## 1 Introduction  
Grasslands are a major vegetation type that span across the Earth's terrestrial surface [1]. These ecosystems are often dynamic and intricate environments that sustain a host of ecosystem goods and services [2], such as the grazing of livestock, the provision of traditional medicinal plants, the regulation of climate, and the purification of water [3, 4]. In South Africa, the financial appraisal of the ecosystem goods and services provided by grasslands are in excess of ZAR 9 billion [5]. However, unsustainable anthropogenic activities (e.g., overgrazing and intensive agriculture) have caused severe degradation to these environments [6, 7]. To rehabilitate degraded grasslands, as well as maintain the soil nutrient profile, nitrogen-based fertilization regimes are extensively implemented by grassland stakeholders [8, 9]. Nitrogen is the primary constituent of chlorophyll and plant enzymes and is, thus, often the limiting factor of net primary productivity within terrestrial ecosystems [10, 11, 12, 13, 14]. As such, nitrogen regularly forms the basis of fertilizer compounds [13, 15]. Subsequently, the use of nitrogen-based fertilizers has been proven to augment biomass productivity within previously degraded grasslands [9]. However, their excessive use can often have detrimental environmental consequences [13; 14; 16; 17; 18]. The nitrogen cycle is a delicately balanced and highly complex feedback system; however, the continued introduction of anthropogenic nitrogen has adversely altered its natural state [19; 20]. Several studies have emphasised the detrimental impacts associated with excess anthropogenic nitrogen application [18; 21; 22; 23]. These impacts are often preluded by increases in both foliar nitrogen and soil nitrate concentrations [24; 25]. Thereafter, unregulated anthropogenic nitrogen deposition results in the available nitrogen pool exceeding the demand of both plants and microbes, causing the ecosystem to reach a state of nitrogen saturation [16; 24; 25]. This may cause stunted growth, increased mortality, and a reduction in overall species diversity [20; 26]. The culmination of these effects along with the lack of proper grassland management pracises such as overgrazing [27], could greatly alter many sensitive ecosystems [24; 25; 28]. The factors, processes and effects concerning nitrogen saturation have been extensively studied for a variety of ecosystems, including grasslands [13; 16; 28; 29; 30; 31]. Fundamentally, unregulated nitrogen enrichment significantly alters the soil physiochemical environment [18; 28]. This results in nitrate (NO3\({}^{-}\)-N) and ammonium (NH4\({}^{+}\)-N) supplies exceeding both plant and microbial demand [29]. Thereafter, the process of nitrification occurs, as excess ammonium is converted into nitrate [32]. The ensuing high nitrate concentrations coupled with climatic factors (i.e., rainfall) cause negatively charged NO3\({}^{-}\) cations to leach [30]. This in turn causes the soil to acidify as pH levels decrease [33]. Subsequently, both soil acidification and the accumulation of negatively charged NO3\({}^{-}\) cations result in the attraction and leaching of positively charged calcium (Ca2\({}^{+}\)) and magnesium (Mg2\({}^{+}\)) anions into ground water [13; 16; 34]. As such, characterising the initial stages of nitrogen saturation is crucial in preventing the negative consequences associated with over-fertilization. [PERSON] et al. [16], in their study of nitrogen saturation in northern forest ecosystems, documented several initial indicators of nitrogen saturation. These indicators included elevated concentrations of soil nitrate, increased soil acidity, and the increased leaching of minerals [16]. In this context, research documenting the present nitrogen status of grasslands, as well as early indicators of nitrogen saturation in near-real-time are required to facilitate management protocols and optimize biomass production within degraded grasslands, whilst avoiding any possible adverse effects [13].