The use of sewage sludge in agriculture is becoming an increasingly important component of sustainable waste management strategies. However, its effective implementation requires a detailed understanding of the processes occurring in soil following application. The aim of this study was to evaluate the dynamics of transformations of organic nitrogen, nitrate nitrogen (NO₃⁻), available phosphorus, and organic carbon in response to varying doses of sewage sludge. The experiments were conducted under field conditions, with temporal monitoring of changes using standard elemental analysis as well as spectrophotometric and colorimetric techniques. The analyses revealed a clear increase in organic carbon and phosphorus content, indicating the activation of processes that enhance soil fertility. At the same time, an intensification of short-term nitrate leaching was observed, particularly in the initial stages following application, highlighting the sensitivity of the soil system to both the rate and timing of sludge incorporation. The results clearly demonstrate that the optimization of application parameters, both in terms of dosage and timing, is crucial for improving process efficiency while minimizing environmental risk in environmental engineering practice.