## 2 Yielding as an Effect of Reduced N Fertilization
When N is plentiful, plants can produce more chlorophyll, enhancing their ability to capture light and perform photosynthesis more efficiently. This leads to increased C fixation and greater biomass production [7; 17]. Furthermore, plants that receive sufficient N are capable of producing more leaves, thereby increasing their photosynthetic surface area and maximizing the conversion of solar energy into OM [17]. N also influences the processes of flowering and fruiting, which is particularly important for crop species such as cereals, vegetables, and fruits. High N availability promotes the development of seeds, grains, and fruits, thereby improving both the quality and quantity of the harvested products [17; 18; 21]. Figure 1: The role of nitrogen in photosynthesis. Gln: glutamine; Glu: glutamate; AKG: alpha-ketoglutate (own work by [PERSON]). Figure 2 illustrates the relationship between varying N fertilizer levels and crop yields across different soil types, categorizing them into deficiency, optimal, high, and excess levels. These yield values are indicative, designed to elucidate rational N fertilization practices. Under deficient N conditions, crops display symptoms such as stunted growth and chlorosis, signaling poor health and insufficient nutrient availability. Conversely, excessive N application can lead to reduced yields despite initial growth spurts, as seen in clay soils versus sandy soils. This nuanced understanding, supported by Figure 2, underscores the importance of tailored fertilization strategies to optimize yield while minimizing environmental impact. One of the primary signs of N deficiency is stunted growth, where plants appear smaller and less vigorous compared to those receiving adequate N [22; 23]. This deficiency often manifests as yellowing leaves, particularly in older foliage, a condition known as chlorosis, which impairs photosynthesis and overall plant health [23]. Ultimately, N-deficient plants produce significantly lower yields, as evidenced by the \"Deficiency\" section (Figure 2). Conversely, an excess of N can lead to detrimental effects on crop yield and quality. Over-fertilized plants may develop scorched leaf tips and margins due to nutrient toxicity, which is referred to as leaf burn. Additionally, excessive N can cause rapid growth, resulting in tall, weak stems that are more prone to lodging or falling over. Interestingly, while crops may initially show increased growth with higher N levels, excessive application often results in lower yields, as reflected in the \"Excess\" section (Figure 2). It is essential to note that with a balanced fertilization strategy and proper attention to the physical, chemical, and biological parameters of the soil, it is possible to maintain high yields even with reduced N applications [23; 24]. This approach not only promotes sustainable agricultural practices but also enhances soil health and reduces the environmental impact associated with excessive fertilizer use [24]. Balanced N fertilization tailored to crop growth stages and specific cultivation requirements maximizes yields while minimizing the ecological footprint [23]. This is particularly important in the context of contemporary challenges related to environmental protection and sustainable agriculture [24]. However, N application must be carefully managed to avoid its excess in the soil. Excessive N fertilization can result in undesirable effects, such as excessive vegetative growth at the expense of reproductive structures, which negatively impacts fruit or grain quality [17; 21]. Additionally, N surpluses can lead to nutrient losses to the environment, including leaching into groundwater, where it contributes to pollution, and emissions of nitrous oxide [N\({}_{2}\)O], a potent greenhouse gas [19; 22]. Therefore, N fertilization requires precise adjustment to the needs of the plants and soil conditions [23].