiency; PSI, phosphate-solubilizing index; PSU, percent siderophore production

Conclusion

The weed L. camara yielded LC with important attributes such as higher carbon content, low N2 content, neutral pH, moderate water retention attribute, and, above all, higher water-holding capacity, making it a suitable material to serve as a carrier for A. chroococcum and possibly other PGPR. Its large-scale commercial application would also help to control the population of this aggressive invader.

Standards for the preparation of carrier for Azotobacter biofertilizerTabelle 6. Standards für die Herstellung von Trägern für Azotobacter-Biodünger

Parameters Standard References
Base material Solid (moist/dry or granules form) or liquid based BIS, 1985, Bhattacharjee, 2014;Yadav and Chandra, 2014
Viable cell count 5 × 107/g of carrier (CFU).Biofertilizer or 1 × 108 / ml of liquid base Singh, 2015; BIS, 1985; Yadav and Chandra, 2014
pH value 6.5–7.5 BIS, 1985; Yadav and Chandra, 2014
Moisture % By weight, 30%–40% for the carrier material BIS, 1985; Yadav and Chandra, 2014
Water retention High water-holding capacity BIS, 1985; Yadav and Chandra, 2014
Partial size Passable through 100 meshsieves BIS, 1985; Yadav and Chandra, 2014
Contamination level None at 10−5 dilution BIS, 1985; Yadav and Chandra, 2014
Strain selection Strain capable of fixing N2 at least10 mg/g of sucrose consumed BIS, 1985; Yadav and Chandra, 2014

Inoculated carrier materials containing various volumes of bacterial liquid culture and amounts of carrier materialsTabelle 1. Inokulierte Trägermaterialien, die verschiedene Volumina an bakterieller Flüssigkultur und Mengen an Trägermaterialien

Carrier materials Carrier material (g) Liquid culture (ml) Inoculated carrier materials (g)
LC 100 205 305
WC 125 176 301
LN 174 127 301
VC 174 126 300
FYM 173 130 303

Performance of Azotobacter chroococcum 5576 regarding plant growth-promoting traits before (i) and after (f) storage period in the carrier LCTabelle 7. Leistung von A. chroococcum 5576 hinsichtlich der pflanzenwachstumsfördernden Merkmale vor (i) und nach (f) Lagerzeit in der Träger-L-Holzkohle

Plant growth-promoting parameters Performance (i) Performance (f)
NFE (mg per g sucrose consumed) 12.46 ± 0.35 12.45 ± 0.40
PSI 03.90 ± 0.10 03.34 ± 0.09
PSU 42.75 ± 0.78 42.80 ± 0.57

Water absorption (holding), retention (% held), and loss (% in 6 months) of different carrier materialsTabelle 3. Wasseraufnahme (Halten), Retention (% gehalten) und Verlust (% in 6 Monaten) verschiedener Trägermaterialien

Carrier material Water absorbed (ml) Water held (%) Moisture lost (%)
At the start After 6 months
LC 20.56 ± 0.13e 205.6 ± 1.38e 93.13 ± 2.73e 54.71 ± 1.02e
WC 14.08 ± 0.20d 140.86 ± 2.33d 64.86 ± 2.31d 53.87 ± 2.38d
Lignite 7.35 ± 0.11b 73.56 ± 1.15b 44.83 ± 2.84b 38.90 ± 4.83b
VC 7.26 ± 0.13a 72.6 ± 1.24a 41.10 ± 1.61a 43.48 ± 2.65c
FYM 7.53 ± 0.19c 75.3 ± 1.90c 51.33 ± 2.52c 31.86 ± 2.26a
LSD (0.05) 0.39 3.91 6.26 7.49

PGPR (Azotobacter chroococcum 5576) survivability shown as CFU in various carriers as a function of time (days) at room temperatureTabelle 4. Überlebensfähigkeit von PGPR (A. chroococcum 5576) gezeigt als CFU in verschiedenen Trägermaterialien als Funktion der Zeit (Tage) bei Raumtemperatur

Carrier materials PGPR CFU (× 107 per g) as obtained after various periods of storage (d)

0 30 60 90 120 150 180
LC 77 ± 8.19e 147.3 ± 2.30e 104.3 ± 6.00e 98.33 ± 9.49e 77.66 ± 7.83e 27.00 ± 2.08e 8.33 ± 1.20e
WC 70.5 ± 3.48d 90.66 ± 6.64d 64.33 ± 5.60d 32.00 ± 4.04d 18.00 ± 1.73d 10.66 ± 1.20d 3.33 ± 0.33d
LN 53.5 ± 2.33c 82.33 ± 2.96c 35.66 ± 2.02c 31.66 ± 2.18c 22.66 ± 2.02c 9.33 ± 0.88c 2.66 ± 0.33c
VC 33.5 ± 2.60a 46.66 ± 2.90a 23.33 ± 1.76a 16.33 ± 1.45a 10.66 ± 0.88a 1.66 ± 0.66a 0.34 ± 0.04a
FYM 47.5 ± 2.02b 56.66 ± 3.48b 21.33 ± 1.20b 17.66 ± 0.88b 08.33 ± 0.88b 1.00 ± 0.57b 0.14 ± 0.02b

Culture holding coefficients of the selected carrier materialsTabelle 5. Kulturhaltekoeffizient ausgewählter Trägermaterialien

Carrier materials LC WC Lignite VC FYM
CHO 4.69 4.36 6.70 5.50 6.50

Chemical properties of the selected carrier materialsTabelle 2. Chemische Eigenschaften ausgewählter Trägermaterialien

Carrier material N(%) OC(%) pH EC(S/m) Moisture (%) References
LC 0.78 58.60 7.36 597 5.90 Abebe et al., 2017
WC 0.72 49.50 7.01 512 7.20 Sudhakar et al., 2004
Lignite 0.86 29.30 6.58 642 9.80 Rumpel et al., 1998
VC 1.01 25.90 7.10 370 17.58 Packialakshmi and Aliya, 2014; Ravimycin, 2016
FYM 1.83 51.80 6.80 330 15.74 Ravimycin, 2016

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