Manure Management Facts Manure Nutrients And Their Behaviour In Soil

Manure Management FactsManure Nutrients and theirBehaviour in SoilJanuary 2009Manure is both a natural by-product of livestockproduction and an excellent source of nutrientsfor crop production. The use of manure as afertilizer is a beneficial way to recycle manurenutrients within an agricultural system. Mostlivestock operations are on, or surrounded by,large areas of productive agricultural land wheremanure can be applied in a sustainable manner.In many instances, manure can be a substitutefor commercial, inorganic fertilizers. Manurenot only acts as a source of plant nutrients but,through the addition of organic matter, it alsohelps to improve soil tilth, structure, aeration andwater holding capacity.There are many factors that affect the nutrientcomposition of manure including the typeof housing system, whether or not beddingis used, the type of bedding, the age of theanimals, the feeds and feed supplements thatare being used and the type of manure storageand handling system.Nitrogen in ManureThe nitrogen (N) content of manure is highlyvariable (Table 1). A manure analysis is requiredto determine how much N is in the manureand in what forms. A proper manure analysiscontains three N measurements: total nitrogen ammonia (or ammonium) nitrogen organic nitrogenAs the term suggests, total nitrogen is an estimateof all the N contained in the manure. It includesammonium N, organic N and any nitrate Nthat may be present. Not all of this N will beavailable to the crop following application.Manure as a FertilizerManure contains both macro- and micro-nutrientsneeded for crop production in organic andinorganic forms. Inorganic nutrients are readilyavailable to the growing crop, while the organicnutrients become available gradually overtime. A crop responds to inorganic nutrientsin soil, whether they originate from manure orcommercial fertilizer. The manure nutrients ofprimary interest for crop production are nitrogen(N) and phosphorus (P).Ammonium N (NH4-N) is the predominantinorganic form of N in manure and it isimmediately available to the crop followingapplication. It may be expressed as eitherammonium or ammonia on the manure analysisand it is the same form of N as is in ammoniumbased commercial fertilizers.Nitrate N (NO3-N) is another inorganic form ofN. Although soil can contain significant quantitiesof nitrate N, it is typically present in manure invery low or insignificant amounts.

Manure Application to SoilOrganic nitrogen is determined indirectly bycalculating the difference between total N andammonium N. Organic N is slowly released tothe crop and can have a significant impact on theN-supplying power of the soil if it is allowed tobuild up after several years of manure applications.When manure is applied to soil, the nutrientscan undergo a number of transformations thatmay accelerate or delay their availability forcrop uptake. The availability of the N in manureis highly variable and is influenced by the formsof N in the manure, application techniquesand timing, along with weather conditions. Theavailability of the P in manure depends on theforms of the P and its placement relative to theplant root system.Organic N Total N – Ammonium NPhosphorus in ManureThe phosphorus (P) content of the manure is alsohighly variable (Table 1). Although manure isa mixture of organic and inorganic P, manureanalyses routinely measure only total P.Table 1. Nitrogen, Phosphorus and Moisture Contents of Various Manures1TotalNitrogenManureTypeLiquid Pig2n 70Liquid Dairyn 208Liquid Chickenn 65Solid Beefn 147Solid Chickenn 5412OrganicNitrogenTotalPhosphorus--------------- lb/1000 gal trogenTotalPhosphorusDry MatterManureTypeSolid Dairyn 75AmmoniumNitrogen------------------ lb/ton 1.216MARC 2008. Manure Application Rate Calculator software for Manitoba, Manitoba Agriculture, Food and Rural InitiativesFor pig manure data by operation type with and without phytase use, see the Farm Practices Guidelines for Pig Producers in Manitoba, Manitoba Agriculture, Food and Rural Initiatives, April 2007.

VolatilizationThe ammonium N in manure can be lost tothe atmosphere as ammonia gas through thechemical process of volatilization. The amount ofN lost through volatilization during applicationof manure depends on the amount of ammoniumin the manure, exposure of the manure to theatmosphere and weather conditions (Table 2).The actual amount of ammonium available to thecrop is calculated by subtracting the amount ofammonia estimated to be lost by volatilizationduring application from the amount of ammoniumin the manure.Nitrogen Behaviour in SoilAvailable Ammonium N TotalAmmonium N x (100% - %Volatilization loss)MineralizationManagement practices that minimize N lossesdue to volatilization include:The organic N in manure must go through adecomposition process known as mineralization –the conversion of organic N to ammonium N.In Manitoba, it is estimated that about 25%of the organic N in manure is mineralizedand available to the next crop. The remainderbecomes available during subsequent years atsignificantly decreased rates. injection of manure surface application of manure with immediateincorporation; cool conditions; humid conditions (note: manure should not beapplied in wet or rainy conditions that increasethe risk of surface runoff).NitrificationAlthough nitrate is present at low concentrationsin manure, manured soils can contain significantamounts. This is because the ammonium fromthe manure is converted to nitrate by soilmicroorganisms through the nitrification process.ImmobilizationImmobilization is the conversion of inorganic Nto organic N (i.e. the opposite of mineralization).Table 2. Volatilization losses (%) associated with differentapplication methods and weather conditionsMethod of ApplicationWeather ConditionsAverageCool WetCool DryWarm WetWarm DryInjected00000Incorporated 1 day2510152550Incorporated 2 day3013193157Incorporated 3 day3515223865Incorporated 4 day4017264472Incorporated 5 day4520305080Not Incorporated66405075100IrrigatedAbove 10%Above 10%Above 10%Above 10%Above 10%Standing/Cover Crop/Stubble3525254050

DenitrificationNitrogen can be lost to the atmosphere as N2and N2O through a microbial process calleddenitrification. N2O is a potent greenhouse gas.Management practices that minimize N lossesdue to denitrification include: avoiding nutrient applications to areas of thefield that are wet such as poorly drained soilsand depressional areas late fall (when soil temperatures are below4C), spring or in-season applications ofN containing fertilizers including manure,whenever possible.Nitrate LeachingNitrate is highly soluble in water. As water movesdown through the soil, such as after snowmelt orheavy rainfall, it can carry nitrate with it. Nitratecontamination of groundwater is a concern,particularly if the groundwater is a sourceof drinking water. The guideline maximumacceptable concentration of nitrate in drinkingwater, set by Health Canada, is 10 milligramsper litre (mg/L) nitrate N (or 45 mg/L nitrate).Management practices and conditions thatminimize the risk of nitrate leaching and nitratecontamination of groundwater include: N applications that target crop N requirements annual soil testing for residual N at a depth of0-24 inches residual soil nitrate N is the concentrationof nitrate in the soil after harvest when thecrop is not actively growing adjustment of N application rates to maintainlow concentrations of residual soil nitrate N medium to fine textured soils coarse textured soils such as sands are atthe highest risk of nitrate leaching crops with dense or deep rooting systemssuch as grass and alfalfa that are efficient atintercepting and withdrawing soil nitrate N judicious irrigation to avoid excessmoisture levels deep groundwater that is protected by finetextured materials such as clay.Runoff and Soil ErosionNitrogen can be transported to surface water inrunoff water and through soil erosion. Nitrogen inthe form of ammonia is particularly toxic to fish.Management practices that minimize N losses tosurface water include: soil conservation practices to minimizesoil erosion injection and incorporation of manure,particularly fall-applied manure maintaining appropriate application setbacks.Phosphorus Behaviour in SoilAlthough P is less dynamic in soil than N, itsmanagement in manure is challenging. MostManitoba soils are naturally deficient in plantavailable P. Crops growing on low P soils requirefertilization to reach optimal yields and willbenefit from a build up in soil P until agronomicrequirements are met. However, repeatedapplications of manure can result in soil P levelswell above agronomic requirements. In additionto being a valuable crop nutrient, P is a seriouscontaminant at elevated levels in surface water.For this reason, loss of P from agricultural lands isof particular concern to surface water quality.MineralizationAs with N, mineralization of organic P toinorganic P takes place in the soil and contributesto the supply of plant available P.