## 3 Soil Features as a Consequence of Reduced Fertilization
As a consequence, the formation of soil aggregates diminishes, leading to a more compacted structure with reduced water-holding capacity [WHC] [23,30]. It was proved that increased N fertilization had no significant influence on OM content because mineral fertilizer application could increase OM levels by returning crop residue to the soil; meanwhile, C mineralization led to a decrease in OM content [23]. The amount of N released during OM decomposition directly influences the amount of N consumed by soil microorganisms and the mineralization rate [30]. The effect of humidity on N dynamics in the soil environment is complex and dependent on the specific environmental conditions [30]. Increased humidity can lead to increased transpiration and microbial activity, leading to a faster rate of N uptake and processing by plants and soil microbes [30]. However, prolonged higher humidity can also result in decreased plant growth and N uptake due to water stress [30]. Over time, this depletes the soil's fertility, increasing its susceptibility to degradation. Conversely, excessive N fertilization, particularly in the form of synthetic fertilizers, can lead to soil acidification [35], especially in soils that are more sensitive to acidity fluctuations, such as sandy and loose soils. Soil acidification leads to a reduction in microbial diversity, as most soil microorganisms, including bacteria and fungi, thrive in a pH range of 6 to 7. When the pH drops below 6, certain microbial species, particularly those responsible for N processing, exhibit decreased activity or may even become extinct [36,37]. This phenomenon disrupts critical biogeochemical processes, such as the N cycle, potentially resulting in the reduced availability of essential nutrients for plants. Additionally, acidification disrupts the soil's cation exchange complex, causing the leaching of critical elements like calcium [Ca], Mg, and potassium [K] [36]. It is also important to consider that this loss of essential cations not only affects plant growth and nutrient uptake but also further exacerbates the decline in microbial diversity, as many beneficial microbes depend on these cations for their metabolic processes [37]. The diminished activity of microorganisms accelerates the degradation of the soil structure, which can lead to a loss of the soil's capacity to retain water and nutrients, thereby increasing the risk of erosion [38]. Consequently, improper land management practices and the excessive application of N fertilizers can give rise to long-term ecological challenges, adversely affecting agricultural productivity and hindering sustainable environmental development [19,23,24]. This interplay between soil acidification and microbial health underscores the importance of adopting sustainable agricultural practices that promote soil health and maintain the balance of microbial communities essential for ecosystem function [36, 37, 38]. The mechanism by which N is assimilated and its amount in the soil environment is highly dependent on soil type (Figure 4). Sandy soils, characterized by low water retention capacity and poor structural integrity, are prone to significant N losses through leaching, particularly in the form of NO\({}_{3}\)\({}^{-}\), leading to the rapid depletion of essential nutrients [39,40]. In contrast, clay soils, which exhibit greater compaction and higher cation exchange capacity [CEC], are more efficient at retaining N, with slower ion exchange processes that facilitate prolonged N availability [30]. Chernozem soils, rich in OM and microbial populations, efficiently process and stabilize N, resulting in enhanced soil structure and a more balanced nutrient profile. Heavy, poorly permeable clay soils retain N for extended periodsbut are susceptible to acidification under conditions of excessive fertilization [41]. Therefore, reduced and balanced N fertilization rates are essential to prevent soil degradation and maintain long-term agricultural productivity [19; 24].