Immediate Effects of Chemical Fertilization on Crop Yield and Soil Bacterial Diversity: Insights for Sustainable Agriculture

The use of chemical fertilizers is widespread in modern agriculture due to their proven benefits for crop productivity. In this study, we examined the immediate effects of the slow-release chemical fertilizer Osmocote® on plant growth and soil microbial communities in a mono and poly culture regime in controlled pot experiment over a single growth season compared to organic soil amendment treatments- Black soldier fly frass and Humus. Osmocote® addition significantly enhanced the growth rate and yield of cherry tomato (Solanum lycopersicum), basil (Ocimum basilicum), and onion (Allium cepa), confirming its effectiveness in plant growth promotion. However, parallel analysis of soil bacterial communities revealed a substantial decline in overall microbial diversity following Osmocote treatment. This reduction was particularly pronounced among bacterial groups involved in key nutrient cycling processes, such as nitrogen and organic matter turnover. Conversely, Osmocote-treated soils showed an increase in the relative abundance of bacterial taxa known for producing broad-spectrum antibacterial compounds. This shift suggests the possible emergence of a suppressive environment that may hinder microbial recolonization and compromise long-term soil health, even after fertilizer application ceases. In contrast, soils amended with organic fertilizers maintained or enriched microbial diversity. Similarly, the presence of plants positively influenced soil bacterial diversity, with some species exerting stronger effects than others. Notably, co-planting multiple species within a pot elevated microbial diversity to levels comparable to those observed with the most beneficial single species. These observations highlight the potential of integrative strategies combining organic and chemical fertilization, alongside diverse plantings, to support both high crop productivity and sustainable soil microbial ecology. Our findings underscore the immediate negative effects of chemical fertilization, which may have long-term consequences for soil function and plant growth potential and suggest more sustainable alternatives.