| Agricultural manipulation of symbiotic and free-living plant growth-promoting rhizobacteriahas become a significant component of modern agricultural practice in many countries since plantgrowth-promoting rhizobacteria (eg., Azotobacter, Azospirillum, Pseudomonas) was put forwardto describe the effective bacteria in the root rhizosphere for the first time in the early20th century.Utilizing potential PGPR as inoculants has received considerable attention. However, qualitycontrol of inoculants must be considerable in expansion and commercialization of inoculants,which directly determines the effects of PGPR inoculants in greenhouses or the field experiment.As a matter of fact, the selection of carrier was a key factor of success of inoculation, a largenumber of literatures have been carried out to evaluate maintenance of cell viability and stability,as well as to select cheap carriers to extend the shelf life of plant beneficial bacterial inoculantsfor agricultural crops.In present paper, A mixture of four plant growth promoting rhizobacteria (PGPR), includingBacillus sp. Jm170, Pseudomonas sp. Jm92, Azotobacter sp. Lx191and G, was inoculated todifferent single carriers (mushroom bran, potato pulp, charcoal, cultivate soil, peat and organiccompost) and their compound formulations (F1、F2、F3、F4、F5and F6), respectively to evaluatethe shelf life and the release rate of viable bacteria in different carrier-based inoculants. Agermination experiment was carried out by presoaking the sudangrass seeds(Sorghum sudanense)with different water extract (volume fraction100%,50%,25%and10%) of carriers andbio-fertilizers to determine the effects of water extract on germination parameters (germinationrate, seedling fresh weight, root length, root surface area, root volume and root average diameter)based on agar bed. Meanwhile, a randomized block experiment was conducted to study theeffects carrier-based inoculants on the growth and quality, soil available nutrients and soilmicrobial composition of maize (Zea mays L.)and sudangrass in Xiangquan, Dingxi City ofChina during the cropping season, April to October in2012. The results were obtained asfollows：1. The water absorption rate of different carriers had significant differences. The higherwater absorption of single carriers were CS (cultivate soil) and PP (potato pulp), which reached86.3%and82.2%with wrinkled and spongy-like surface structure, respectively while that of P(peat) was the lowest (42.0%), having a clear three-dimensional reticular surface structure.However, the water absorption rate of different compound carriers was followed by F1>F6>F2>F3>F5>F4, and that of having the same composition presented―1+1>2‖incompletely.2. The water content of different carriers and their formulations were below10%afterair-drying5d on room temperature. The pH value of P and PP were close to neutral, and the restsingle carriers were alkaline while that of compound carriers were suitable for colonization ofPGPR. The nutrient content of single carriers had significant difference, OC (organic compost),MR (mushroom bran) and CS had the maximum nutrient content while minimum of that was C(charcoal). The nutrient content of compound carriers was relevant to their composition.3. The water soluble extract of different carriers and their formulations was non-toxic andtheir available nutrient can significantly promote the growth and reproduction of PGPR. Therelease rate of viable bacteria of C-based inoculants was highest, F3(40%peat+20%charcoal+40%cultivate soil) taking the second place for all carrier-based inoculants storing2days in the28℃incubator.4. In addition to PP and F2(40%peat+60%potato pulp), the viable bacteria of restcarrier-based inoculants, stored at room temperature provided a longer shelf-life than peat-basedinoculants after6months of storage, accorded with the quality criterion of agricultural microbialfertilizer of China (NY227-94). The number of viable bacteria and water content for differentcarrier-based inoculants decreased with extension of storage period. Compared to singlecarrier-based inoculants, the viable bacteria of compound carrier-based inoculants increasedabout100times, and that of F3was the best, F4(20%peat+40%mushroom bran+40%cultivate soil) came second.5. Different volume fractions (10%,25%,50%and100%) water extract of carrier-basedinoculants had significant effects on germination of sudangrass, especially for seedling freshweight (SFW), root length (RL), root volume(RV), root surface area(RSA), root averagediameter(RAD) significantly (P<0.05), the change of each index was single-peak or bimodalcurve with the increase of the volume fraction of extracts, the concentration of25%and50%wasbeneficial to seed germination.6. The seed germination data of different water extract of carriers and carrier-basedinoculants with the volume fraction of25%and50%was further analyzed, the results showedthat the water extract of carrier-based inoculants were superior that of carriers. Principalcomponent analysis indicated the F4(20%peat+40%mushroom bran+40%cultivate soil) was the best for compound carrier-based inoculants for25%treatment group, F1(40%peat+60%charcoal) taking second place while C (charcoal) and OC (organic compost) of single carrierbio-fertilizers were better, PP (potato pulp) was the worst. Compared with CK (sterile watersoaking), SL, SFW, RL and RSA of F4-based inoculants increased by24.4%，28.9%，69.6%and73.6%, respectively.7. Different carrier-based inoculants had no significant effect on the height and fry freshration of sudangrass and maize while it can significantly improved the hay yield of two crops, theincrease rate of sudangrass and maize were6.9%and7.8%on average, respectively. Growthpromoting order of different inoculants on crude protein and total phosphorus content ofsudangrass as follow: compound carrier-based inoculants>single carrier-based inoculants>CK(sterile water soaking). Nevertheless, the effects of different inoculants on total phosphoruscontent of maize was insignificant, the crude protein content of maize increased by more than18.5%on average, F3-based inoculants was the best.8. Different carrier-based inoculants had significant effect on the soil available nutrient oftwo crops. Compared with control (CK, without inoculation), the available phosphorus,exchangeable potassium and available potassium of Sudan grass increased by27.4%,5.7%and7.8%while that of maize increased by17.3%,7.5%and8.6%, respectively, F1and F3having thebest applied effect. Besides, the application of inoculants had significant impact on soil microbialcomposition, especially for the number of soil bacteria.In conclusion, F1(40%peat+60%charcoal),(40%peat+20%charcoal+40%cultivatesoil) and F4(20%peat+40%mushroom bran+40%cultivate soil) can be used as compound carrierformulation for PGPR inoculants while MR (mushroom bran) and OC (organic compost) wereserved as single carrier to produce PGPR inoculants. |
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