Manure Management Technology Development Team East National Technology Support Center Manure Chemistry – Nitrogen, Phosphorus, & Carbon

August 2007 Manure Management Information Sheet Number 7

INTRODUCTION and moves rapidly in runoff and in soil solutions. Buildup of nitrate in groundwater is a health It’s hard to talk about manure management without concern; the concentration limit in drinking water is referring to the complex chemistry involved. It’s 10 mg per liter. While in surface waters the also hard to remember all that stuff we learned so concentration is rarely that high, nitrogen still long ago--- especially when somebody starts contributes to eutrophication (excess plant growth). throwing around words like ‘anoxic,’ Excessive use of nitrogen fertilizers is implicated in ‘mineralization,’ and ‘redox.’ This document is the expansion of a hypoxic area or “Dead Zone” in intended to provide a compact overview of what the Gulf of Mexico. happens to three critical elements—nitrogen, The ammonia form of nitrogen can be an air quality phosphorus, and carbon—during manure storage concern. Manure nitrogen is often converted into and treatment. the ammonium (soluble) form by bacteria. If the NITROGEN pH is above neutral, the manure is warm, and there is nothing to work against ammonification, the The element nitrogen (N) has many oxidation states ammonium changes into the ammonia (gaseous) and can form numerous compounds. Elemental N2, form and volatilizes into the atmosphere. Ammonia or diatomic nitrogen, composes 78% of the air we in significant concentrations is harmful to livestock breathe, and nitrogenous compounds are and agricultural workers; it is also a precursor to components of all living tissue. In manure, N harmful particulates and facilitates the formation of occurs as nearly all of these forms at one time or undesirable gases. another: There are five natural processes that transform N Nitrogen Formula Oxidation from one form to another: Fixation, Species State ammonification, synthesis, nitrification, and Organic nitrogen Org-N denitrification. Ammonia, NH3 -3 Ammonium ion NH + -3 • Fixation: the conversion of nitrogen gas [N2] 4 from the atmosphere into any form of nitrogen Hydrazine N H 2 4 -2 used by plants and animals. The most familiar Hydroxylamine NH2OH -1 example is the work done by Rhizobia bacteria Nitrogen gas N2 0 attached to the roots of legumes, which can

reduce N2 from the atmosphere into NH3. A Nitrous oxide N2O +1 certain amount of N2 is also transformed into NO by lightening and delivered to the soil in Nitric oxide 3 NO +2 rain. Plants utilize N as either ammonium (from

bacteria) or nitrate (from bacteria, lightening, or Nitrous acid HNO +3 2 fertilizer). Animals get their N by eating plants Nitrite ion - NO2 +3 or other animals. Nitrogen dioxide NO +4 2 • Ammonification: the degradation of organic-N to Nitric acid HNO3 +5 ammonium, usually by bacteria. This can - Nitrate ion NO3 +5 happen under both aerobic and anaerobic conditions if the appropriate bacteria are present. Nitrogen is of concern to agriculture both as an essential plant nutrient for building proteins and • Nitrification: converting ammonium to nitrite and amino acids and as a potential water pollutant. then nitrate, in a type of biological oxidation. The two bacterial species Nitrobacter and Nitrogen, as nitrate or ammonium, is highly soluble

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Nitrosomonas are most commonly associated to NO3 is interrupted or slowed by lack of with this transformation. oxygen, the intermediate NH3 will be driven off. • Synthesis: the biochemical mechanism that • Anaerobic digestion: Passing through a digester converts ammonium or nitrate into living cells, has little effect on the total nitrogen content of either plant cells or bacterial cells. (Animals manure. A negligible amount of N may be cannot eat straight ammonium or nitrate and emitted as NH3, but the majority will be found convert it.) as organic N and NH4 in solution in the digester sludge. The ammonium content of digester • Denitrification: The completion of the nitrogen sludge will be higher than that of raw manure. cycle by returning N to the atmosphere as N2 Although the anaerobic conditions should favor gas. Denitrifying bacteria convert NO3 to N2 production of ammonia, the ammonium is held under anoxic (low oxygen) conditions. This can in solution by the pressurization of the vessel, occur in soils that undergo periods of and the slightly acidic pH favorable to saturation, either naturally or under cultivation methanogenic bacteria. as in rice production. • Gasification: a portion of the N in manure will be After manure is excreted, the organic nitrogen, gasified into either N2 or N2O. This process is ammonium, and urea in the feces and urine are still poorly understood and may be highly subjected to treatment and storage. Urea is quickly variable depending on conditions. The ash and converted to ammonium. Here are some of the char remaining after gasification is usually low transformations that might occur, depending on in nitrogen. how the manure is handled: • Pyrolysis: Some N will be found in the oil • Storage: What happens to nitrogen in structures products, where it is considered a contaminant. designed to store, rather than treat, manure The remaining N is usually found in solution in depends on whether conditions are aerobic the watery waste remaining after the oils have (plenty of oxygen) or anaerobic (no free been distilled off. oxygen.) In aerobic conditions, the N will • Composting: A portion of the N in the compost largely remain in the manure as organic N or pile is volatilized as NH , and a small amount ammonium. Aerobic conditions may exist in dry 3 may be emitted as N O. The remainder is stack storage, poultry litter storage, or systems 2 found either in the bodies of microorganisms as specifically designed to aerate the manure. In organic N, or as NO , which is available to anaerobic conditions, which usually apply, a 3 plants. portion of N will probably be lost to the atmosphere as NH3. • Land application: Raw (untreated) manure applied to land contains nitrogen in the form of • Anaerobic lagoons: Structures specifically organic compounds and ammonium. Dryer designed as anaerobic lagoons are not just for manure from feedlots and poultry litter will also storage. In a properly operating lagoon, contain some nitrate-N. The organic nitrogen in conditions foster anaerobic decomposition. pH manure is broken down into forms plants can will be at or above neutral, in contrast to absorb over time. Nitrate is highly mobile in soil storage facilities which are more acidic. solution, as is ammonium to a lesser degree. Manure has a long residence time in most Both are readily used by crop plants. anaerobic lagoons, allowing for complex Unfortunately, they are also mobile in surface chemical and biological interactions. Nitrogen runoff, and may cause water pollution if not will be converted into NH and NH by biological 4 3 properly managed. Manure management activity. When conditions favor ammonia calculations generally assume that most volatilization, NH will be lost to the 3 available nitrogen in manure will be utilized by atmosphere. Ammonification is accelerated by plants or denitrified by soil microorganisms in high pH and warmth. three years. When land applied, manure can • Aerobic lagoons: Under aerobic conditions, also lose nitrogen as ammonia through where oxygen is freely available, far less volatilization. This occurs during application and ammonia is generated than in anaerobic as the manure sits on the soil surface. conditions. In these situations, N will be Incorporation or injection reduces these losses, retained in solution as NO3 and NH4, and in the because the ammonium will be nitrified by soil bodies of aerobic microorganisms as organic N. bacteria. In wet soils and under appropriate Nitrogen converted to ammonium will be conditions, anaerobic bacteria may then mineralized as NO3. If the conversion from NH4 denitrify the nitrate and give off nitrogen gas.

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PHOSPHORUS Under acidic anaerobic conditions, P can form the gas phosphine (PH3). However, rather than Phosphorus is a non-metal found in the same volatilizing like ammonia, phosphine usually chemical family as nitrogen. The most common recombines with other constituents of the manure oxidation states found in nature are +3, +5, and -3. and is not lost. Phosphorus generally forms compounds with oxygen, hydrogen, and halides [e.g. fluoride]. In Note that in treatments that reduce the mass of the agriculture, we’re most familiar with it in fertilizer manure, like composting, gasification, pyrolysis, compounds such as mono- and di-ammonium and digestion, the concentration of P increases phosphate, triple super-phosphate, and as the because it does not go away. plant-available ion in soils, orthophosphate (H2PO4- • Storage: When manure is stored as a solid, not ). Regardless of the actual chemical form of the much happens to the phosphorus; it will still be phosphorus, the analyses of phosphorus fertilizers present as it was when stored. When stored as are given as phosphate (P2O5). a liquid, the P tends to accumulate in the sludge at the bottom of the storage unit, as organic P Phosphorus (P) is an essential nutrient for both present in the bodies of microorganisms. plants and animals. All DNA molecules contain phosphorus. Plants need it for flowering and • Anaerobic digestion: Digestion has little effect on P, other than moving some of the dissolved reproduction, as well as energy exchange. Animals portion into the bodies of bacteria that carry out need phosphorus for a number of processes the anaerobic digestion process. All of the P including energy processes, formation of bone, and present in the manure will still be present in the building eggshells. digester sludge. In manure, P is present in organic matter and as • Gasification: Since P is not a component of any dissolved reactive phosphorus—DRP or of the gases produced in this process, all the P orthophosphate. The dissolved form is easily present in the manure at the beginning of the transported from crop fields to surface water in process will still be there at the end, contained runoff, where it can cause nutrient imbalances in the ash and char residuals. leading to eutrophication and other water quality • Pyrolysis: As with gasification, all of the P will problems. end up in char and other residuals. Because P does not easily form gases, it stays in the • Composting: At the end of the composting manure through storage and treatment. Organic process, most of the P will be in organic form, phosphorus is contained in the bodies of contained in live or dead microorganism bodies. microorganisms in the manure. Dissolved reactive All of the initial P will still be present. P in solution can be coagulated with metal • Land application: Ideally, all the P in land- compounds and then aggregated into clumps that applied manure would be taken up by crop will settle out by treating the manure with plants. In reality, some is transported in runoff, flocculating polymers. Solids separation some moves into the soil profile, and some is technology may partition up to 90% of P into the bound by metal ions (calcium, aluminum, and solid portion of the manure if the separation process iron.) Soils have varied capacity for binding P, is augmented with coagulants and flocculants. depending on pH, cation exchange capacity, Solids separation without chemical assistance may rainfall, type of clay present, and presence of metals (primarily aluminum and iron oxides.) remove anywhere from a few percent of total P up Over time, all the easily available P in the root to 60%, depending on how efficiently the method zone will be used by crops as long as the separates out fine manure particles, where most of amount of manure applied is in balance with the P is contained. crop needs. In many parts of the country, Under certain conditions, (pH between 7 and 11 and excess manure has been applied for years and soils are heavily loaded with phosphorus that is a sufficient amount of dissolved magnesium) P can slowly traveling down the soil profile, and may combine with magnesium and ammonium to form never be fully utilized. the crystalline compound struvite [magnesium ammonium phosphate hexahydrate, CARBON MgNH4PO4·6H2O]. Forced precipitation of struvite has been investigated as a way of removing P from The abundant carbon atom is present in all forms of manure effluent. terrestrial life. Carbon cycles through the soil,

3 oceans, atmosphere, earth’s geology, and living produced in the interior of particles where there things, entering into more chemical compounds is little oxygen. So much carbon is consumed than any other element. that the mass may shrink by 50% or more. • Land application: The transformation of carbon- Plants fix carbon from carbon dioxide (CO2) in the atmosphere, converting most of it into sugars and containing compounds is similar to the composting process but takes place more starches. Animals eat the plants and convert the slowly and without the increase in temperature. carbon into animal tissue. The carbon in manure Organisms in the soil mineralize carbon in comes from plant (and some animal) materials in manure into CO2, which is given off into the livestock feed. A portion of the carbon consumed is atmosphere or retained in soil gasses. Some of exhaled as methane (CH4), and of course, animals the carbon is bound into the soil as humic acid breathe in oxygen and exhale CO2. (soil organic matter.) If the ratio of carbon to nitrogen is high—for example, if the manure A large amount of the organic matter in manure is contains a lot of sawdust or other bedding, or actually the bodies of bacteria from the animal’s there is a large amount of residue on the soil gut, along with some partly digested feed. Carbon surface— the available nitrogen in the soil may is present in proteins, fatty acids, lipids, be immobilized by bacteria decomposing the carbohydrates, cellulose, and lignins. carbonaceous material, leaving plants with less nitrogen than they need for successful crop During storage and treatment, much of the carbon production. High-carbon manures, including in manure may be mineralized into CO2 or poultry litter and horse manure, benefit from converted to CH4. composting before being land applied for this reason. • Storage: Biological activity continues in the manure during storage. If the conditions are ADDITIONAL INFORMATION aerobic, CO2 will be given off, and if anaerobic, CH4 and smaller amounts of CO2 will be The fate of crop nutrients during digestion of swine emitted. When manure is stored in anaerobic manure in psychrophilic anaerobic sequencing batch lagoons, significant amounts of carbon are lost reactors. D.I. Massé, F. Croteaua and L. Massea, as methane. Bioresource Technology Vol 98, Issue 15, November 2006 • Anaerobic digestion: Simple sugars, volatile fatty acids, and alcohols degrade quickly – The Fate of Nutrients and Pathogens During Anaerobic within hours–and are converted into CH4 and Digestion of Dairy Manure. Patrick Topper, Robert CO2 with traces of hydrogen sulfide [H2S] and Graves, Thomas Richard, Penn State Agricultural and water vapor. If the residence time is long Biological Engineering Cooperative Extension enough, hemicellulose, fat, and protein will Publication G-71 June 2006 degrade in a few days. Cellulose and lignin are Livestock and Poultry Environmental Stewardship usually left intact. The gasses given off by the (LPES) Curriculum, Lesson 25, Manure Treatment digester will contain 40% to 70% methane. Options. [All of the LPES series are worth studying.] • Gasification: Under low-oxygen conditions and Can be downloaded at high temperatures, carbon compounds are http://www.lpes.org/les_plans.html converted into combustible gasses, leaving Evaluation of On-Farm Composting of Turkey Brooder behind mineral ash. The gasses contain CO, Litter. John Chastain, P. Andrew Rollins, Kathy Moore, CO , CH , C H , N , and H . 2 4 2 4 2 2 ASAE Paper # 054064, July 2005

• Pyrolysis: Manure is converted under high The U.S. Department of Agriculture (USDA) prohibits discrimination temperatures, pressure, and absence of oxygen in all its programs and activities on the basis of race, color, national into oil, char, and waste gasses. Carbon origin, age, disability, and where applicable, sex, marital status, familial monoxide (CO) is actually pumped into the status, parental status, religion, sexual orientation, genetic information, political beliefs, reprisal, or because all or a part of an individual’s process to scavenge free oxygen, and the income is derived from any public assistance program. (Not all carbon in the manure is transformed into prohibited bases apply to all programs.) Persons with disabilities who burnable hydrocarbons similar to light crude oil. require alternative means for communication of program information This process is a variant of the methods used to (Braille, large print, audiotape, etc.) should contact USDA’s TARGET Center at (202) 720–2600 (voice and TDD). To file a complaint of make charcoal from wood. discrimination, write to USDA, Director, Office of Civil Rights, 1400 Independence Avenue, SW., Washington, DC 20250–9410, or call • Composting: Carbon-containing compounds are (800) 795–3272 (voice) or (202) 720–6382 (TDD). USDA is an equal attacked by bacteria, actinomycetes, and fungi opportunity provider and employer. under aerobic conditions, and the carbon is primarily mineralized into CO2. Some CH4 is 4