Nitrogen Fertilizer Quizlet Contributes To Acid Rain
- November 19, 2021
Point-source pollution is easy to identify.The United States Environmental Protection Agency (EPA) defines point source pollution as any contaminant that enters the environment from an easily identified and confined place.Factories and power plants can be a source of point-source pollution, affecting both air and water.Effluent from a treatment plant can introduce nutrients and harmful microbes into waterways.It is a big problem in cities because of all the hard surfaces, including streets and roofs. .
Fertilizers and Soil Acidity
- Of all the major fertilizer nutrients, nitrogen is the main nutrient affecting soil pH , and soils can become more acidic or more alkaline depending on the type of nitrogen fertilizer used.- Nitrate-based products are the least acidifying of the nitrogen fertilizers, while ammonium-based products have the greatest potential to acidify soil.- Soil acidification due to use of phosphorus fertilizers is small compared to that attributed to nitrogen, due to the lower amounts of this nutrient used and the lower acidification per kg phosphorus.- Potassium fertilizers have little or no effect on soil pH .Soil acidification is a widespread natural phenomenon in regions with medium to high rainfall, and agricultural production systems can accelerate soil acidification processes through perturbation of the natural cycles of nitrogen (N), phosphorus (P) and sulfur (S) in soil, through removal of agricultural produce from the land, and through addition of fertilizers and soil amendments that can either acidify soil or make it more alkaline (Kennedy 1986).Nitrogen can be added to soils in many forms, but the predominant forms of fertilizer N used are urea (CO(NH₂)₂), monoammonium phosphate (NH₄H₂PO₄), diammonium phosphate ((NH₄)₂HPO₄), ammonium nitrate (NH₄NO₃), calcium ammonium nitrate (CaCO₃+NH₄(NO₃)) ammonium sulfate ((NH₄)₂SO₄), urea ammonium nitrate (a mixture of urea and ammonium nitrate) and ammonium polyphosphate ([NH₄PO₃]n).The conversion of N from one form to the other involves the generation or consumption of acidity, , and the uptake of urea, ammonium or nitrate by plants will also affect acidity of soil (Figure 1).It can be seen in Figure 1 that ammonium-based fertilizers will acidify soil as they generate two H⁺ ions for each ammonium molecule nitrified to nitrate.The form of P fertilizer added to soil can affect soil acidity, principally through the release or gain of H⁺ ions by the phosphate molecule depending on soil pH (Figure 2).The form of P in diammonium phosphate (DAP) is HPO₄²⁻ which can make acidic soils ( pH <7.2) more alkaline but has no effect on soil with a pH >7.2.Soil acidity and P fertilizers. .
The Role of Soil pH in Plant Nutrition and Soil Remediation
For instance, soil pH is controlled by the leaching of basic cations such as Ca, Mg, K, and Na far beyond their release from weathered minerals, leaving H+ and Al3+ ions to dominant exchangeable cations; the dissolution of CO 2 in soil water producing carbonic acid, which dissociates and releases H+ ions; humic residues from the humification of soil organic matter, which produces high-density carboxyl and phenolic groups that dissociate to release H+ ions; nitrification of to produces H+ ions; removal of N in plant and animal products; and inputs from acid rain and N uptake by plants .For many decades, intensive research has revealed that soil pH influences many biogeochemical processes.This has implications for nutrient recycling and availability for crop production, distribution of harmful substances in the environment, and their removal or translocation.Simultaneously, in accordance with biochemical changes, physicochemical processes, including dissolution, precipitation, adsorption, dilution, volatilization, and others, influence leachate quality .Soil pH controls the solubility, mobility, and bioavailability of trace elements, which determine their translocation in plants .Additionally, the quantity of dissolved organic carbon, which also influences the availability of trace elements, is controlled by soil pH.For instance, Bradl  found that at pH 5.3, the adsorption of Cd, Cu, and Zn onto a sediment composite consisting of Al-, Fe-, and Si-oxides was 60%, 62%, and 53%, respectively.Any increase or decrease in soil pH produces distinct effects on metal solubility.In contrast, Förster  found that a decrease in soil pH by one unit resulted in a ten-fold increase in metal solubility.In an experiment, he observed that at pH 7, only about 1 mg Zn·L−1 of the 1200 mg·kg−1 total Zn content was present in soil solution.Aside from adsorption, trace element concentrations at high soil pH may also be caused by precipitation with carbonates, chlorides, hydroxides, phosphate, and sulphates [11, 16].Apatite and lime applied to soils produced the highest effect on pH and simultaneously decreased the concentrations of available, leachable, and bioaccessible Cu and Cd .Soil organic matter exists in different fractions ranging from simple molecules such as amino acids, monomeric sugars, etc.The solubility and mobility of the fractions differ during and after decomposition and could lead to the leaching of dissolved organic carbon and nitrogen in some soils.Within the pH condition in a specific soil system, the solubility of organic matter is strongly influenced by the type of base and is particularly greater in the presence of monovalent cations than with multivalent ones .It is estimated using the metabolic quotient ( q CO 2 ) as an index  to show the efficiency of organic substrate utilization by soil microbes in specific conditions .It is observed from the literature that soil pH conditions required for microbial activity range from 5.5–8.8 [26, 31, 32].Stursova and Walker  found that organophosphorus hydrolase has optimal activity at higher pH.For instance, glycosidases have an optimal pH range between 4 and 6 compared to proteolytic and oxidative enzymes whose optima was between 7 and 9 [35, 36, 38].Shifts in microbial community composition could potentially influence enzyme production if different microbial groups require lower nutrient concentrations to construct biomass, or have enzymes which differ in affinity for nutrients .Biodegradation is the chemical dissolution of organic and inorganic pollutants by microorganisms or biological agents [34, 40].The biodegradation process rather slowed down in three acidic United Kingdom soils (pH 4.7 to 6.7) in 90 days after inoculation .Xu  found some strains of bacteria isolated from petroleum-contaminated soil in northern China being able to degrade over 70% of petroleum at pH 7 and 9.This also has implications for the functions of extracellular enzymes that aid in the microbial transformation of organic substrates.Additionally, at a higher soil pH, the mineralizable fractions of C and N increase because the bond between organic constituents and clays is broken .The volatilization of ammonia is a phenomenon that occurs naturally in all soils  and has been attributed to the dissociation of to NH 3 and H+ shown in equation (1) .The rate of acidification depends on the initial and final concentrations of ammonium as well as on the buffering capacity of the medium .This can either occur through the direct effect of biochemical processes occurring in the living organisms in the soil system, mostly through rhizosphere processes or through the direct and indirect effects of applied organic residues, whether in unburnt, burnt, or charred forms as well as their decomposition.Therefore, rhizosphere pH could increase or decrease depending on the prevailing process and types of ions released.Plant root-induced soil pH change in the rhizosphere is controlled by specific processes and factors such as (i) ion uptake coupled with the release of inorganic ions that maintain electroneutrality, (ii) the excretion of organic acid anions, (iii) root exudation and respiration, (iv) redox-coupled processes, (v) microbial production of acids after the assimilation of released root carbon, and (vi) plant genotype [58, 59].The dominant mechanism responsible for pH changes in the rhizosphere is plant uptake of nutrients in the form of cations and anions [58, 59, 65], primarily due to plant uptake of the two major forms of inorganic nitrogen ( and ), which is usually taken up in large quantities .The uptake of each of the three forms of nitrogen accompanies the release of corresponding ions to maintain electroneutrality in the rhizosphere.In contrast, protons are released by plants in response to uptake, causing a decrease in rhizosphere pH [58, 62].The extent of effects of the processes and factors controlling rhizosphere pH change depends on plant species and growth stages .Maize initially acidified the rhizosphere and gradually alkalized it over time while beans showed opposite effects.This was revealed in an experiment on apple trees (Malus pumila Miller), buckwheat (Fagopyrum esculentum Moench), corn (Zea mays L.), cowpeas (Vigna unguiculata (L) Walp.L.), and wheat (Triticum aestivum L.), where Metzger  found maximum concentrations of in the rhizosphere during the blooming and fruiting stages (Figure 2), which was 10–29% higher compared to the bulk soil.The concentrations of in the rhizosphere of the plants was in the order, lettuce = buckwheat > pine > apple > kaffir > cowpeas > corn > wheat.When unburnt organic materials or raw plant residues are applied to the soil, the pH increases to a peak and decrease afterwards.For instance, Forján et al.  found initial increases in soil pH when they applied a mixture of sludge from a bleach plant, urban solid waste and mine wastes, and a mixture of sludge from a purification plant, wood chips, and remnants from agri-food industries to the soil.Furthermore, in a 59-day laboratory incubation  and field experiments , it was found that the magnitude of soil pH increase following residue amendment was in the order chickpea > canola > wheat [71, 74].They observed that 40–62% of soluble alkalinity in canola and chickpea residues were responsible for the pH increases.It is obvious from these, and many other studies , that the residues of dicots, particularly legumes, have high alkalinity and produce larger effects on soil pH change than monocots.The pH increase after residue addition often reaches a peak and declines thereafter as a result of nitrification.Similar to unburnt organic materials, burnt or charred plant residues contain a larger amount of alkalinity due to the volatilization of organic constituents under thermal conditions leading to the concentration of alkaline constituents.The actual alkalinity depends on the type of biomass involved, their origin, and burnt temperature.Biochar is a solid consistent product pyrolysis, while ash is a loose powdery material obtained by combustion.Biomass ash contains substantial alkalinity, which is often expressed as percent calcium carbonate equivalence (% CCE).The mobility of unwholesome substances through the hydrological cycle cannot be overlooked here because of the intimate relationship between soil and water.These, as well as pH maxima for various microbial enzymes, could be utilized in many soil remediation strategies, particularly in bioremediation.
c. Cellular respiration is an important metabolic process that moves phosphorous from the atmosphere into living organisms in the phosphorus cycle.It is one of the elements essential to life and is quickly excreted by animals, which therefore require a continual phosphate intake from their food.Phosphate is returned to the soil in animal and plant wastes (feces, dead material).A proportion of the phosphate returned the soil is washed into watercourses and thus into the sea, where it may become trapped in ocean bottom sediments.