# Effect of Precision Nitrogen Fertilization of Grassland on Soil Microbial Structure
## 1 Introduction
Nitrogen fertilizers promote the growth of bacteria that use inorganic nitrogen while reducing the abundance of nitrogen-fixing bacteria, which naturally replenish nitrogen levels in the soil [39]. These shifts affect other critical soil processes, such as phosphorus solubilization and organic matter decomposition. Moreover, long-term fertilizer use stimulates denitriying bacteria, which may lead to increased greenhouse gas emissions, threatening both climate stability and soil fertility [40]. These changes highlight the need to consider trade-offs between immediate agricultural benefits and the long-term health of the soil and ecosystem balance. Land management affects the structure of microbial communities by altering nutrient levels, which can lead to shifts in the dominant microbial groups, such as from bacteria to fungi. Actinomycetes play a special role in the soil ecosystem because they can form symbioses with non-leguminous plants, fixing atmospheric nitrogen. This nitrogen becomes available to both the host plants and other plants in their vicinity. Since nitrogen is one of the key limiting factors for plant growth in the environment, its fixation is crucial for ecosystem productivity. It is estimated that about 15% of globally fixed nitrogen comes from the symbiotic interactions between actinomycetes of the Franklin family and their host plants. Actinomycetes also contribute to improving the availability of nutrients and minerals, synthesizing plant growth regulators, and demonstrating the ability to inhibit phytopathogens [41]. Thanks to these properties, they not only support plant growth but also protect them from diseases. Moreover, actinomycetes operate in an environmentally friendly manner, supporting the biotic balance of the soil by participating in the nutrient cycling process. These actions contribute to the improvement of soil quality and increased crop productivity [42; 43]. Given the crucial role of actinomycetes in soil ecosystem functioning, they can be considered potential indicators of fertilizer efficiency and soil health [44]. Understanding the impact of precise nitrogen fertilization on the microbiological structure of soil is crucial for improving its quality and increasing agricultural production efficiency. Proper nitrogen fertilization management supports microbial activity, which positively influences nitrogen cycling and soil health. In recent decades, numerous studies have been conducted on the impact of various agronomic practices on the abundance, diversity, and activity of soil microorganisms [45; 46; 47; 48; 49; 50; 51; 52; 53; 54; 55]. As [PERSON] et al. [56] point out, long-term monitoring of microbiological parameters, such as microorganism biomass or metabolic rate, allows for a better characterization of the soil's productive potential and the observation of its changes over time. However, reports on the spatial assessment of mineral components in soil based on microorganism abundance are extremely rare, and there is still a lack of studies in this field. Consequently, spatial methods for assessing soil productivity based on these indicators are also non-existent, which was a key motivation for undertaking the research described in this article. The aim of the study was to quantitatively and qualitatively determine the relationship between the presence of actinomycetes and nitrate content in the soil, as well as to analyze the distribution of these microorganisms in the soil profile.