Objectives Five biostimulants were studied on their yield promotion effect and possible influence on soil enzyme activity and microbial community structure, aiming to provide academic base for their efficient application.

Methods A field trial was conducted in calcareous tidal soil in Yuanyang County, Xinxiang City, Henan Province, China, with maize as the test crop. The tested biostimulants included trehalose, chitosan, humic acid, and γ-aminobutyric acid, all the stimulants were applied into soil in furrow before sowing, and no biostimulant application (CK) was used as control. At the six-leaf stage of maize (jointing stage), plant samples were collected for investigation of dry matter mass, and 0−20 cm soil layer samples were collected for measurement of soil enzyme activity and microbial community characteristics. At harvesting stage, maize yield and yield components were investigated.

Results The five biostimulants showed different promotion effects on the yield and yield components. Compared with CK, humic acid significantly increased root, shoot and whole plant dry weight by 43.1%, 114% and 101%; all biostimulants did not show effect on grain number per ear; trehalose, chitosan and humic acid increased 1000-grain weight by 5.5%, 4.9% and 8.2%; chitosan and humic acid increased single ear weight by 13.6% and 12.5%; humic acid increased yield by 10.2%, while the other biostimulants did not. Compared with CK, trehalose, chitosan, humic acid and γ-aminobutyric acid did not change urease activity significantly, but all increased the alkaline phosphatase activity; trehalose, chitosan and humic acid exhibited similar promotion effect on the dehydrogenase activities (P<0.05); humic acid increased soil microbial biomass by 29.3%, enhanced bacterial, gram-positive and gram-negative bacteria biomass by 43.9%, 48.8% and 40.5%, respectively, without change on the ratio of gram-positive to gram-negative bacteria. Pearson correlation analysis showed that maize yield was positively (P<0.05) correlated with soil microbial biomass, bacteria, gram-positive bacteria, and the dry matter of root, shoot and whole plant (P<0.05), and not significantly correlated with soil enzyme activity.

Conclusions Trehalose, chitosan, humic acid, and γ-aminobutyric acid all showed promotion effect on the maize yield and yield components to different degree, humic acid showed the best promotion effect on the dry matter accumulation of maize roots and shoots, as well as yield, because its wide promotion effect on the biomass of soil microorganisms, bacteria, gram-positive and gram-negative bacteria, and the soil alkaline phosphatase and dehydrogenase activities. So humic acid is the most prospective biostimulant in agricultural productin.