## 3 Soil Features as a Consequence of Reduced Fertilization
### Soil Biology
#### 3.2.1 Enzymatic and Respiration Activities in Soil  
Enzymes involved in the N cycle are particularly sensitive to reduced N fertilization because many of these processes depend on N availability in the soil. In the literature, there are various opinions regarding the role of reduced mineral fertilization in shaping soil enzymatic activity. Reduced N fertilization has a significant impact on enzymes related to the decomposition of OM and the N cycle in the soil [23; 77].  
Although reduced N fertilization may lead to a decrease in enzymatic activity in the short term, the soil often adapts to new conditions [32]. In the longer term, microorganisms that are better adapted to environments with low N availability may increase their activity. Such organisms include N-fixing bacteria and mycorrhizal fungi, which can support plants in assimilating N from organic and atmospheric sources, partially compensating for the reduced enzymatic activity [74; 75; 76].  
One of the main enzymes involved in the decomposition of OM is cellulase, which breaks down cellulose, the primary component of plant cell walls. Under conditions of reduced N availability, the activity of microorganisms producing cellulase may decrease [63]. Microorganisms require N to build proteins and enzymes, and a lack of N limits their capacity to efficiently process OM [17].  
Similarly, enzymes such as proteases, which break down proteins into amino acids, also show decreased activity under reduced N fertilization because these enzymes are directly involved in the processing of organic N [66; 78].  
Enzymes such as urease, responsible for breaking down urea into NH\({}_{3}\), and nitrifying enzymes are critical in the N cycle [32]. Under reduced N fertilization, urease activity decreases because microorganisms have less substrate (urea) to process [78; 79]. Similarly, a reduction in NH\({}_{3}\) levels leads to decreased nitrifying activity, limiting the conversion of N into forms more accessible to plants [35]. At the same time, the reduction in the availability of easily assimilable forms of N promotes the development of N-fixing bacteria, such as _Rhizobium_, which compensate for deficiencies by fixing atmospheric N\({}_{2}\)[33].  
Soil dehydrogenases are enzymes critical for the respiratory processes of microorganisms, reflecting their overall metabolic activity in the soil. Their action involves catalyzing the oxidation reactions of organic compounds, which is directly related to the C cycle and the processes of OM decomposition [80]. According to [PERSON] [81], as well as research conducted by [PERSON] and [PERSON] [82], high doses of fertilization contribute to an increase in the activity of this group of enzymes. Under conditions of the reduced availability of this element, enzymatic activity may decrease, which should be monitored through the implementation of long-term studies. However, according to research conducted by [PERSON] et al. [83], no negative impact of reduced N fertilization on dehydrogenase activity was noted in soils under rapeseed and wheat cultivation.  
Soil respiration, which serves as a measure of microbial activity, also changes under reduced N fertilization [84]. Microorganisms that heavily rely on N for their metabolic processes exhibit decreased RA under conditions of the low availability of this element, leading to a decline in respiration. Soil respiration, the process of releasing CO2 by microorganisms and plant roots, is directly linked to the decomposition of OM and the C cycle [85]. Reduced N fertilization slows down the decomposition rate of organic compounds, which can hinder the C cycle in the soil [45; 46].