Nitrogen (N) in the form of nitrate is a common pollutant in both surface and ground waters. Nitrate-N can readily leach down beyond the root zone in agricultural soils and reach the ground and surface waters. At levels exceeding the permissible limits, nitrate-N makes the ground water unfit for drinking purposes. In surface waters limited by N, phytoplankton productivity is stimulated by nitrate-N resulting in eutrophication leading to widespread hypoxia and anoxia, loss of biodiversity and harmful algal blooms that can damage fisheries and pristine marine environments such as heritage coral reefs [
1]. According to Howarth [
2], as high as 10- to 15-fold increases in N flows in some areas are causing greatly increased coastal eutrophication. Glibert et al. [
3] contended that the problem is exacerbated by the expansion in the use of urea fertilizer which is soluble and mobile in surface water flows.
Widespread pollution of water bodies by nitrate-N due agricultural intensification in the twentieth century in industrialized countries in North America and Western and Central Europe has been of major concern since early 1970s [
4]. It was a direct consequence of applying large quantities of fertilizer N in these countries. Globally, 60% of areas with elevated nitrate-N in ground water occur in croplands [
5]. As only 20% of the total cultivated land is under irrigated agriculture and accounts for about 40% of the global food production, fertilizer N use and loss of nitrate-N to natural water bodies from the irrigated cropland is much higher than from rain-fed agriculture (
http://www.unesco.org/new/en/natura...gures/all-facts-wwdr3/fact-24-irrigated-land/; Accessed 27 January, 2021). Although spatial and temporal distribution of nitrate-N in ground water under cropland will be determined by fertilizer N use per unit area, percentage of area under cereal crops, vegetable and orchards, percentage of irrigated area, per capita agricultural production, livestock per unit area, population per unit area and annual mean temperature, global fertilizer N consumption is increasing almost linearly in response to increasing demand for staple cereal food grains and animal-derived food (Fig.
1). But after the late 1980s, in many developing countries in East and South Asia, fertilizer N consumption increased several fold more than in the developed regions, where levels have stabilized since 1990 (Fig.
1). For example, in 2018, China in East Asia and India in South Asia, having 36.8% of the global population, used 42.3% of 108.7 Mt total fertilizer N consumed globally; North America and Europe consumed only 26.9% (
FAOSTAT; Accessed 25 October, 2020). Of course, Africa and Oceania remained regions where fertilizer N consumption has been very low and is increasing at a very slow pace (Fig.
1). After 2015, fertilizer N consumption in East Asia started declining because China, the major fertilizer N consuming country, recognized the seriousness of the overuse of fertilizers and introduced the action plan for zero growth of fertilizer use [
6]. The changes in fertilizer N consumption patterns in different parts of the world have discernible impacts on nitrate pollution of ground and surface water bodies in different regions. Thus, although leaching of nitrate-N from the soil–plant system is influenced also by climate, soil and other factors, in recent decades nitrate pollution of surface and ground water has emerged as a serious environmental issue in several countries in East and South Asia along with already affected regions in North America and western and central Europe [
5]. Keeping in view that even in countries with low average fertilizer N consumption there exist regions with intensive agriculture and substantial fertilizer N use, nitrate pollution of ground and surface waters as linked with fertilizer N use is now a global issue.