Perspectives for Agronomy

T. Morvan , ... B. Mary , in Developments in Crop Science, 1997

two.3 Analytical procedures

Inorganic nitrogen in the soil was adamant in a KCl extract (600 ml 1 M KCl/300 g fresh soil, shaken for 30 min, and then filtered through a Whatmann 42 filter), using the fractionated steam distillation with MgO for ammonium and Dewarda's alloy for nitrate analysis ( Drouineau and Gouny, 1947). Organic plus clay-fixed nitrogen and l5N was measured on a sample of moist soil, afterwards removal of the inorganic nitrogen, every bit described by Recous et al., 1988; the sample was dried at 60°C, and finely basis.

Atom backlog was determined on subsamples of plant, soil, and dried solutions resulting from the steam distillations, using a full combustion technique linked to a VG SIRA 9 mass spectrometer (Recous et al., 1988).

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Transformations of nitrogen

David D. Myrold , in Principles and Applications of Soil Microbiology (Third Edition), 2021

Inorganic nitrogen fertilizers are the most widely used tool to manage crop nitrogen fertility, particularly in intensively managed agricultural and forested production systems. Fifty-fifty with organic nitrogen amendments, such as manure, it is commonly causeless that the organic nitrogen must first exist converted into inorganic nitrogen before plants can utilize it. Yet, the ability of plants to take upwards organic nitrogen compounds, specially amino acids, has been known for more a century. Recently, there has been renewed interest in organic nitrogen in establish diet ( Näsholm et al., 1998), particularly plants with roots colonized by sure types of mycorrhizal fungi (Chapter 12). Much of the virtually readily available organic nitrogen is likely found in soluble, small-scale organic molecules, which make upwardly the dissolved organic nitrogen (DON) pool. Although the size of the DON puddle is typically smaller than the inorganic nitrogen in the soil solution of agricultural soils, DON can be the dominant course of soluble nitrogen in soils receiving low inputs of nitrogen. Studies in unpolluted forest ecosystems show that DON tin can exist the major form of nitrogen lost to ground and surface waters (Perakis and Hedin, 2002). Equally a result of these contempo findings, more attention is being paid to DON and its role in the nitrogen cycle.

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Hydrazine

C.E. Lambert , in Encyclopedia of Toxicology (Tertiary Edition), 2014

Background

Hydrazine is an inorganic nitrogen compound, which is an intermediate in the anaerobic oxidation of ammonia. It is produced naturally by some yeasts and the open ocean bacterium Candidatus Brocadia anammoxidans. Hydrazine plays a key role in many organic syntheses, often in those of practical significance in pharmaceuticals and pesticides, equally well as in material dyes and photography. For most uses, hydrazine is utilized as the hydrazine hydrate in a formulation with water. The hydrate is produced commercially primarily by the ketazine process, which is a variation of the original Raschig process developed in 1907. In this process ammonia is oxidized past chlorine or chloramine in the presence of an aliphatic ketone, usually acetone. The resulting ketazine is then hydrolyzed to hydrazine.

Hydrazine is highly combustible and anhydrous hydrazine fuel – produced by dehydration of the hydrate – is the formulation used in rockets. Some satellites also employ anhydrous hydrazine as a fuel source and this has become an issue of concern equally older satellites take lost their orbit and crashed or been destroyed at low altitude. Studies of the toxicology and fate and transport of inorganic hydrazine have focused on the anhydrous, hydrate, and sulfate forms, and these are the studies summarized in this article.

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Simulation Modeling: Applications in Cropping Systems

South. Asseng , ... D. Cammarano , in Encyclopedia of Agriculture and Food Systems, 2014

Nitrate Leaching

Groundwater pollution acquired by excessive inorganic nitrogen (N) fertilization is a widespread ecology problem in many agricultural systems. North in the form of nitrate (NO3 −) is very mobile in the soil and tin easily leach with moving water. Rainfall or irrigation tin cause meaning amounts of N leaching if large amounts of nitrate are present in the soil. North leaching tin besides crusade soil acidification, another potential soil degradation that limits crop growth. As a result, regulators are attempting to restrict excess nitrate in soils. For example, the European Spousal relationship (EU) Nitrates Directive (91/676/EEC) aims to preserve groundwater quality past promoting farming practices that increment N utilize efficiency of cropping systems (Basso et al., 2010). Crop models take played a role in determining crop management and its impact on externalities, such equally North leaching. For case, Asseng et al. (1998) used a crop model to show that on sandy soils and high rainfall, about of the initial soil N is lost to leaching before roots tin take it upward. Basso et al. (2012) used a crop model in a field written report and showed that less N fertilizer can be used to reduce Northward leaching without causing reductions in economic return from the ingather. Giola et al. (2012) quantified the nitrate leaching caused by mineral and organic fertilizer applications over 2 years of a maize-triticale rotation at a site in Italy with the SALUS model. The model showed nitrate leaching from slurry and manure was significantly reduced when applied without boosted mineral N applications.

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Nitrogen, Sulfur, Phosphorus, and Other Nutrients

Walter 1000. Dodds , Matt R. Whiles , in Freshwater Environmental (Third Edition), 2020

Summary

1.

The major forms of inorganic nitrogen are N 2 gas, nitrate, nitrite, and ammonium. Organic nitrogen occurs in many forms, including amino acids, proteins, nucleic acids, nucleotides, and urea.

two.

The major fluxes in the nitrogen bicycle include denitrification (using nitrate to oxidize organic C, yielding N2), oxidation of ammonium to nitrate past chemosynthetic leaner, assimilation of ammonium, fixation of N2 by bacteria, and excretion of ammonium past heterotrophs.

iii.

Forms of inorganic sulfur include sulfide, thiosulfate, sulfate, elemental sulfur, and metal sulfides. Organic sulfur is office of proteins and amino acids.

4.

The most important fluxes in the sulfur bike are biological and abiological sulfur oxidation, biological sulfur reduction (a course of anoxic respiration), product of sulfide by fermentation, disproportionation, and metal pyrite atmospheric precipitation and deposition.

v.

Phosphorus is a key chemical element that determines the productivity of many aquatic ecosystems and occurs equally phosphate and organic phosphate. Phosphatase enzymes tin can carve organic phosphorus to phosphate. Phosphate forms a low-solubility precipitate with ferric iron in the presence of Otwo that can cause its removal from oxic environments.

vi.

Silicon is a vital component of the cell walls of diatoms and tin can be a key factor in controlling composition of phytoplankton communities. It is redissolved slowly; thus, when frustules sink out of the photic zone in lakes, it takes months for the silicon to go available over again. Nether some weather condition, frustules accumulate over fourth dimension and form silica-rich sedimentary stone.

vii.

Atomic number 26 occurs as ferric and ferrous ions in oxic and anoxic habitats, respectively. It can also occur as a metal pyrite (FeS) in anoxic habitats and a flocculent precipitate [Fe(OH)3] in oxic habitats. Atomic number 26 is an important component of many proteins, including those for electron transport, nitrate assimilation, and chlorophyll synthesis.

8.

Bacteria in oxic environments can oxidize ferrous fe. Ferric iron combines with OH− or PO iv 3 − to form low-solubility precipitates. Chelators can proceed ferric iron in solution (prevent it from precipitating with OH−). Chelators are organic molecules that form complexes with fe.

9.

Gradients of redox that occur in natural waters allow for complex populations of microbes that are capable of a wide variety of nutrient transformations in localized hot spots. There is a anticipated order in which each procedure will occur across the redox slope, given the relative potential energy of each chemical reaction at each redox signal.

x.

Nutrient cycles do not occur in isolation. Complex interactions occur amidst all of them, in function because organisms have similar nutrient requirements. Interactions besides occur because unlike chemicals interact with each other in the absence of organisms.

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Nitrogen☆⁎⁎⁎

Robert Due west. Howarth , in Reference Module in Earth Systems and Ecology Sciences, 2021

Forms and transformations of nitrogen

Nitrogen occurs as both organic and inorganic nitrogen in aquatic ecosystems. Ofttimes, the organic forms boss, including both particulate organic nitrogen (PON) and dissolved organic nitrogen (DON). The PON not only includes the nitrogen in living organisms, but also big amounts of nitrogen in detritus or dead organic affair. The DON consists of a wide range of organic substances, including unproblematic substances such equally free amino acids. Much of the DON, nonetheless, consists of higher molecular weight compounds. Most of the DON in natural waters has never been chemically characterized at the level of individual compounds because of the analytical challenge of measuring thousands of unknown substances, each often nowadays at relatively low concentrations.

The inorganic nitrogen in aquatic ecosystems includes dissolved N2 gas, oxidized ions such as nitrate (NOiii −) and nitrite (NOii −), the reduced ammonium ion (NH4 +), and the reduced ammonia gas (NH3). Nitrate is the nearly oxidized form of nitrogen (valence state of +   five), while ammonia and ammonium are about reduced (valence country of −   3). Ammonium is a weak acid that in solution is in equilibrium with ammonia gas, which is a base. The equilibrium constant for this human relationship is 10–nine.3. Thus, ammonium is more ascendant whenever the pH is less than 9.3, as is almost always the case in aquatic ecosystems. At pH   =   8.3, the ammonium concentration is 10-fold greater than the ammonia concentration. At pH   =   vii.iii, the ammonium concentration is 100-fold greater than the ammonia concentration. Since ammonia is a gas, information technology can be volatilized to the atmosphere. The rate of loss is a role of the ammonia concentration, and then this process is much greater at higher pHs, where higher concentrations of ammonia are favored.

The vast majority of the nitrogen on the Globe is present equally N2 gas. This becomes biologically bachelor only through bacterial nitrogen fixation, fixation by lightning or volcanic activity, or fixation past human being activity. Before the industrial revolution, bacterial nitrogen fixation was past far the major mechanism for the creation of reactive, biologically available forms of nitrogen on the planet. Increasingly, homo activity is fixing nitrogen, and this now exceeds the natural biological nitrogen fixation globally and dominates the nitrogen wheel in many regions, as discussed below.

The primary forms of reactive nitrogen assimilated by algae, rooted plants, fungi, and bacteria are nitrate, nitrite, ammonium, and ammonia. Once taken upwards, nitrate and nitrite are reduced to ammonium in processes called assimilatory nitrate or nitrite reduction. Ammonium – whether taken upwards direct or formed by assimilatory reduction in the organism – is used by plants, algae, and microorganisms to produce organic nitrogen compounds. The organic nitrogen of plants, algae, and microorganisms can flow through a food web to animals, and detrital PON and DON is decomposed by leaner and fungi. The organic nitrogen eaten by animals or decomposed past microorganisms is excreted as ammonium or sometimes equally urea, a low-molecular weight compound that is quickly hydrolyzed to ammonium in water. These processes of releasing nitrogen back to the surroundings are called nitrogen mineralization (Fig. 1).

Fig. 1

Fig. 1. Simplified diagram of the nitrogen cycle in aquatic ecosystems.

The forms of inorganic, reactive nitrogen are converted from i to another in aquatic ecosystems through a diversity of bacterially mediated processes. Ammonium is oxidized to nitrate in a procedure called nitrification, an energy-yielding process. The nitrifying leaner that catalyze the reaction gain energy and use this energy to fix carbon dioxide into new bacterial biomass, a process called chemosynthesis. The energy yield of the reaction is depression compared with many chemosynthetic processes based on oxidizing sulfur or iron compounds, and and then the growth of nitrifying bacteria is irksome. Nitrification rates are in function a function of the population size of nitrifying bacteria; where mortality on the leaner is loftier due to grazing, the tiresome growth result keeps population sizes low, and rates of nitrification can be very low, allowing ammonium to accumulate.

Nitrate is reduced to nitrite and nitrite is reduced to Ntwo in a procedure called denitrification, also called dissimilatory nitrate reduction. The bacteria that catalyze these reactions are heterotrophic bacteria that gain their energy from the degradation or organic matter; they utilise the nitrate or nitrite as an electron acceptor, very much as plants and animals and many other microorganisms use oxygen as an electron acceptor for respiration. Since the energy yield of respiring organic matter using nitrate as the electron acceptor is somewhat less than when using oxygen every bit the electron acceptor, denitrification tends to occur only when oxygen is absent-minded or present at very low levels. This is often the instance in aquatic sediments, and often in the bottom waters of stratified lakes and estuaries. Denitrification is the major sink for reactive nitrogen in natural ecosystems. At the global calibration, denitrification serves to residual nitrogen fixation and maintains N2 gas as the major grade of nitrogen on the planet.

Many of these nitrogen-bike processes have been understood in broad brush since the early years of the 20th century, but other nitrogen processes have been discovered simply in the by thirty–40   years. One of these is denitrification based on chemosynthetic oxidation of sulfide or reduced iron rather than respiration of organic matter. Another is the anaerobic oxidation of ammonium to Ntwo (ANAMOX), which is also a chemosynthetic process. And a tertiary is the dissimilatory reduction of nitrate to ammonium (DNRA). The DNRA process is a form of respiration, with organic matter being consumed using nitrate every bit the electron acceptor; however, the nitrogen is reduced to ammonium rather than to N2. Unlike denitrification, DNRA conserves the nitrogen in the ecosystem in a reactive, biologically available grade. The controls that may make denitrification or DNRA more important in any particular situation remain imperfectly known, just evidence suggests that DNRA may dominate in sediments that are more reducing and have higher concentrations of dissolved sulfides (Burgen and Hamilton, 2007).

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Nitrogen-Utilize Efficiency Under Changing Climatic Atmospheric condition

Amitav Bhattacharya , in Changing Climate and Resources Utilise Efficiency in Plants, 2019

iv.3.2 Nitrogen Assimilatory Enzymes

Nitrates are the predominant grade of inorganic nitrogen in agricultural soils and are, therefore, used by many plant species. Nitrates enter root cells where they are either stored in a vacuole or reduced and incorporated into amino acids. Nitrogen assimilatory enzymes, which are linked to this nitrogen uptake process in roots, include nitrate reductase (NR), nitrite reductase (NiR), and the glutamine synthetase (GS)/glutamine-two-oxo-glutamate aminotransferase (GOGAT) pathway. NO 3 − that enters the cell can be reduced by nitrate reductase to nitrite. Nitrates are toxic in cell cytosol and are rapidly transported to plastids for further reduction to ammonium by nitrite reductase. Generated ammonium then enters the glutamine synthetase and glutamate synthesis cycle, where it is converted into glutamine and glutamate (Oaks, 1994; Lam et al., 1996). Ammonium present in cytosol can be assimilated directly to glutamine via glutamine synthetase activeness and then used in a series of transamination reactions to produce amino acids. Moreover, NH iv + is constantly beingness produced in leaf mitochondria during the photorespiratory nitrogen cycle. This NH 4 + pool is reassimilated by glutamine synthetase in the chloroplast or by glutamate dehydrogenase (master root for ammonia assimilation in plants) activity in the mitochondria (Cuturier et al., 2007). These reactions are regulated by the GS/GOGAT pathway active in chloroplast or cytosol of constitute cells. In leaves, these interactions are at the expense of primary products of photosynthesis and they compete with the reduction of carbon. In roots, stored or translocated carbohydrates are the primary substrate for carbon and energy requirement of nitrogen assimilation (Fig. iv.3). Therefore, nitrogen assimilation seems to exist different in roots and shoots (Oakes and Hirel, 1985). A hypothesis that glutamate dehydrogenase plays an important role in controlling glutamate homeostasis has been put forward. This function, which may have a signaling role at the interface of carbon and nitrogen metabolism, may exist of importance under certain phases of institute growth and development when in that location is an important release or accumulation of ammonia (Terce-Laforgue et al., 2004). Moreover, the major catalytic activity for glutamate dehydrogenase in plant cells has been reported to be glutame deamination (Masclaux-Daubresse et al., 2006; Purnell and Botella, 2007) and glutamate dehydrogenase activity was shown to be essential for plant survival in nighttime weather condition (Miyashita and Adept, 2008).

Figure 4.three. Main reactions involved in nitrogen assimilation in higher plants. NO 3 − = nitrate; NO 2 − = nitrite; NH 4 + = ammonium; North2 = atmospheric dinitogen; NR = nitrate reductase; NiR = nitrite reductase; Nase = nitrogenase; GS = glutamine synthetase; GOGAT = glutamate synthase. Carbon originating from photosynthesis through the tricarboxylic acid wheel (TCA cycle) provides the α-ketoglutarate needed for the reaction catalyzed by the enzyme GOGAT. Amino acids are further used for the synthesis of proteins, nucleotides, and all nitrogen-containing molecules.

 Adopted from Hirel et al. (2011).

Nitrogen is mostly taken upwards during the vegetative phase of crop growth. Nitrogen applied early in the season stimulates vegetative growth (tillering or branching), while nitrogen applied late in the season has a greater influence on the terminal nitrogen concentration in the grain (Lütke Entrup and Oemichen, 2000). College nitrogen-use efficiency can be plant when nitrogen is applied late (at flowering) than when it is applied early in the season (Raun and Johnson, 1999; Cassman et al., 2002). Nitrogen fertilizer rates and types and awarding times influence nitrogen indices such as nitrogen uptake (Iqbal et al., 2005), and its translocation within the plant (Kichey et al., 2007). Thus, fertilizer application timing has a meaning function in determining the quantity of uptake and its utilise past plants (Limaux et al., 1999). Nitrogen in aboveground parts is actively recycled and transported to grain as the constitute matures (Cooper et al., 1986). The redistribution of nitrogen from aboveground found parts to grains has been broadly studied (Van Sanford and MacKown, 1987; Feller and Fischer, 1994; Fangmeier et al., 1999; Masclaux et al., 2001). The flow and amount of nitrogen redistributed to developing seeds will vary depending on the source–sink ratio, which is regulated past the weather (temperature, drought, etc.) and the inherent properties of the organs (Dalling et al., 1976). Information technology has been suggested that remobilization of nitrogen from roots may play an important role in the final nitrogen economic science of the whole plant (Dalling et al., 1976; Simpson et al., 1983). Roots accept been suggested to play a major office in nitrogen assimilation when the ingather is suffering nitrogen deficiency in the shoots (Vouillot and Dervienne-Barret, 1999) that is followed on the remobilization of nitrogen to grains during the grain filling period.

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NITROGEN IN SOILS | Nitrates

D.S. Powlson , T.M. Addiscott , in Encyclopedia of Soils in the Environment, 2005

Conclusions

Nitrate is the most common form of inorganic nitrogen in soil, beingness the concluding production of the decomposition of organic materials nether aerobic conditions. It is the form normally taken up by plants, though most plants can also accept upward ammonium. If sufficient food is to exist grown for the current globe population of over six billion and its expected growth during the xx-start century, greatly increased amounts of nitrogen will exist needed. Information technology will be necessary to employ increasing amounts of inorganic fertilizers in improver to improve utilization of organic manures and other wastes and comeback in the use of legumes to supply nitrogen to crops. This continued intensification of agriculture will inevitably lead to further losses of nitrate to natural waters. The considerable amount of research conducted over recent decades can help to decrease these losses, both by increasing the efficiency of utilise of inorganic fertilizers and by amend retaining nitrate from organic matter mineralization within the soil/plant arrangement. However, losses tin never be entirely eliminated as the nitrate ion is soluble and is ever at some risk of being done out of soil. Information technology can also be converted to nitrous oxide, a powerful greenhouse gas. The ecological impacts of nitrate on aquatic ecosystems tin be serious so, for a range of environmental reasons, information technology is important to minimize nitrate losses from agricultural soils equally much as possible. This is in addition to the economic and sustainability reasons for fugitive waste matter of a vital resource. All the same, the proposed adverse health impacts of nitrate in water that have been the main driver for limiting nitrate loss now appear to be unfounded. Indeed, the reverse appears to exist the case – there is prove from medical research that some intake of nitrate has beneficial effects on health through the production of nitric oxide in the stomach and its part in the control of gastroenteritis.

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