Five maize plant growth-promoting rhizobacteria(PGPR)strains designated as YM1,YM2,YM3,YM4,and YM5 respectively were isolated and purified from the sandy soil. Based on their nitrogenase activity,ability of dissolving phosphorus and potassium, and indole acetic acid(IAA)synthetic quantity,the active microbial inoculum was screened for producing efficient microbial fertilizer. The results of shake flask culture indicated that strain YM4 was observed to have a stronger ability of dissolving phosphorus and potassium,and higher nitrogenase activity accompanied with the strongest synthetic quantity of IAA than other strains. Its nitrogenase activity reached 15.53 nmol C2H4/(h·mL),the transformation amounts of tricalcium phosphate and potassium silicate were 128.90 mg/L,17.40 mg/L respectively, and the synthetic quantity of IAA was 37.18 mg/L. YM4 was identified as Bacillus pumilus based on morphological observation,physiological and biochemical characteristics test and the conserved sequence analysis of 16S rDNA. Compared to the control treatment,pot experiment results suggested that the concentrations of IAA,available nitrogen,phosphorous,and potassium in the potting soil inoculated with YM4 significantly increased by 136.36%,42.1%,67.41%,and 14.29%,respectively ;moreover,the morphologies of plant roots changed significantly,i.e.,the root length,surface area,root volumes and root tips of maize increased by 172.24%,141.73%,112.14%,and 104.53%,respectively ;additionally,the average wet weight,the height of maize,SPAD value increased by 130.07%,150.65%,and 151.56% and the total N,P,K content of maize significantly increased by 120.99%,166.33% and 138.21% respectively. We may conclude that YM4 possess the abilities of efficiently fixing nitrogen,solubilizing phosphorus and potassium,and synthetizing IAA,thus has great application potential in the development and utilization of agricultural production.%从郑州市砂质潮土中分离纯化出5株玉米根际促生菌，通过测定其固氮酶活性、解磷能力、解钾能力以及吲哚乙酸（IAA）合成量，筛选出能够制作高效微生物肥料的活性菌剂。摇瓶结果表明，菌株 YM4具有较高的固氮酶活性，溶解无机磷、钾的能力较强，合成 IAA 的能力最强。其中固氮酶活性达到15.53 nmol C2H4/（h·mL），对磷酸三钙、难溶性硅酸钾的溶磷量和溶钾量分别达到128.90 mg/L 和17.40 mg/L，IAA 的合成量为37.18 mg/L。经形态观察、部分生理生化特征测定及16S rDNA 的保守序列鉴定，确定该菌株为短小芽孢杆菌（Bacillus pumilus）。盆栽试验结果表明，与对照组相比，接种该菌株的盆栽土壤中 IAA、矿质氮、速效磷、速效钾含量分别提高了136.36%、42.1%、67.41%和14.29%；植株根系形态也发生了显著变化，其中根系总长、总面积、总体积、根尖总数分别增加了172.24%、141.73%、112.14%和104.53%；植株鲜重、株高、SPAD 值及氮、磷、钾含量分别提高了130.07%、150.65%、151.56%、120.99%、166.33%和138.21%。该菌株具有高效固氮、解磷、解钾及合成 IAA 的能力，在农业生产的开发利用中具有较大应用潜力。
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