###### Abstract  
In order to protect and remediate soils, organic farming methods have grown in popularity. The aim of the study was to evaluate the effect of rhizobacteria (_Bacillus subtilis_, _Bacillus amyloidoticiens_, _Pseudomonas fluorescens_) and catch crops (undersown red clover alone, undersown Italian ryegrass alone and a mixture of clover and ryegrass) on the microbiological activity of the soil under organic spring barley. In 2019-2021, a field experiment was carried out on an organic farm, randomly in eight variants, each in three repetitions. The following parameters were analyzed: enzymatic activity of dehydrogenogenes (DHA), acid phosphatase (PAC) and catalase (CAT), soil fertility index (BIF), and a number of selected physiological groups of microorganisms (molds, bacteria, and actinomycetes). Compared to the control variant (without catch crops and bacteria), the values of DHA, CAT, and BIF increased significantly in the variant in which rhizobacteria and catch crops were used simultaneously. The highest BIF, of 32, was obtained in 2019, after the application of red clover catch crop + Italian ryegrass + rhizobacteria. PAC activity dropped significantly after the application of the bacterial consortium alone and was lower than the control by an average of 30%. dehydrogenase activity; phosphatase activity; biological index fertility; molds; genus _Bacillus_ and _Pseudomonas_  
14 March 202314 March 2  
Among them, phytoremediation additionally supported by microbes is considered to be an economical and more ecological alternative [2; 3]. In addition, due to changing social awareness and the growing expectations of consumers with respect to the quality of food, it is likely that agriculture will evolve towards sustainable and environmentally friendly technologies, i.e., sustainable, ecological agriculture. Currently, one of the basic premises for the implementation of sustainable agriculture is ensuring high yields and maintaining high food production without increasing the consumption of fertilizers per hectare. In recent decades, soil microorganisms have been successfully used to improve the ability of plants to tolerate biotic and abiotic stresses. Microorganisms belonging to the PGPR (Plant Growth-Promoting Rhizobacteria) group in agriculture can provide excellent support in counteracting the destructive effects of abiotic stress, such as excessive salinity and drought, replacing expensive, environmentally harmful inorganic fertilizers [4; 5; 6]. They influence the proper course of vegetation by direct and indirect stimulation of plant growth. Direct stimulation consists of providing plants with minerals, the synthesis of phytohormones affecting the development of plants (auxins, gibberellins, cytokins), and reducing the level of ethylene, which adversely affects the roots [7]. Indirect stimulation consists of the biological control of phytopathogens by producing siderophores and the mitigation of other abiotic stress factors. The use of these bacteria as an inoculant increases the level of proline and sugars, which support plants exposed to drought stress by reducing the loss of water through the leaves. Scientific studies have documented the abovementioned properties of PGPR, which are particularly strongly manifested by _Bacillus_ and _Pseudomonas_ bacteria [8; 9; 10]. These bacteria used as inoculants not only stimulate the development of plants but also interact with soil bacteria, which usually belong to a different taxonomic group. Thanks to these relations, the size and biodiversity of the bacterial population may increase, which will improve the biochemical properties of soil. Apart from beneficial organisms, catch crops are also an important element of the environment-friendly agricultural policy of the European Union and an important agotechnical treatment. When they are applied in the right amount, composition, and at the right time, they not only provide nutrients to plants but also catalyze biochemical changes in soil and thus improve its fertility.