Screening Of Plant Growth Promoting Rhizobacteria And Development Of Compound Microbial Fertilizers

Continued overuse of chemical fertilizer has led to many negative environmental impacts including destruction of soil structure and soil microbial community,decreasing production and quality of agricultural products.The low efficiency of chemical fertilizer causes environment pollution.Green agriculture cannot be satisfied by only application of chemical fertilizer.However,low available nutrients,slow efficiency and large usage of conventional organic fertilizer would cause loss of the resources and low economic effects.Small dosage,inefficiency and small-scale applications of microbial fertilizer that produced by plant growth promoting rhizobacteria.Combining the advantages of microbial fertilizer,organic fertilizer and chemical fertilizer has a wide applying prospect.This study firstly screened some strains that could produce IAA and ACC deaminase.The results showed that five strains（NJAU-52,NJAU-FAD,NJAU-60,NJAU-69 and NJAU-29）could produce higher IAA(7.8～14.90 mg·L^-1,respectively).And ACC deaminase amounts were 0.18～0.45 U·mL^-1·min^-1 for strains NJAU-54,NJAU-82,NJAU-69,NJAU-53,NJAU-84,NJAU-72 and NJAU-86,respectively.By synthesizing twice results,strains NJAU-FAD,NJAU-25,NJAU-29,NJAU-52,NJAU-53,NJAU-54,NJAU-57,NJAU-60 and NJAU-84 were screened out to conduct pot experiments to investigate their promoting effects.Through the results of pot experiments,four strains（NJAU-52,NJAU-57,NJAU-60 and NJAU-69）were chosen because of the better promoting effect.These four strains were respectively identified as Bacillus endophyticus,Bacillus flexus,Bacillus aquimaris and Bacillus megaterium by 16S rDNA sequencing analysis.Strain NJAU-60 were eventually verified to be the most effective strain after carrying out the pot experiments at the second time.The growth promoting results of strain NJAU-60 treatment were showed as following:the plant height,shoot fresh weight and shoot dry weight of maize were increased by 20%,32%and 20%,respectively;the plant height and chlorophyll content of cucumber were increased by 10%and 12%,respectively;the plant height and chlorophyll content of eggplant were increased by 52%and 6.3%,respectively;the plant height,stem thickness,chlorophyll content,shoot fresh and dry weight of tomato were increased by 16%,16%,13%,33%and 20%,respectively.During the storage period,dilution plating was used to quantify the number of strain NJAU-60 and Bacillus amyloliquefaciens SQR-9 that were composted to be the powdery and granular compound microbial fertilizers at different nutrient levels.After 180 d storage,the number of strain NJAU-60 in the original nutrient and 7%nutrient were 19.5 × ^-1 cfu·g^-1 and 7.3 ×^-1 cfu·g^-1,which were higher than the national standard(≥2.0 × ^-1 cfu·g^-1).And the number of strain NJAU-60 in the 10%nutrient was 2.1 × ^-1 cfu·g^-1 that were approximately equal to the standard.The number of strain NJAU-60 in the 15%nutrient and 20%nutrient were lower than the standard(0.8 × ^-1 cfu·g^-1 and 0.2 × ^-1 cfu·g^-1,respectively).The number of strain SQR-9 in 10%nutrient and 15%nutrient were 11.33 x ^-1 cfu·g^-1 and 7.8 x ^-1 cfu·g^-1,respectively,and were all higher than the standard.The results of nutrient releasing experiment revealed that the release speed of granulated fertilizer was slower than the powdery fertilizer.At the time of 60 d,the weight of 10%nutrient powdery fertilizer decreased 22.7%whereas the granulated decreased 17.4%.At the same time,the weight of 15%nutrient powdery fertilizer decreased 32.3%while the granulated decreased 22%.And in the pot experiment,plants of organic and inorganic compound fertilizer treatment grew better than the only chemical fertilizer treatment at the same nutrient level.Meanwhile,plants of the treatment of powdery compound microbial fertilizer grew better than the treatment of chemical fertilizer.The results of the granulated compound microbial fertilizer treatment were almost the same as that of the powdery fertilizer treatment.