Introduction

Nitrogen is an essential fundamental building block for life. It is the most plentiful element in the earth’s atmosphere, yet it’s molecular from N₂, it is unusable by the vast majority of living organism. It must be transformed or fixed into other forms collectively known as reactive nitrogen, before it can be used by most plants and  animals. Without an adequate supply of nitrogen, crops do not thrive and fail to reach their maximum production potential. In many ecosystem nitrogen is the limiting element for growth. However when present in excess reactive nitrogen cause a range of negative environmental effects, poses risk of human health and consequently can have negative economical and social consequences. This non technical review seeks to convey an understanding of the effects of reactive nitrogen in the environment. Focusing mainly on those caused by excesses of reactive nitrogen. It also examines experience with some polices developed to address those effects and offers recommendation to advance understanding and policy response to them.

Natural production of reactive nitrogen includes nitrogen fixation by legumes blue green algae and few other organisms and by lightning.

Although substantial amounts of nitrogen are fixed through naturally occurring processes those rates are not sufficient to meet the food demands of an increasing world population. Because of this scientists and technologists have found ways to increase it's availability by artificially fixing nitrogen and producing synthetic fertilizers. Application of reactive nitrogen in the form of synthetic fertilizers plays a central role in modern crop production.

The pool of reactive nitrogen in the world's nitrogen cycle is continually increasing. To work towards halting or reversing this increase. We should also address the efficiency with which reactive nitrogen is used.

Loss of nitrogen soil:

 There are four main ways by which nitrogen is lost from soil. The ways are:

1.Volatilization loss

2.De-Nitrification loss

3.Leaching loss

4.Used by soil microorganisms and weeds.

These ways of nitrogen losses are briefly described as follows:

1.Volatilization loss:

In this chemical reduction process, nitrogen is lost in the gaseous form when urea or ammonium fertilizers are applied on the soil surface.

Losses of nitrogen as ammonia is occurred especially in alkaline soil. High concentration of ammonia (high dose of ammoniacal or amide fertilizers) is toxic to the nitrification process, resulting is an unusual build up of nitrites.

Under acid conditions these nitrites are converted to gaseous elemental nitrogen or nitrous oxide, when brought in contact with certain ammonium salts or urea

It may be represented in the following reaction:

2HNo₂+CO(NH₂)₂   ---> CO₂+3H₂O+2N₂()

2.De-Nitrification loss:

The nitrates may change to gaseous form in the lack of air or by poor drainage. The biological reduction of nitrate-nitrogen to gaseous compounds by microorganisms is called de-nitrification. The microorganisms involved are common anaerobic forms.

Under field conditions, nitrous oxide is the gas lost in largest quantities, although elemental nitrogen is also lost under some conditions. Nitric oxide loss occurs most readily under acid conditions.

       Reaction:

       2NHO₃     2NHO₂  NO₂  N₂  2NO

3.Leaching loss:

The nitrate-nitrogen is lost in drainage or with percolating water. The amount of nitrogen lost depends upon the climate and cultural conditions. In humid region or a water-logged conditions, losses of nitrate by leaching are significant. In arid and semi-arid regions, such losses are minimum.

4.Used by soil microorganisms and weeds:

Soil microorganisms readily assimilate nitrate-nitrogen. It microbes have a ready food supply.(OM) they utilize the nitrates more readily. This is one of the reasons, crops get about one-half the nitrogen added in forms of nitrogenous fertilizer. Weed may also utilize the nitrate-nitrogen added to the soil or present in soil. Therefore crops may not get nitrogen in full quantity.

Nitrogen use efficiency (NUE):

NUE can be defined and measured in various ways. Two specific definitions of NUE are offered by Jervis et al,2011:

1.The direct recovery efficiency:

This is the proportion of added nitrogen as fertilizer that is successfully utilized and converted into food(either crops or livestock).

2.The indirect recovery efficiency:

This is the increase in total biomass yielded divided by the amount of nitrogen applied. However in broad agriculture focuses on minimizing damaging emissions of nitrogen from agriculture systems that also maximizing the benefits gained.

The way NUE is defined and measured will very according to context and can apply to sectors other than agriculture. For mistake because nitrogen pollution is emitted from fossil fuel combustion. Such as in car engines and coal and gas-fired power stations. The ratio of nitrogen emitted to benefit can be calculated.

Importance of nitrogen use efficiency (NUE) in agriculture:

It is important to consider NUE in agriculture for the following reasons:

1.Agriculture is the significant source of nitrogen pollution.

2.There are major insufficiencies agriculture's use of nitrogen.

3.Reactive nitrogen is central to agriculture and it's efficient use will be of critical importance to ensuring food security around the world.

Reactive nitrogen is essential to agriculture to create amino acids and carbohydrates in plants to feed animals and humans.(Ehrisman et al. ,2007)

However, agricultural usage of reactive nitrogen now makes it the dominant source of nitrogen pollution in many parts of world wowing to high rates of artificial fertilizer use and insufficient use of manures(Leip et al., cited by Brick et al.,2011)

Nitrogen use is becoming less efficient in agriculture; the global NUE of cereals decreased from 80% in 1960 to 30% in 2000'(Erisman et al.,2007).

Economic benefits of improving NUE in agriculture:

1.Reduced input costs, particularly from reducing expenditure on bought in synthetic fertilizer. Synthetic fertilizers is often considered a cheap way to boost yields and thus economically attractive to farmers, it is nonetheless a cost and one that is likely to rise as reduced availability of fossil fuels affects the price of fertilizers.(Sutton et al.,2011a)

2.Reduce output costs instead of treating organic by products such as animal manures and plant residues as wastes farmers may look at NUE practice which recycle these nutrients onsite further minimizing input costs, as well as potentially reducing the time and financial costs of waste disposal.

3.Improved yields may result from improving the efficiency of reactive nitrogen is uptake by crops and livestock.

4.Improved quality may result from improving NUE and thus potentially improve the value of a farmer's produce.

5.Improved sustainable yield. If NUE gains are purchased in ways that move agriculture towards increasing sustainability farmers and society stand to gain from future-proofing their businesses.

6.Improved ecosystem services and reduced externalized costs. NUE measures could contribute to improved ecosystem services which build natural capital. For example, healthier soils retain water and reduce social costs of flooding. Externalized costs, such as those for de-polluting water would also be reduced.

The importance of reactive nitrogen to food security:

It is said that reactive nitrogen in synthetic fertilizers feeds 40% of the world's population (Jackson cited by Sutlom and Billen,2010).with a rising global population, agricultural demand for reactive nitrogen will increase be it in synthetic or organic forms. A doubling of global fertilizer use has been predicted for the 21st century, partly driven by increasing demand for biofuels. The rising global population increases demand and potentiality competition for energy and fertilizer, thus the efficiency of nitrogen fertilizer needs to be greatly increased to avoid compromising global food security.

Methods of improving nitrogen use efficiency in agriculture:

A large number of potential co-benefits from improving NUE in agriculture have been recognized but questions remain on how they are to be achieved, and the relative merits of alternations to mainstream agriculture composed with more radical overhauls of entire agricultural systems.

Loss mainstream forms of agriculture from organic forming to agro-ecology, consideration agriculture restoration agriculture and permaculture, increasing emphasis the role of microbes in providing crop nutrition and maintaining healthy soils and the value of soil amendments to balance carbon and nitrogen for optimal soil composition.

Various practice of more sustainable agriculture which could reduce nitrogen pollution that increasing NUE. Such as minimal tillage, intercropping, cover crops, catch crops, green manures animal imbrues, broad crop rotation, effective use of crop residues and landscape planning (Jarvis's et al.,2011);

Theories and  techniques from alternative agriculture (such as permaculture, natural farming and agro-ecology) which may warrant investigation include :

          Fertilizer measures, such as building bio-logical fertility( e.g. storing nitrogen in microbial life) and diverse nutrient density through mulching, compost teas, and composting of human and animal manures.

          Soil management approaches such as no-till systems which better preserve fungi, bacteria and other microbes which may assist in retaining soil nitrogen.

          Crop systems, such as Bi-cropping, poly-cultures , use of potential plans ( rather than reliance on annuals) and associated techniques of Agroforestry , alley-cropping  and food forest.

          Integration of animals , through varies animal-crop systems , holistic management of pastures.

          Water management ( one of the variables  which may influence NVE ) , such as sustainable capture ( e.g. through dams , swales , soil organic matter ) and usage (drip irrigation)

          Design of farming system , through application of Agro-ecological  and other landscape design.

Biodiversity and nitrogen :

Excessive emission of reactive nitrogen are one of the main cause of Bio-diversity loss. Even very low input levels can have a deleterious effect on certain species and ecosystem . without an effective strategy to reduce emission of reactive nitrogen compounds , it will be next to impossible achieve nature conservation targets and comply with conservation regulation , for example with the portion of species and the restoration of habitats to a “favorable conservation status” or the prevention of the “deterioration of natural habitats”. Processes , such as edification , nitrogen loading and species loss irreversible or only reversible over long periods of time . the limit values that has been set for the protection of human health are usefully inadequate for protecting more sensitive species and ecosystem .

The key mechanisms that come into clay here-are-triplication ( nutrient enrichment) and edification ( reduced values resulting from base leaching)-alter species composition , reduce species numbers , and weaken  resilience against shocks , such as the stress caused by drought and frost .

The visible effects of this mechanisms include:

The loss of species-rich meadows and field margins rich in wild herbs;  The formation of excessive sea foam included by algae blooms; and the substantially greater abundance of plants such as blackberry’s and nettle that thrive on nitrogen-rich forest soil .

The impact of this phenomena on bio-diversity is in turn detrimental to ecosystem services , including the recreational value of landscapes. Also ecosystem services for agriculture are affected; when elevated nitrogen inputs resulting the loss of flowering plants, then the foods sources for in souls are lost, and the insects are no longer available for either pollination or as food for birds.

          Effects of excess nitrogen application on climate change :

Nitrous oxide is consider a ‘direct’ greenhouse gas (GHG), since it traps solar radiation in atmosphere and has a warming effect. Nitrogen oxide emissions, however, have indirect-effects through their contributions in the atmosphere, reaction which generate oxen(O3). It has a warming effect when in the troposphere, but cooling effect when in the upper atmosphere (stratosphere). (Galloway et al; 2008).

(A)Warming effects :

(1)        Nitrous oxide :

It is released in large amounts each years and has a positive radioactive force, i.e. its molecular stone thermal radiation from the sun. Thus contributing directly to the warming of the atmosphere. Per unit of weight, nitrous oxide is a more powerful greenhouse gas CO2. Galloway et al, (2007) calculate that, over a 100-year period, nitrous oxide has a global warming potential 296 times larger t hen an equal mass of CO2.

(2)nitrous oxide and agriculture : 

The major driver for changes in atmosphere nitrous oxide concentrations is the increased of reactive nitrogen fertilizer in agricultural mainly through emissions from soils, that have been applied with reactive nitrogen either in the form of synthetic fertilizer or in the form of  measure. This fertilizer increase the reactive nitrogen available to denitrifying microbes which release gaseous nitrous oxide into the atmosphere.(as well as nitrogen)

The Intergovernmental Panel on Climate Change(IPCC, united in the ENA) estimate that, globally 1% of applied nitrogen is released directly as nitrous oxide and another 0.4% indirectly.(later in the nitrogen cascade).

(3)Nitrous oxide from sewage treatment and waste management :

Nitrous oxide is emitted as result of bacterial processing of nitrogen in wastage. The amount released depends on the level of oxygen in the process, being highest at relatively low oxygen levels but decreasing at either very low or very high oxygen levels. Annual nitrous oxide emissions from waste water treatment has been estimated at 25.7Gg of nitrogen, representing about 5% of total nitrous oxide emissions. 

(4)Nitrous oxide from fossil fuel combustion :

Combustion of fossils fuels in energy production, industry and transportation, car result in release of nitrous oxide particularly at medium temperature(500-600C). Whilst combustion of fossil fuels in notorious as a key emitter of CO2, it is considered to be a only minor source for nitrous oxide emissions. The European Environment Agency (cited bg Butter Bach- bawl et. al., 2011) report power station emit quantities of nitrous oxide equivalent to 7.6 Tg of CO2. They calculate transport combustion (of diesel and gasoline) to release 13.4 Tg CO2, a small fraction of the agricultural emissions of nitrous oxide.

(5)Nitrous oxide emissions from natural and semi-natural ecosystems :  

Ecosystems emit nitrous oxide to the atmosphere  through natural porous of de-nitrification. However, the rate at which they do so has been modified by human activity increasing the quality of reactive nitrogen in those ecosystems, for increasing following leaching of reactive nitrogen from agricultural systems or deposition of reactive nitrogen from air pollution. 

(B) Further climate impacts of excess nitrogen:

(1)        Reactive nitrogen, tropospheric ozone and carbon sequestration :

Nitrogen contributes to the formation of troposphere ozone. This affect the carbon cycle, as troposphere ozone impacts photosynthesis and this reduces carbon sequestration. Galloway (2008) raises this possibility and draws attention to uncertainties in how tropical ecosystems will response to rising reactive nitrogen inputs, as most research has been undertaken in  northern latitudes. This is an important question given that tropical ecosystems are expected to received ‘The most dramatic increase’ in reactive nitrogen in the future and are already under pressure from a warming climate.

(2)        Reactive  nitrogen and methane:

A significant issue for the carbon cycle is how reactive     nitrogen    pollution affects methane (CH4) levels. Methane is a greenhouse gas over 20times more powerful than CO2(over a 100s-year period). Just as reactive nitrogen can influence levels  of soil carbon and oxidation processes which release CO2, so can it influence levels  of methane release by soils, furthermore. The use of reactive nitrogen in agriculture can also affect the methane released by livestock cattle in particular. These issues are outline below. The impacts of reactive nitrogen on methane maybe substantial, but the evidence is not yet clear. Owing to this uncertainty, impacts on methane where not factored into the ENA’s final figure for not nitrogen affect.

(3)        Methane from wetland’s :

It is fairly well known that wetland ecosystem/cultivation emit methane, as do wetland based agricultural systems, such as rice agriculture through methanogen bacteria, which released methane in anaerobic conditions (wetland).

Increasing availability  of reactive nitrogen to plants can result in increased photosynthesis and more carbon being sent by plants to their root systems, which ultimately becomes available to soil-based methanogen microbes that convert it to methane. However, these increased in plant productivity may dry out the soil, increasing soil oxygen levels, stimulating metabotropic microbes to oxidize more methane. The ENA concluded that whilst EV wetlands (and water bodies) emit 3.92Tg of methane carbon each year (citing sarnie et al,2009), the impact of reactive nitrogen deposition on this figure is negligible (adding just 0.01Tg of methane carbon each year).

          Recommendation for resolving the problem :

(1)        Developing in national nitrogen strategy :-

This strategy would offer important starting point to solve the problem, including setting a policy agenda, create a platform for social political debates, providing an overarching framework from political action programs; and formulating widely supported policy goals. It should be on the bars of cooperation  between various governmental and non-governmental actors .

The national nitrogen strategy  should contain the following elements;

(a)Nitrogen related objection should be bundled, and the target system further developed. This overarching target should be based on ecosystem resilience and should be supported by targets for major inputs in the agriculture, as well as for nitrogen emission in the transport and energy sectors.

(b) It should combine existing nitrogen radiation measures and regulations and should identify medium and long-term areas for action. 

Mahi Abrar a recent graduate in civil engineering from Bangladesh Army University of Engineering and Technology (BAUET), and excited to venture into the realm of environmental discourse, particularly focusing on the enigmatic realm of nitrogen dynamics. Armed with a solid educational foundation and a fervent commitment to sustainability, I aim to illuminate the intricate relationship between nitrogen, agriculture, and environmental sustainability. Through this article, I aspire to offer a comprehensive exploration of the challenges posed by reactive nitrogen, leveraging my academic background and passion for innovative problem-solving. Let us embark on this journey together as we unravel the complexities of nitrogen's impact on our planet's ecosystems and future.