EJSSEurasian Journal of Soil ScienceEurasian J Soil Sci2147 - 4249Federation of Eurasian Soil Science Societieshttp://ejss.fesss.org/10.18393/ejss.183376110.18393/ejss.1833761Effects of a microbial plant biostimulant on soil microbial activity, photosynthetic performance, and grain productivity of winter wheat under greenhouse conditionsBenedict Odinaka Okorie Katya Petkova Dimitrova katia_dimitrova@au-plovdiv.bgDobrinka Anastasova Balabanova 15190-1012025-05-092025-11-262025-12-022026-01-02 Copyright © 2016 The authors and Federation of Eurasian Soil Science Societies Plant biostimulants are widely recognized as an eco-friendly alternative to chemical fertilizers due to their beneficial effects on soil health and plant growth. This study evaluated the effects of a microbial plant biostimulant on soil microbial activity, photosynthetic performance, and grain productivity of winter wheat grown under greenhouse conditions. Four treatments were tested: control (C), microbial plant biostimulant (MPB, 1 kg/ha), chemical fertilizer (CF, 100 kg/ha), and combined application (CF+MPB, CF dose reduced by 25%). The experiment used winter wheat variety KWS Lazuli and each treatment comprised six replications at completely randomized design. Studied parameters included soil chemical analysis, microbial metabolic activity, photosynthetic performance, and wheat grain productivity. The results showed that application of microbial plant biostimulant (MPB) did not affect soil chemical composition but increased soil dehydrogenase activity. Microbial plant biostimulant (MPB) also affected plant growth parameters and grain productivity. The combined application (CF+MPB) showed no synergistic effects and for net photosynthetic rate and grain productivity did not exceed the results obtained with the CF. However, the overall positive trend across studied parameters supports further research on the partial replacement of chemical fertilizers with microbial plant biostimulants under field conditions.Keywords: Grain productivity, microbial biostimulant, soil microbial activity, photosynthetic performance, winter wheat