THE ROLE OF Rhizobium gallicum INOCULATION IN THE AGRONOMIC PERFORMANCE AND SOIL BIOCHEMICAL PROPERTIES OF THE BEAN (Phaseolus vulgaris L.) PLANT IN RELATION TO HERBICIDE APPLICATIONS

Abstract

Legume cultivation is a strategic agricultural sector that improves soil fertility through biological nitrogen fixation in sustainable farming systems. The symbiosis between legumes and Rhizobium species is central to this process. However, pesticides widely used in modern agriculture, particularly those applied to seeds and soil, are known to impair this symbiosis and the soil microbiota. Although soil microorganisms can sometimes degrade pesticides into harmless compounds, pesticides can also reduce the viability and activity of beneficial microorganisms. Few studies have addressed the effects of soil-applied pesticides on the survival of Rhizobium bacteria, nodule formation, and symbiotic nitrogen fixation. The aim of this study was to determine the effects of two commonly used herbicides on plant growth, nodulation, and soil biological properties in a common bean (Phaseolus vulgaris L.) cultivar. The experiment was conducted under controlled greenhouse conditions in pots containing 4 kg of soil (oven-dry basis). Two soil-applied herbicides widely used in agriculture, Bonaflan and Fist Gold, were tested. After basal fertilization and herbicide application, surface-sterilized dry bean seeds were sown either inoculated or non-inoculated with Rhizobium gallicum. Plants were harvested after flowering, and morphological, physiological, and microbiological parameters were evaluated. Shoot and root length, shoot and root fresh weight, and shoot and root dry weight were measured as growth parameters; nodule number and nodule weight were determined as nodulation parameters; and nitrogen content was analyzed in shoot and root tissues. Soil biological properties were assessed by measuring soil respiration and the activities of dehydrogenase, urease, alkaline phosphatase, and arylsulfatase. Herbicides applied at the recommended doses had statistically significant effects on some growth and nodulation parameters of the dry bean cultivar. The herbicides also significantly affected soil enzyme activities, which are biological indicators of soil microbial activity. These results indicate that agricultural pesticides affect not only target organisms but also the microbial balance of the soil ecosystem and plant–microorganism interactions, which should therefore be carefully evaluated.