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Table 1 Effect of co-applied PGPR and biochar under normal conditions on plant productivity and soil quality

From: Unlocking the potential of co-applied biochar and plant growth-promoting rhizobacteria (PGPR) for sustainable agriculture under stress conditions

Strain

PGPR traits

Biochar production and application rate

Crop

Experimental details

Impact on plant productivity and soil quality

References

Micrococcus yunnanensis

Organic and inorganic phosphate solubilizing, siderophore producing

Sugarcane bagasse derived biochar

Pyrolyzed at 550 °C for 4 h

Levels of BC application: 0, 1 and 2% w/w

Barley (Hordeum vulgare)

Green house experiment

Plants were grown for 7 months

PGPR + 2% biochar treatment increased soil microbial biomass by 11% than un inoculated control (no PGPR, no biochar). Biological yield in PGPR + biochar was 42.1 g/pot, 38.9 g/pot in PGPR only and 36.3 g/pot in biochar only treatments

1000-kernel weight and phosphorus uptake was increased by 9% and 8% than PGPR alone treatment, respectively

[41]

Paenibacillus polymyxa and Bacillus amyloliquefaciens

 

Biochar was made from millet straw

Level of BC application: 2% w/w

Tomato (Lycopersicon esculentum)

Green house Pot experiment

Co-application of biochar and PGPR was evaluated in presence of absence of chemical N fertilizer

In combined PGPR + biochar + nitrogen application soil urease, ammonium, and nitrate was significantly increased between 14 and 45%, 137%, 31–87%, respectively, than nitrogen + PGPR and nitrogen + biochar

Relative abundance of Nitrospira and Bradyrhizobium were increased in the soil

The tomato yield was 32.45%, 45.69%, and 10.44% higher than those in the nitrogen, nitrogen + PGPR, and nitrogen + biochar treatments, respectively

NUE (nitrogen use efficiency) increased by 11–18%

[43]

Bacillus lentus, and Pseudomonas fluorescence

Phosphate solubilizing

Biochar was prepared with cow manure, wheat straw and oak wood

Pyrolyzed at 300–500 °C

Safflower (Carthamus tinctorius)

Farm assay was conducted for period of 2 years (2017 and 2018)

Highest grain yield of 1527 kg ha−1 was found in PGPR + biochar treatment

Whereas grain yield by wheat straw biochar application alone was 1452 kg ha−1 and wood biochar was 1385 kg ha−1

[49]

Bradyrhizobium japonicum and Pseudomonas putida

NDA

Maize residues were pyrolyzed at 600 °C for 30 min

Soybean (Glycine max)

Green house experiment

Control: soil with uninoculated, 1 and 3% biochar

PGPR strains with 1 and 3% biochar

Plant growth duration was 30 days

PGPRs + 3% biochar increased soil mineral nitrogen content by 73%, available phosphorus by 173%, and available potassium content by 17%, as compared to the 3% biochar only treatment

It also increased protease activity by twofold, alkaline (1.25-fold) and acid phosphomonoesterase (1.52 fold) than PGPRs only and PGPRs with 1% maize biochar treatments

Seed germination increased by 20%, root length by 76%, root dry weight by 56%, shoot length by 41% and shoot dry weight by 59% than the 3% biochar only treatment

[44]

Bacillus megaterium

Nitrogen-fixing, plant-probiotic

Wheat (Triticum L.) straw was carbonized at 600 °C for 3 h

Application rate of biochar used: 20 t hm−2

Eucalyptus (Eucalyptus globulus)

Field experiment; PGPR(2 ml) + biochar (0.18 kg)

In PGPR + biochar treatment; nitrate, inorganic nitrogen, total potassium, EC (electrical conductivity) and soil water content were, respectively, 68%, 45%, 21%, 35% and 24% higher than PGPR only and, respectively, 22%, 16%, 30%, 5% and 18% higher than biochar only treatment

[45]

Pseudomonas sp.

 

Maize straw was pyrolyzed at 360 °C

Application rate was 30 g/pot

Celery (Apium graveolens L.)

Solar greenhouse experiment

Plants growth duration was 8 week of growth. High and low phosphorus (P) level and fungi was also combined with PGPR and biochar

PGPR + biochar increased P uptake by 24.5% and 72.1% than biochar only and PGPR only treatments

Adding Pseudomonas sp. along with fungi and biochar increased root volume by 26–36% and 23–61% than fungi + biochar at high and low P, respectively

It also increased root surface area by 27–73% at high and low P level, respectively, than using fungi + biochar

[39]

Alcaligenes sp.

Phosphorus and zinc solubilization, ACC deaminase activity, and IAA and siderophore production

Biochar source was maize straw

Application level of biochar: 0.5 tons ha−1

Maize (Zea mays L.)

Field experiment; combined application of biochar, rock phosphate enriched compost humic acid and Alcaligenes sp. AZ9

PGPR + biochar increased bacterial population by 30%, and 15%; and microbial biomass carbon up to 12% and 6%, than PGPR and biochar only treatment

Soil organic carbon and saturation percentage increased by 29% and 14%, respectively, than control (No additives)

Adding PGPR with biochar increased shoot fresh biomass, shoot dry biomass, plant height, grain yield and 1000-grain weight by 9, 12, 6, 14 and 5%, respectively, than PGPR only

Combined treatment increased 1000-grain weight by 10%, grain yield by 31%, and stover yield by 34% than control (No additives)

[50]

Bacillus deuterium and Bacillus megaterium

Nitrogen fixing, plant-probiotic

Wheat straw (Triticum L.) was pyrolyzed in a continuous carbonizer at 550 °C for 3 h

Application level of biochar:

BC0, BC20 and BC40 (0, 20, and 40 t hm−2, respectively)

Eucalyptus (Eucalyptus globulus)

Field experiment

Sucrase activity was 48%, 31% and 55% higher in PGPR + BC40 than the PGPR only, PGPR + BC20 and B20 treatments

PGPR + BC40 significantly increased EC than PGPR, BC20 and PGPR + BC20 treatments

[51]

Bacillus sp.

Burkholderia sp.

Phosphate solubilizing, siderophores and IAA production

Biochar was prepared from agricultural wastes

Pyrolyzed at 600 °C

 

Pot experiment: plant growth duration was 90 days

Burkholderia + biochar treatment increased WHC (16%), EC (66%), SOC (16%), available phosphorus (79%), available nitrogen (15%) and hydrogenase activity (40%) than control treatment (without PGPR and biochar)

Combined application of biochar and PGPR increased germination (18.06%), shoot fresh and dry biomass (72.5% and 45.5%, respectively) and root length (113%) over control treatment (without PGPR and biochar)

[52]

Lysinibacillus fusiformis and Bacillus subtilis

Phosphate solubilizing

Biochar was prepared from woody sawdust

Pyrolyzed at 350 °C for 10 min

Application level of biochar (Bagasse and sawdust biochar): 1% (30/3 kg soil)

Maize (Zea mays L.)

Green house pot experiment

Plant growth duration was 65 days

36.2% more nitrogen and 58.3% more phosphorus was found in PGPR + biochar treatment than untreated control

PGPR + sawdust biochar increased root and shoot length by 45% and 64% than the uninoculated and untreated control

PGPR + biochar increased plant phosphorus (72.5%), nitrogen(32.8%), and potassium (42.1%) than untreated control

[53]

Stenotrophomonas sp.

Nitrogen-fixing bacteria

Biochar was prepared from empty fruit bunch of oil palm

Pyrolyzed at 350–450 °C

Application level of biochar: 0, 0.25, 0.5, 0.75 and 1% of soil (lab experiment)

Biochar levels: 0, 5, 10, 15 and 20 t/ha (Green house experiment)

Sweet corn

Lab as well as greenhouse experiments

PGPR + 0.5%biochar treatment showed pH 5.7 (highest) and in PGPR treatment it was 4.7. Nitrogen, phosphorus and potassium were 94.5%, 65.93% and 75.30% higher in PGPR + biochar, respectively, than PGPR treatment

Plant weight increased from 48.5 g plant−1 (in 5 t ha−1 biochar) to 61.4 g plant−1 (in PGPR + 5 t ha−1 biochar)

[54]

Pseudomonas species, Azotobacter chroococcum and Azospirillum brasilense

IAA producing and phosphate solubilizing

Biochar was produced from rice husk

Application level of biochar: 3.6 g kg−1 soil

Rice (Oryza sativa)

Pot experiment; rice grown in alluvial soil in Kharif season

Rice husk biochar + PGPR increased growth and dry matter yield of rice than untreated control

[55]

 

Nitrogen fixing and phosphate solubilizing

Biochar was produced from soft wood chips

Pyrolyzed at 500 °C Application level of biochar: 20 Mg ha−1

Switchgrass (Panicum virgatum cv. Cave-in-Rock)

Field experiment; Plant growth duration was 3 years at two research sites

Plant height increased from 1 to 8% in both biochar + PGPR (nitrogen-fixing) and biochar + PGPR (phosphorus solubilizing) bacteria treatment than control (No PGPR, no biochar)

[56]

Bacillus sp.

Phosphate solubilizing

Biochar: application rate was: 15 g kg−1 of soil

French beans (Phaseolus vulgaris)

Pot experiment; plant growth duration was 8 weeks

PGPR + biochar treatment, increased no. of phosphate solubilizing bacterial count 2.95 ± 0.11 × 106 in the rhizosphere of plants than the PGPR 1.82 ± 0.06 × 106

The shoot biomass (3.22 g), root length (14.88 cm) and root biomass (1.85 g) were significantly higher in the PGPR + biochar treatment compared to PGPR treatment where they were 2.34 g, 13.13 cm, and 1.31 g, respectively, as well as than biochar treatment where they were 3.19 g, 13.12 and 1.75, respectively

PGPR + biochar increased percent nitrogen content 1.64 shoot/g then PGPR treatment 1.24shoot/g and biochar treatment 1.31 shoot/g

[40]