Nutrient and Carbon Balance during the Composting of Deep Litter

J. agric. Engng Res. (1999) 74, 145}153Article No. jaer.1999.0446, available online at http://www.idealibrary.com on

Nutrient and Carbon Balance during the Composting of Deep Litter

S. G. Sommer; P. Dahl

Research Centre Bygholm; Danish Institute of Agricultural Sciences, Department of Agricultural Engineering; P.O. Box 536, 8700 Horsens,Denmark; e-mail: Sven G. [email protected]

(Received 11 September 1998; accepted in revised form 29 May 1999)

During the storage of solid animal manure, biological transformation of nitrogen (N) and carbon (C) mayincrease the temperature from 60 to 703C, i.e. composting. Composting may cause emission losses of ammonia(NH

3) and carbon dioxide (CO

2). Furthermore, plant nutrients may leach from the compost heaps. During

a composting period of 197 day from September 1997 to April 1998, emission of NH3, nitrous oxide (N

2O),

methane (CH4) and CO

2was measured using dynamic chambers covering three heaps of deep litter from

a house with dairy cows. Leaching of nutrients during composting was determined. Denitri"cation wasestimated as N unaccounted for in an N mass balance. The heaps were either mixed once after 30 days,compressed initially or left untreated. Compacting the heap caused a temperature increase from 10 to 50}603C.The temperature increased from 30 to 403C in the heap being mixed. From both the compacted and mixed heap,the cumulative ammonia volatilization was 0)2 kgN/t corresponding to between 2)6 and 3% of the total N. Halfof this amount was lost from the untreated heap in which the temperature only increased marginally in the "rstdays after the start of the experiment. Cumulative CO

2losses were 33 (19%), 20 (12%) and 17 kg C/t (10%) from

the litter mixed after 30 days, compressed deep litter and untreated deep litter, respectively. Emissions of N2O

and CH4

were low. Nitrogen losses due to leaching were (0)8% of the initial N. Total nitrogen losses due todenitri"cation, NH

3emission and leaching was from 5 to 19% of the initial N, the lowest from mixed and the

highest from untreated litter.( 1999 Silsoe Research Institute

1. Introduction

Solid manure amounts to about 20% of the Danishmanure (Poulsen & Kristensen, 1998). Farmyard manureconstitutes the majority of solid manure; however, anincreasing interest in loose housing systems built withsolid #oors strewn with straw for welfare reasons will infuture increase the amount of deep litter (Andersen et al.,1999). It is the policy of the Danish government that10}20% of Danish agriculture should be farmed in agree-ment with the rules for organic farming. This will contri-bute to an increased production of solid manure, asorganic farmers tend to have animals on deep litter.

During storage, 20}40% of N in deep litter may belost, mainly though gaseous emission (Karlsson & Jep-pson, 1995; Eghball et al., 1997). The Danish governmentintends to reduce the amount of N imported to farms in

0021-8634/99/100145#09 $30.00/0 14

feed and fertilizers, thus, a reduction in the loss of N fromagriculture is needed to maintain the plant production ontraditional farms. In organic farming, N is mainly pro-vided by N-"xing leguminous plants, and as large a partas possible of this N has to be transferred in manure fromthe grazed "elds to "elds in rotation. E$cient use ofmanure-N for plant production is, therefore, very impor-tant if plant production is to be maintained in bothtraditional and organic farming systems.

Composting processes and gaseous emission of oxi-dized and reduced nitrogen has been measured duringcomposting of municipal litter or livestock manure beingturned frequently, often several times each week (Hell-man et al., 1997; Martin & Dewes, 1992). However, thereare few studies of nutrient losses from deep litter duringcomposting. During storage, the deep litter will start tocompost and organic farmers will enhance the composting

5 ( 1999 Silsoe Research Institute

S. G. SOMMER; P. DAHL146

process by mixing the heap once after one month, be-cause they believe that composting improves the fertilizervalue of organic manure.

Gaseous emission of N of C and leaching losses ofN and P during composting of deep litter has beenquanti"ed in this study. A movable dynamic chamberwas used to determine gaseous losses, and liquid from thecompost was collected for the purpose of estimatingleaching losses of nutrients. Furthermore, the loss ofN caused by denitri"cation was estimated as a di!erenceby means of a mass balance. Techniques for reducing thelosses were developed and tested.

2. Material and methods

2.1. ¹reatments

Gas emission and leaching losses of nutrients weremeasured during 197 days, composting in three pilot-scale heaps of deep litter from the housing of dairy cows.The litter was stored in heaps with a length of 3)7 m,width of 1)9 m and height of 1)3 m on a sealed surface(length of 4m, width of 2 m), with collection of runo! toclosed containers buried in the soil. The amount andcomposition of the deep litter used for composting isgiven in Table 1. In the experiment from 29th September1997 to 14th April 1998, the deep litter was mixed bytreating the material three times with a manure spreaderon the "rst day of the experiment. Immediately after thistreatment, three portions of the litter were stored underthe following conditions: (1) compressed once duringstorage, (2) mixed once by turning the heap manuallyafter 30 d, and (3) untreated.

TablQuantity and composition of stored deep litter from housing of daiuntreated. Volume of the deep litter heaps being 3, 3'2 and 3'6 m

Sampling Treatment Amount,occasion t

DM Ash Ntotal

Initial Untreated 0)720 422 (1) 61 (1) 8)4 (0)3)Compressed 0)980 379 (50) 52 (6) 7)5 (1)1)Mixed 0)660 409 (11) 59 (2) 8)3 (0)1)

End Untreated 0)810 214 (9) 46 (2) 6)0 (0)2Compressed 0)990 229 (5) 55 (4) 6)5 (0)3)Mixed 0)810 202 (3) 46 (3) 6)4 (0)4)

DM, dry matter; TAN, total ammoniacal nitrogen.

2.2. Dynamic chamber

The dynamic chamber consists of a mobile chambercovering the storage during measurements, a ventilatorfor suction of air through the chamber, and equipmentfor measurement of gas, temperature and wind velocity.A "eld laboratory placed close to the experimental areaprovided the supply of electricity (340 V AC) to the venti-lators and instruments for measurement of gas emission.

The three mobile chambers on wheels had the dimen-sions: height, 1)6 m; width, 2 m; and length 4 m. Thechambers were made of marine plywood and mountedon a metal frame, with only one gable closed by plywood,the opposite end being open for facilitating the chambersto be moved over the heaps, and connected to a station-ary gable placed at the end of the sealed surface. Thegable on the chambers had an opening for incoming air.A steel tube (length of 2 m, inner diameter of 0)40 m) witha ventilator was connected to the stationary gable. A rec-tangular metal frame was mounted on the sealed surfaceperpendicular to the stationary gable. The dimensions(length of 4 m, width of 2 m) of the frame allowed it to "tclosely with the chambers when mounted. Air was drawnthrough the chamber by the ventilator, enabling mea-surements of the #ux of gases to and from the chamber.

Air#ow through the dynamic chamber was measuredwith cup anemometers in the steel pipe, the air#ow ratescould be adjusted from the "eld laboratory. Air temper-ature and the temperature 0)40 m above the bottom ofthe deep litter heap was measured with PT100 and ther-mocouple sensors (Kontram A/S, DK-Copenhagen). Thesensors were connected to a datalogger (DatatakerDT200, Data Electronics Ltd, Australia).

One-quarter of an hour before a measurement, thechambers were moved over the deep litter heap and "xed

e 1ry cows. The deep litter was compressed, mixed after 30 days and3, respectively. (Standard deviation in bracket for two samples)

Composition, g/kg

TAN NO3 P K C

0)54 (0)03) 0)20 (0)00) 1)43 (0)03) 13)5 (0)1) 177)9 (0)9)0)63 (0)04) 0)13 (0)04) 1)21 (0)20) 12)0 (1)3) 160)3 (24)2)0)60 (0)04) 0)25 (0)04) 1)40 (0)02) 13)7 (0)5) 172)4 (4)8)

0)21 (0)02) 0)00 (0)00) 1)16 (0)04) N.D. 85)98 (6)1)0)26 (0)02) 0)00 (0)00) 1)31 (0)07) N.D. 91)65 (4)3)0)23 (0)02) 0)00 (0)00) 1)17 (0)05) N.D. 79)20 (3)0)

147COMPOSTING OF DEEP LETTER

to the stationary gable. When measuring emissions ofNH

3, the wind speed was adjusted to 3 m/s; and when

measuring emission of N2O, CH

4and CO

2, the wind

speed was adjusted to 1)2 m/s. Atmospheric NH3

of air#owing into the chambers and from each chamber wasdetermined with two active denuders (Ferm, 1979) ateach sampling occasion. For the analysis of CH

4, N

2O

and CO2, four gas samples of 55 ml were taken with

syringes both at the inlet of the chamber, and from thesteel tube 30 cm from the gable on each measuring occa-sion. The samples were stored as described below for gassamples taken from the deep litter heap. The emissionwas calculated as the di!erence in the #ux between theincoming and outgoing gases. Determination of emissionwas stopped in January 1997 after 87 days, because nogas emission could be detected in January. Concentra-tions of gas in and emissions from the heaps were deter-mined twice on the "rst day, once each day from day 2to 6, twice per week from week 2 to 5, once each weekfrom week 6 to 8 and once every fortnight from week9 to 12.

2.3. Gas-phase composition

For the determination of CH4, N

2O, CO

2and oxygen

(O2) gas samples were collected from the centre of the

deep litter heaps by modifying the technique of Petersenet al. (1998). The two ends of a #exible, but rigid plastictube with an internal diameter (i.d.) of 10 mm and con-taining four holes, 2 mm in diameter, per cm length wereconnected to two 2 m lengths of gas-tight Te#on tubes(i.d. 2 mm). The Te#on tubes were connected to a dia-phragm pump (Model 5002, ASF GmbH, Germany).A silicone tube was inserted into the rigid tube, but after2}3 weeks no air samples could be collected, and on day30 the silicone tube was removed from the rigid plastictube in the heap that was mixed after 30 days. A septumfor gas sampling was located immediately after the dia-phragm pump, continuously circulating air through thetubes during an experiment. Four samples of 60 ml weretaken at each sample collection with syringes. The gassamples were transferred to 5 ml glass bottles "tted withbutyl rubber septa. When transferring a sample to the glassbottle, an extra needle was inserted through the rubber sealand the bottle was #ushed with 45 ml of the gas in thesyringe; then the needle penetrating the septum was re-moved and the 15 ml remaining in the syringe was injected.

2.4. Nutrient composition

At the initiation and the conclusion of the experiment,two samples each of 2 l of organic material were taken

from each heap. Samples of liquid (0)5 l) leaching fromthe dung heap were taken when the containers werenearly full and emptied. The samples of organic materialand liquid were stored at !183C.

Before analysis, the organic material was thawed to03C and the sample of 2 l was "nely chopped with a cut-ting machine. Representative subsamples of about 500 gof the chopped material were then cut into small piecesand from this material 100 g was taken for analysis. Allmanure samples were analysed for dry matter (DM), ashcontent, total C, Kjeldahl N (N

505!-), total ammoniacal

nitrogen (TAN), NO~3, P and K.

2.5. Analysis

2.5.1. AmmoniaThe concentration of ammonia in the air from the

background and from the dynamic chamber was deter-mined by active denuders (Ferm, 1979). An active de-nuder consists of a glass tube (length 500 mm, innerdiameter 7 mm) coated on the inside with oxalic acid,through which air is drawn at a "xed air#ow. A dia-phragm pump provides suction and a critical ori"ceadjusts the air#ow to exactly 0)9 l/min through the de-nuder. All NH

3#owing into the tube is absorbed by the

oxalic acid. After exposure, the amount of NH3absorbed

in the tubes was determined, by dissolving the coating in5 ml water and analysing NH

3concentration using

a QuickChem 4200 (Lachat Instruments WI, USA).

2.5.2. Methane, nitrous oxide, carbon dioxide and oxygenNitrous oxide and CH

4were measured on a Hewlett-

Packard (5890, series II) gas chromatograph with anelectron capture detector and a #ame ionization detector.It was equipped with a 1)8 m]3 mm column withporapak Q 80/100 for N

2O; with Ar/CH

4(95/5) used as

carrier gas at 30 ml/min; and temperatures of injectionport, oven and detection were 110, 40 and 3203C, respec-tively. Methane was isolated with a 1)8 m]3 mm columnwith poropak N 80/100; He was used as a carrier gas at30 ml/min; and temperatures of injection port, oven anddetection were 110, 40 and 2703C, respectively. Oxygenand CO

2were measured on a Varian 3350 gas chromato-

graph equipped with a thermal conductivity detector. Itwas equipped with a 1 m]3 mm column with MolecularSieve 5A 60/80 for isolating O

2and a 2 m]3 mm Haysep

R 80/100 for CO2. The carrier gas was He at a #ow rate

of 30 ml/min, and the temperatures of oven and detectorwere 30 and 1903C, respectively.

2.5.3. Nutrient compositionTotal ammoniacal nitrogen and NO~

3in the solid

manure were extracted in 1 M KCl for 30 min, "ltered


before analysis with a QuickChem 4200 #ow injectionanalyser (Lachat Instr. WI, USA). Dry matter was deter-mined after drying at 1053C for 24 h, and ash content at5503C for 4 h. Total C was determined by dry combus-tion (Leco model 521-275), K by #ame photometry(FLM3, Radiometer) after incineration and dissolving inacid, and P was measured colorimetrically (Spectronic1001, Braush & Lomb) after incineration and dissolvingin acid, and a colouring reaction with ammonium molyb-date vanadate. Total nitrogen was analysed usingthe Kjeldahl method and a Kjellfoss 16200(Copenhagen, DK). Total-nitrogen, P, K, TAN and NOv

3in the leachate from the dung heap were determinedwithout extraction.

2.6. Calculations

The average NH3

concentration Catm

in g NH3-N/m3

in the air passing through two Ferm tubes used at eachsampling occasion was calculated by the following equa-tion:

Catm

"

(C1#C

2!2C

3)<

2;D*t

(1)

where C1

and C2

are the concentrations of NH`4

ing NH

4}N/l in the leachate from the two exposed de-

nuders, C3

the average concentration of NH`4

ing NH

4}N/l in the leachate from four blank denuders,< is

the volume of water used to dissolve the NH`4

sorbed inthe denuders (0)005 l),;

Dis the air#ow through the tubes

(0)0009 m3/min), and *t is the time in minutes betweenthe start and conclusion of the measurement.

The gas emission F in g of component/day of NH3,

N2O and CO

2is calculated by the equation:

F"602]24uA (Xe!X

b) (2)

where Xeand X

bare the concentration of gases in g/m3

in air from a dynamic chamber and background air,respectively, u the air#ow in the tunnel in m/s and A thecross-sectional area of the steel duct in m2.

Total loss of DM, N an P was calculated by a massbalance [Eqn (3)]. The ash and P content were assumedto be conserved and used for correction of DM, thusproviding a basis for estimating nutrient losses duringstorage (Petersen et al., 1998; Dewes et al., 1990). Theprecision of this technique was tested by comparinglosses of dry matter F

DMin kg determined by the use of

total mass balance [(Eqn (3)] and conservation of eitherP or ash [(Eqn (4)].

FDM,2

"0)001 (DMstart

Qstart

!DMend

Qend

) (3)

FDM,3

"0)001Qstart

(DMstart

!DMend

Pstart

/Pend

) (4)

where DMstart

and DMend

are the dry matter concentra-tion in g/kg; Q

startand Q

endthe mass in kg; and P

startand

Pend

the concentration of phosphorous in g P/kg of deeplitter stored and compost at the end of the experiment,respectively. In Eqn (4), ash concentration may be usedinstead of phosphorous.

3. Results and discussion

3.1. ¹emperature and gas concentration in the compost

At the initiation of the experiments the ambient windspeed was high. Therefore, the temperature only in-creased from 20 to 303C in the heaps that were notcompressed and to 50}603C in the compressed heap(Fig. 1). The O

2concentrations inside the heaps were

almost at the same level as the concentration in theambient air (data not shown), indicating that the air#owrate through the heaps was su$cient to replenishO

2used in the aerobic metabolism of organic residues by

micro-organisms.The temperature measured during the "rst week was

related to changes in ambient wind speed and declined atwind speeds above 15 m/s. The CO

2concentration in the

compressed heap increased considerably, and the con-centration re#ected changes in the temperature of theheaps (Fig. 1). Temperature and CO

2concentrations are

related, because photosynthesis processes are negligiblein compost and CO

2, therefore, can be regarded as

a parameter for microbial activity (Knuth, 1969). Aftera few weeks, no gas could be sampled from inside theheaps, due to a reduced permeability of the silicone tubein the perforated plastic tube. The sampler in the mixedheap was changed with a plastic tube without a siliconetube when mixing the heap after 30 days. After mixingboth the temperature and CO

2concentration increased

in this heap, but a temperature increase was also mea-sured in the compressed heap (Fig. 1). The increase isprobably related to growth of actinomyces and fungiafter the temperature decline, the fungi using celluloseand hemicellulose as substrate (Hellman et al., 1997).After 50 days, the temperature in the compressed andmixed heap declined to ambient temperature and CO

2in

the mixed heap declined to ambient concentrations.The N

2O concentration in the heaps did not deviate

from the ambient concentrations apart from concentra-tions of 2)2 p.p.m. in the compressed heap on the "rst dayand concentrations of 1)1 p.p.m. after having mixed theheap. Methane concentrations were between 2 and3 p.p.m. and almost similar to the ambient concentra-tions near a dairy farm (data not shown). Nitrous oxideand CH

4concentrations were low compared with those

measured in the studies of Petersen et al. (1998) and

Fig. 1. Temperature readings (a) and CO2 concentrations (b) in three heaps of stored and composting deep litter from the housing ofdairy cows. The deep litter was treated as follows:~~K, compressed;~ ) )~s, mixed once after 30 days;~~~n , left untreated;

. . . . . , air temperature


Sibbesen and Lind (1993). The open structure of the deeplitter has facilitated a high convection of air through theorganic material, which has diluted the gases and re-duced N

2O and CH

4formation, or induced CH

4oxida-

tion.

3.2. Gaseous emissions

Emission of CO2

was high immediately after the heapswere established and in a period between 30 and 40 daysafter the initiation of the experiment. Emission of 2}3 kgCO

2-C/t per day was determined during these periods

(Fig. 2). The emission of CO2

was not detectable after 87days. The total CO

2emissions were 33, 20 and 17 kg C/t

from the litter being mixed after 30 days, compresseddeep litter and untreated deep litter, respectively. Theemission of CO

2was signi"cant and reduced the content

of C in the compost heap with 10}19% (Table 2).The highest emission of N

2O of 10 gN/t per day or

approximately 2}3 g N/m2 per day was observed 10}15days after the initiation of the experiment. In studies ofCzepiel et al. (1996) and Hellmann et al. (1997) the highestN

2O emissions were observed 30}70 days after the initia-

tion of the experiment. The di!erence in emission patternmay re#ect that the temperature in these two experimentswas high in a longer period than in the present study. Theemission was low compared with emissions from un-treated manure heaps determined by Sibbesen and Lind(1993) and Petersen et al. (1998).

Methane emission from the compressed and untreatedlitter was only observed in the period from 30 to 40 daysafter the initiation of the experiment. The highest CH

4emission measured was 40 g CH

4-C/t per day or approx-

imately 15 g CH4-C/m per day, which is similar to the

emissions determined by Husted (1994).Ammonia was only emitted from the dung heaps dur-

ing the "rst 10 days after the establishment and in themixed heap again 2}3 days after turning of the heap(Fig. 3). In a study of NH

3volatilization from pig deep

litter, Lammers et al. (1997) observed a similar pattern inemission. The volatilization of NH

3was low from the

heap of untreated litter in which there hardly was anyinitial increase in temperature, indicating that NH

3losses can be reduced by a treatment restraining thetemperature increase in deep litter during storage. Cumu-lative NH

3volatilization from the compacted and mixed

heaps was similar (Table 2). Ammonia emission duringcomposting was low compared with the losses measuredby Lammers et al. (1998), probably because immobiliz-ation in the animal house had reduced the concentrationof NH`

4of the litter stored in the heaps. Furthermore, the

litter had a high C : N ratio of 21.

3.3. Mass balance and leaching losses of nutrients

The total loss of N, C, P and DM shown in Table 3 wascalculated by the concentration of components and theamount of deep litter and compost initially and at the

Fig. 2. Emission of (a) CO2, (b) CH4 and (c) N2O during 87 daysfrom three heaps of composting deep litter from the housing ofdairy cows. The deep litter was treated as follows: ~~K , com-pressed; ~ ) )~ s, mixed once after 30 days; ~~~ n , left

untreated


end of composting using Eqn (3). For comparison thedi!erence in dry matter initially and at the end of com-posting was calculated by Eqn (4) by assuming a constantash content during composting* as proposed by Deweset al. (1990) * or a constant content of P (Table 4).Losses of dry matter calculated by assuming a constantP content was from 13% lower to 12% higher than theDM loss calculated by Eqn (3). Assuming a constant ashcontent, the DM loss was 6% lower to 25% higher thanDM losses calculated using Eqn (3), showing that the ashcontent may change during a composting period, prob-ably due to the formation of solids of calcium, carbon-aceous components and phosphorous. Thus, if theamount of stored manure is too great for being homogen-ized and weighed, then P would be more precise than theash content when calculating the losses of nutrients orcarbon assuming the content of these components to beconstant.

Reduction in the dry matter content was between 39and 40% which is similar to the "ndings of Karlsson andJeppson (1995). Most of the loss in dry matter duringcomposting can be ascribed to the emission of CO

2and

CH4, because C constitutes a substantial part of the

organic matter (Table 1) and the reduction in C contentwas between 43 and 46% of the initial C content (Table 3).The loss of C was probably caused by the emission ofCO

2as CH

4emission was low (Fig. 2). The accumulated

CO2

emission determined with the dynamic chambersaccounted only for half of the loss of C. The low recoveryis probably due to an increase in emission rates of CO

2in

the spring after the measurements were stopped in Jan-uary. While the winter rain increased the water content ofthe compost from 600 to 800 l/t, dilution by rain andemission of CO

2during the composting period halved

the concentration of DM.Leaching losses of P were less than 0)8% (Table 3) of

the initial content and, due to the small losses of P, therecoveries of P in the compost were 92}109%, which issimilar to the "ndings of Petersen et al. (1998). As a con-sequence of the low losses of P during composting anda small increase in the weight of compost, the concentra-tion of P was una!ected by composting.

Less than 0)4% of the initial N leached from thecompost. The volume of e%uent from the compactedlitter was 0)6 m3/t and from each of the two other heapswas collected 1 m3/t. As N was immobilized, the leachinglosses of N were lower than those determined by Martinand Dewes (1992) and Karlsson and Jeppsson (1995). Theconcentration of TAN in the e%uent was (0)003 g/l andthe NO~

3concentration was below the detection limit,

indicating that very little inorganic N in the deep litterwas dissolved in the rain leaching through the organicmaterial. The absence of NO~

3is in accordance with

previous observations of nutrient composition during

Table 2Cumulative emission of ammonia, carbon dioxide and nitrous oxide during 87 days of composting. After 87 days the emission was

below the detection limit of the measuring technique

Treatment Ammonia Carbon dioxide Nitrous oxide

kg N/t % Ntotal kg C/t % C g N/t % Ntotal

( fresh weight) ( fresh weight) (fresh weight)

Untreated 0)1 1)2 17)1 10 0)388 0)0005Compressed 0)23 3)0 19)7 12 0)17 0)0002Mixed 0)22 2)6 32)9 19 0)04 0)00005

N505!-

, total N.


composting of animal manure (Eghball et al., 1997; Peter-sen et al., 1998).

According to the mass balance N losses due to leach-ing, NH

3emission and denitri"cation were between

5 and 19% of the initial N. The N loss was low from themixed manure and high from the untreated manure.These losses are smaller than the losses determined frompig solid manure or cattle manure (Petersen et al., 1998),probably because the C :N ratio of the latter was between8 and 10, which is much lower than the C : N ratio of 20 inthis study. It has been shown by Kirchmann (1985) thatan increase in C : N ratio signi"cantly reduces N lossesduring storage and composting of livestock solid manure.Mixing the heap after 30 days increased microbial activ-ity and may have enhanced immobilization of N, thereby,reducing the total loss of N compared to the untreated

Fig. 3. Ammonia loss rate (a) and cumulative ammonia volatilizationdairy cows. The deep litter was treated as follows:~~h , compresse

heap. The amount of N unaccounted for in the massbalance was between 1)9 and 14)2% of the initial N. TheN unaccounted for may have been lost through denitri"-cation; the losses were lower than the denitri"cationlosses of 13}33% observed by Petersen et al. (1998). Thehigh porosity of deep litter reduces the sites with anaer-obic conditions and immobilization may have competedwith denitri"cation reducing the amount of NO~

3present

in the compost.

4. Conclusion

The immobilization of N caused by a high C :N ratioin deep litter reduces the content of inorganic N duringstorage of the litter. Consequently, leaching losses of

(b) from three heaps of composting deep litter from the housing ofd;~ ) )~s , mixed once after 30 days;~~~ n, left untreated

Table 3Changes in mass balance of nutrients during composting of deep litter from September 1997 to April 1998 during a period of 197 days,negative values indicate an increase in nutrients or C and positive values the loss of nutrients or C (values in parentheses are pool sizes

in % of the nutrient or C at start). Gas emission was measured for 87 days

Treatment Method of estimation N,kg N/t

P,kg P/t

C,kg C/t

Dry matter,kg DM/t

Untreated Di!erence* 1)6 (19) 0)1 (8) 81 (46) 182 (43)Gas emission 0)1 (1)2) 0 (0) 17 (10)Leaching 0)03 (0)4) 0)01 (0)7) N.D.Unaccounted 1)47 (14)2) 0)09 (6)3) 64 (36)

Compressed Di!erence* 0)9 (12) !0)11 (!10) 68 (43) 148 (39)Gas emission 0)23 (3)0) 0 (0) 20 (12)

Leaching 0)03 (0)3) 0)01 (0)8) N.D.Unaccounted 0)64 (8)7) !0)12 (!10)8) 48 (31)

Mixed Di!erence* 0)4 (5) !0)03 (2) 75 (44) 161 (39)Gas emission 0)22 (2)7) 0 (0) 32 (19)

Leaching 0)03 (0)4) 0)01 (0)7) N.D.Unaccounted 1)15 (1)9) !0)01 (!2)7) 43 (25)

*Di!erence in the amount of components in the deep litter before and after composting; DM, dry matter.


nitrogen are very low ((0)5%) and gaseous emissions ofNH

3and N

2are lower than those from solid manure.

Reducing the period with composting and high temper-ature and mixing the deep litter once during storagereduced the gaseous emission of N in this study. Drymatter loss during eight months of storage was between39 and 43%, most of this loss was caused by transforma-tion of organic C to CO

2and the emission of the latter.

Emission of the greenhouse gases N2O and CH

4was

low, and leaching losses of total N, NO~3, NH`

4and P

negligible.

Table 4Dry matter lost during composting of deep litter from September1997 to April 1998, calculated by Eqn (3) using the measuredquantity of deep litter and DM concentration initially and at theend of the storage period; and by Eqn (4) assuming that thecontent of either ash or phosphorous in the deep litter initially aresimilar to the content in the compost after the storage period

Treatment Loss of dry matter, kg DM/t (% of initial amount)

By weight By ash By phosphorousconcentration concentration

Untreated 181 136 159Compressed 148 166 167Mixed 160 146 165

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Nutrient and Carbon Balance during the Composting of Deep Litter