TECHNICAL REPORTS

2322

Storage of cattle slurry leads to emissions of methane (CH4),

nitrous oxide (N2O), ammonia (NH

3), and carbon dioxide

(CO2). On dairy farms, winter is the most critical period in

terms of slurry storage due to cattle housing and slurry fi eld application prohibition. Slurry treatment by separation results in reduced slurry dry matter content and has considerable potential to reduce gaseous emissions. Th erefore, the effi ciency of slurry separation in reducing gaseous emissions during winter storage was investigated in a laboratory study. Four slurry fractions were obtained: a solid and a liquid fraction by screw press separation (SPS) and a supernatant and a sediment fraction by chemically enhanced settling of the liquid fraction. Untreated slurry and the separated fractions were stored in plastic barrels for 48 d under winter conditions, and gaseous emissions were measured. Screw press separation resulted in an increase of CO

2 (650%) and N

2O (1240%) emissions due to

high releases observed from the solid fraction, but this increase was tempered by using the combined separation process (CSP). Th e CSP resulted in a reduction of CH

4 emissions (≈ 50%),

even though high emissions of CH4 (46% of soluble C) were

observed from the solid fraction during the fi rst 6 d of storage. Screw press separation increased NH

3 emissions by 35%, but

this was reduced to 15% using the CSP. During winter storage greenhouse gas emissions from all treatments were mainly in the form of CH

4 and were reduced by 30 and 40% using SPS

and CSP, respectively.

Eff ect of Cattle Slurry Separation on Greenhouse Gas and Ammonia Emissions

during Storage

David Fangueiro* Instituto Superior de Agronomia

Joao Coutinho Universidade de Trás-os-Montes e Alto Douro

David Chadwick North Wyke Research

Nuno Moreira and Henrique Trindade Universidade de Trás-os-Montes e Alto Douro

Dairy farming activities pose serious environmental

problems, particularly due to slurry management,

which may lead to water contamination by nitrate (NO3) and

phosphorus and to atmospheric pollution. Agricultural activities

contribute signifi cantly to global greenhouse gas (GHG)

emissions, namely methane (CH4) and nitrous oxide (N

2O),

which are two important GHGs contributing to global warming

(IPCC, 2001), as well as carbon dioxide (CO2) and ammonia

(NH3). Ammonia is not considered to be a direct GHG but

contributes to global warming because deposited NH3 may be

converted to N2O in the soil after nitrifi cation and subsequent

denitrifi cation (IPCC, 1996).

Cattle slurry and farmyard manure are materials rich in organic

matter and nutrients, which undergo degradation and may lead

to GHG and NH3 emissions during the diff erent management

stages. Many studies have been performed to quantify GHG and

NH3 emissions that occur during or after application to land

(Genermont et al., 1998; Chadwick et al., 2000; van Groenigen et

al., 2004; Rochette et al., 2004). Other studies have proposed and

tested solutions to decrease such emissions (Mattila, 1998; Flessa

and Beese, 2000; Sommer and Hutchings, 2001; Wulf et al.,

2002a, 2002b; Peräla et al., 2006; Rhode et al., 2006).

However, land application is the last stage of slurry or manure

handling, and research has also focused on gaseous emissions

from stored slurry or farmyard manure (Chadwick, 2005; Mis-

selbrook et al., 2005) or has considered both stages, storage and

soil application (Amon et al., 2001; Amon et al., 2006). Th ese

authors showed that signifi cant emissions occur during storage

and that eff ective decreases of gaseous emissions may be achieved

at this stage of slurry management.

In dairy systems that combine grazing and housing, cows are

generally housed during winter; consequently, slurry is mainly col-

lected and stored during this period. In systems with no grazing,

Abbreviations: DM, dry matter; GHG, greenhouse gases; PAM, polyacrylamide; PAM-sup,

PAM-supernatant fraction; PAM-sed, PAM-sediment fraction; TGA, trace gas analyzer.

D. Fangueiro, Instituto Superior de Agronomia, UIQA, TU Lisbon, Tapada da Ajuda,

1349-017– Lisboa, Portugal. J. Coutinho, Chemistry Centre, Dep. of Soil Science,

Universidade de Trás-os-Montes e Alto Douro, Apartado 1013, 5001-801 Vila Real,

Portugal. D. Chadwick, North Wyke Research, Okehampton EX20 2SB, UK. N. Moreira

and H. Trindade, Centre for the Research and Technology of Agro-Environment and

Biological Sciences, Dep. of Plant Science and Agricultural Engineering, Universidade

de Trás-os-Montes e Alto Douro, Apartado 1013, 5001-801 Vila Real, Portugal.

Copyright © 2008 by the American Society of Agronomy, Crop Science

Society of America, and Soil Science Society of America. All rights

reserved. No part of this periodical may be reproduced or transmitted

in any form or by any means, electronic or mechanical, including pho-

tocopying, recording, or any information storage and retrieval system,

without permission in writing from the publisher.

Published in J. Environ. Qual. 37:2322–2331 (2008).

doi:10.2134/jeq2007.0330

Received 21 June 2007.

*Corresponding author (dfangueiro@isa.utl.pt).

© ASA, CSSA, SSSA

677 S. Segoe Rd., Madison, WI 53711 USA

TECHNICAL REPORTS: WASTE MANAGEMENT

Fangueiro et al.: Gaseous Emissions from Storage of Treated Cattle Slurry 2323

slurry is collected and stored throughout the year, but restrictions

on slurry application to fi elds is only of major concern during

the winter (November–March). Hence, it is during winter that

farmers have more problems related to slurry storage. Slurry

separation is one solution proposed to farmers to increase storage

capacity and improve slurry handling. Mechanical separation of

solids from slurry results in two fractions: a liquid slurry frac-

tion with low dry matter content and a solid fraction. However,

organic forms of nutrients (N and P) in slurry are mainly found

in small suspended particles, which are not removed by mechani-

cal separation (Vanotti et al., 2002). To achieve a more effi cient

separation, the liquid fraction obtained by mechanical separation

can be treated with a fl occulating agent, such as polyacrylamide

(PAM) or bentonite, to produce, by chemically enhanced set-

tling, a supernatant and a sediment fraction (Vanotti and Hunt,

1999; Vanotti et al., 2002). Polyacrylamide may also be added to

untreated slurry before screw press separation. However, addition

of PAM to a slurry pit before solids removal can result in large

amounts of sediment in the bottom of the slurry store, which can

be diffi cult to remove by pumping. In contrast, PAM application

to the separated liquid fraction generates less sediment, which

can be removed by pumping. Another benefi t of using PAM af-

ter screw press separation is that the solid fraction obtained in the

fi rst step may be composted and the fraction of supernatant ob-

tained after PAM addition may be used as a fertilizer. Screw press

separation can result in a reduction of about 50% of the dry mat-

ter content from the untreated slurry, and values of 70% can be

reached by combining mechanical and PAM treatment (Pereira

et al., 2005). Furthermore, slurry separation may help to reduce

GHG emissions during storage because separated fractions of

slurry have distinct compositions, and many authors (Chadwick

et al., 2000; Sommer and Hutchings, 2001) have shown that gas-

eous emissions depend on the slurry or farmyard manure com-

position. Recently, Amon et al. (2006) analyzed the eff ect of the

most common slurry treatment options on gaseous (NH3, N

2O,

and CH4) emissions during storage and showed that mechanical

slurry separation has some positive and negative impacts on the

environment. In their study, Amon et al. (2006) did not consider

the second separation stage (i.e., fl occulation).

In our study, slurry was treated by a combined process

that used a screw-press separation followed by chemically en-

hanced settling with PAM to obtain four diff erent slurry frac-

tions. Th e aim of this study was to estimate CH4, CO

2, N

2O,

and NH3 emissions from treated and untreated slurry during

winter storage to assess the effi ciency of such treatments in

reducing gaseous emissions during slurry storage.

Materials and Methods

Slurry TreatmentCattle slurry was obtained from an intensive dairy farm

in northwest Portugal, more details of which can be found in

Fangueiro et al. (2008c). Cows were predominantly fed with

maize silage and concentrate feed. Th e untreated slurry was fi rst

subjected to mechanical separation with a screw press separa-

tor (FAN model S650; BAUER GmbH, Voitsberg, Austria)

generating a solid and a liquid fraction. Th e liquid fraction

was subjected to chemically enhanced settling that resulted in

two more fractions: a supernatant (PAM-sup) and a sediment

(PAM-sed) fraction after the addition of 200 mg L−1 (0.02%)

of a fl occulating agent, the cationic polyacrylamide (VTA F 94)

(Vanotti et al., 2002). Th is treatment was performed at 12°C in

a 1000-L container fi lled with the liquid fraction and the PAM.

After 20 h, the PAM-sup fraction was carefully pumped from

the 1000-L container used for the separation to another 1000-L

container, and the volume of this fraction and the sediment

fraction (PAM-sed) was recorded. Subsamples of each fraction

were collected after careful stirring and then frozen before fur-

ther analyses. Mechanical (screw-press) and chemical (PAM)

separation took place 48 and 24 h before the beginning of the

storage experiment, respectively.

Experimental Facilities and Storage ConditionsTh e experiment took place in a closed building between

January and March 2006 with air temperatures maintained

below 15°C to simulate slurry storage conditions during the

winter in Portugal. Th e effl uents (untreated slurry, solid, liq-

uid, PAM-sup, and PAM-sed fractions) were stored in plastic

barrels (125-L capacity), which were 1 m deep and had a

diameter of 0.4 m. One hundred liters of the slurry fractions

or untreated slurry were stored in each barrel. Each fraction

was studied in triplicate, leading to a total of 15 plastic bar-

rels stored together under the same conditions. For the solid

fraction, barrels were insulated using a thermal material (rock

wool) to avoid heat loss through the barrel walls and to main-

tain the temperature inside the barrel high enough to promote

the natural composting of the solid fraction of slurry. Th e

temperatures of two replicates of each treatment and of the

ambient air were measured continuously using temperature

sensors connected to a data-logger.

During the experiment, the solid fraction was mixed three

times on Days 13, 19, and 29 to homogenize the material.

Because the study related to manure storage and not to com-

posting, it was not necessary to turn for the fi rst time early

after the start of storage when microbial activity was high and

required high oxygen supply. To achieve this mixing, the bar-

rels were sealed with their lids and then turned over from end

to end repeatedly for 10 min. After turning, the lids were re-

moved for a few minutes to observe the eff ects of mixing. On

Day 29, all the liquid fractions were mixed using a mechanical

agitator to simulate the slurry mixing performed periodically

at the farm-scale before application.

Gas MeasurementsEach barrel was closed at the beginning of the experiment,

leaving an open headspace between the surface of the slurry

fraction and the barrel lid of 30 L. Four air inlets were posi-

tioned symmetrically in the barrel lid (Fig. 1), and a vacuum

air pump was used to draw air through the headspace of the

barrels at a continuous and homogeneous airfl ow rate of about

3 L min−1. Th e air fl ow was controlled using fl ow meters

equipped with needle valves (model GD 100; KDG–Mobrey,

2324 Journal of Environmental Quality • Volume 37 • November–December 2008

Crawley, West Sussex, UK). Th e total volume of air fl owing

through each barrel was measured using gas meters (model

Gallus 2000 G1.6; Schlumberger Industries, Reims, France).

One air outlet, positioned in the center of each barrel lid, was

connected to an acid trap fi lled with orthophosphoric acid at

0.002 mol L−1 to trap the NH3 in the air fl ow from the outlet.

Because the air outlet was located in the center of the barrel lid

and air fl ow was forced by using an air pump connected to the

air output, air sampling was representative of the atmosphere

inside the barrel. Another acid trap connected to a gas meter

was used to measure the NH3 in the air fl ow from the inlet (Fig.

1). Th e period of time that the airfl ow passed through the acid

traps was recorded, and the NH3 trapped by the acid was quan-

tifi ed by determination of the NH4+ concentration in the solu-

tion by automated segmented-fl ow spectrophotometric meth-

ods (Houba et al., 1994). Ammonia emissions were measured

24 h d−1 for the fi rst 12 d and then 8 h d−1 for the next 36 d to

estimate the daily fl uxes. Th e CH4, CO

2, and N

2O concentra-

tions were measured directly through a sampling port located

at the beginning of the air outlet and inlet (Fig. 1) using a trace

gas analyzer (TGA) (1412 Photoacoustic Field Gas-Monitor;

Innova AirTech Instruments, Ballerup, Denmark) (Yamulki

and Jarvis, 1999). Th e TGA, fi tted with internal fi lters for par-

ticles and water and with optical fi lters for N2O (fi lter type UA

0985), CO2 (UA 0982), and CH

4 (UA 0969) was run manu-

ally in a mode including corrections for cross-interferences be-

tween CO2 and N

2O and between CH

4 and N

2O (Yamulki and

Jarvis, 1999). Previous published studies (Dinuccio et al., 2008;

Fangueiro et al., 2008b) were performed using the same equip-

ment, and no problem with cross sensitivities was reported. Th e

TGA detection limits for N2O, CH

4, and CO

2 were 0.03, 0.40,

and 1.50 ppm, respectively. Th e equipment was calibrated for

the three gases by the manufacturer 1 mo before the beginning

of the experiment, and its repeatability was 1% of the measured

value. Th e CH4, CO

2, and N

2O concentrations in the airfl ows

were measured every 4 h during the fi rst 3 d, every 6 h from

Day 4 to 8, and twice a day for the remaining days.

Net total emissions of GHGs expressed as CO2 equivalents

were estimated from the CH4 and N

2O emissions using con-

version factors of 310 and 21 for N2O and CH

4, respectively

(IPCC/OECD/IEA, 1997).

Th e sum of gas losses observed from each slurry fraction

was compared with those released from the untreated slurry

to estimate the infl uence of slurry separation treatments on

gaseous emissions. Th e sum of losses was calculated taking

into account the proportion of each fraction relative to the

untreated slurry and using the following formula:

GLT = (GL

1 × Q

1) + (GL

2 × Q

2) + … + (GL

n × Q

n)

where GLT is the sum of gas losses from the individual fractions

(kg C ton−1 or g N ton−1), GLn is the gas loss observed from

fraction n (kg C ton−1 or g N ton−1), and Qn is the proportion

of fraction n relative to the untreated slurry (%).

Chemical Composition of the Effl uentsTh e untreated slurry and the slurry fractions were charac-

terized at the beginning and at the end of the storage period

in terms of dry matter (DM), pH, total C, total N, NO3, am-

monium, and water-soluble C contents.

Statistical AnalysisTh e net cumulative fl uxes of NH

3, N

2O, CO

2, and CH

4

from each effl uent were calculated by averaging the fl ux

between two sampling points and multiplying by the time

interval between sampling points. Th e individual fl ux rates

and cumulative emissions values for each effl uent and for each

sampling occasion were arithmetically meaned to produce

averages and standard errors (SE) calculated as:

SDSE

n=

Fig. 1. Schematic representation of the system used for gas measurement.

Fangueiro et al.: Gaseous Emissions from Storage of Treated Cattle Slurry 2325

where SD is the standard deviation of n replicates. Statistical

analyses were conducted using the software package STATIS-

TIX, version 7.0 (Statistix, 2000). Results were analyzed by

ANOVA (by date) to test the eff ects of slurry treatment. To

determine the statistical signifi cance of the mean diff erences,

LSD tests were performed based on a t test. Th e level of sig-

nifi cance was set at P < 0.05.

Results

Characteristics of the Treated and Untreated SlurryTh e temperature inside the barrels followed the ambient air

temperature throughout the experiment in all treatments except

for the solid fraction (Fig. 2). In this case, temperatures were

signifi cantly higher during the fi rst 40 d of the experiment due

to the natural composting process of the solid fraction.

Th e initial composition of the untreated slurry or each slurry

fraction used in this storage experiment varied widely from one

to another (Table 1). Th e highest and lowest values of DM were

found in the solid fraction and PAM-sup fraction, respectively,

whereas the DM content was similar for all other effl uents. For

most of the analyzed parameters, contents were related to DM

content and decreased in the following order: solid fraction >

untreated slurry > liquid ≈ PAM-sed > PAM-sup. After 48 d of

storage, there was no signifi cant change (P > 0.05) in the fi nal

effl uent composition in terms of DM, total C, water-soluble C,

and total N content, except in the solid fraction. Th e DM and

total C content of the solid fraction decreased by approximately

35% and the total N content by approximately 10% during the

storage period. Th is signifi cant decrease of DM refl ected the

natural composting that occurred during the 48 d of the experi-

ment. Similar values of DM decrease were observed during

storage of cattle farmyard manure (Chadwick, 2005) and fresh

manure (Moller et al., 2002).

At the beginning of the experiment, all mineral N was

in the NH4

+ form in all treatments and represented 65% of

total N in the PAM-sup fraction, compared with 19% in the

solid fraction and about 50% in the other fractions. Some

variations of the NH4

+ contents were observed in all slurry

fractions during storage. However, these variations probably

refl ect the inherent diffi culties in uniformly sampling the

diff erent fractions, except in the solid fraction, where an ap-

proximately 90% decrease in NH4

+ content was observed.

Chadwick (2005) also measured signifi cant reductions in the

NH4

+ content of farmyard manures during storage. In the

present study, this signifi cant reduction in the NH4+ content

was probably due to N immobilization because the solid frac-

tion had C/N ratio equal to 29.6.

Fig. 2. Average temperature of the ambient air and each slurry treatment (n = 2). Standard errors removed for clarity. Arrows indicate days when mixing took place in the solid faction treatment (Days 13, 19, and 29) and stirring in all other treatments (Day 29 only).

Table 1. Characteristics of the untreated slurry and slurry fractions at the beginning and end of the experiment. Mean and SEM (n = 3) are given. Data expressed on a fresh weight basis.

Untreated slurry Solid fraction Liquid fraction PAM-sed† PAM-sup

Start End Start End Start End Start End Start End

Total C, g kg−1 27.6 ± 0.9 27.6 ± 1.0 138.9 ± 0.2 92.0 ± 0.1 19.1 ± 0.3 18.4 ± 0.4 19.7 ± 1.0 19.1 ± 0.3 5.1 ± 0.3 6.8 ± 0.6

Total N, g kg−1 2.6 ± 0.1 2.8 ± 0.0 4.7 ± 0.2 4.1 ± 0.0 2.5 ± 0.0 2.6 ± 0.1 2.7 ± 0.0 2.7 ± 0.1 1.4 ± 0.0 1.4 ± 0.1

C/N 10.7 ± 0.3 9.7 ± 0.4 29.6 ± 1.1 22.7 ± 0.9 7.6 ± 0.1 7.0 ± 0.8 7.4 ± 0.1 7.0 ± 0.2 3.6 ± 0.1 4.9 ± 0.7

NH4

+–N, g kg−1 1.3 ± 0.0 1.5 ± 0.0 0.9 ± 0.0 0.1 ± 0.0 1.2 ± 0.0 1.5 ± 0.0 1.2 ± 0.1 1.5 ± 0.0 0.9 ± 0.0 1.1 ± 0.1

NO3

−–N, g kg−1 <d.l.‡ <d.l. <d.l. <d.l. <d.l. <d.l. <d.l. <d.l. <d.l. <d.l.

Water-soluble C, g kg−1 4.1 ± 0.2 4.2 ± 0.3 1.6 ± 0.0 1.5 ± 0.0 3.5 ± 0.3 3.9 ± 0.2 2.8 ± 0.5 3.7 ± 0.3 2.4 ± 0.2 2.6 ± 0.2

Dry matter, % 6.3 ± 0.1 6.2 ± 0.1 28.2 ± 0.2 18.5 ± 0.9 4.5 ± 0.1 4.4 ± 0.1 4.6 ± 0.1 4.6 ± 0.0 1.4 ± 0.1 1.7 ± 0.1

pH 7.9 ± 0.1 7.6 ± 0.2 7.7 ± 0.1 7.8 ± 0.1 7.9 ± 0.1 7.8 ± 0.2 7.7 ± 0.1 7.5 ± 0.1 7.9 ± 0.3 7.8 ± 0.1

† PAM-sed, polyacrylamide-sediment fraction; PAM-sup, polyacrylamide-supernatant fraction.

‡ Lower than the detection limit.

2326 Journal of Environmental Quality • Volume 37 • November–December 2008

Th e NO3 content of all treatments remained negligible

during the experiment. Th is was because, despite not mea-

suring the oxygen concentration of the treatments, it can

be assumed that the untreated slurry, liquid, PAM-sed, and

PAM-sup fractions remained anaerobic. In the case of the

solid fraction, most of the material would have remained in

anaerobic conditions, although the turning process and con-

tinuous air fl ow may have created some aerobic areas.

Carbon EmissionsTh roughout the experiment, the CO

2 emission rates from

the solid fraction treatment, with values between 5.4 and

58.9 g C ton−1 h−1 (fresh weight basis), were signifi cantly

higher (P < 0.05) than from all other treatments where values

remained <1.1 g C ton−1 h−1 (Fig. 3A). Furthermore, after Day

3, CO2 emission rates were not statistically diff erent between

all treatments except the solid fraction (P > 0.05). Signifi cant

variations in CO2 emission rates were observed from all treat-

ments during the experiment, and, generally, the CO2 emis-

sion rates and the temperature followed a similar pattern (Fig.

2). A signifi cant correlation between these two parameters was

observed in the untreated slurry (r2 = 0.73; P < 0.05), in the

solid fraction (r2 = 0.63; P < 0.05), and in the liquid fraction

(r2 = 0.51; P < 0.05).

After 48 d of storage, the greatest cumulative CO2 emission was

observed from the solid fraction (Table 2). Th e values of cumula-

tive CO2 emissions were not statistically diff erent (P > 0.05) be-

tween the untreated slurry, the liquid, and the PAM-sed fractions

and were higher than from the PAM-sup treatment. However,

considering the percentage of the initial total C lost by CO2 emis-

sion, it appears that the PAM-sup fraction led to higher C losses

than the untreated slurry, the liquid fraction, or the PAM-sed

fraction. Nevertheless, the highest losses were observed from the

solid fraction (representing 18% of the initial total C content). As a

proportion of the water-soluble C, CO2 emissions represented be-

tween 10 and 20% of the initial C content of all treatments, except

the solid fraction, where it represented >100%.

Methane emissions varied widely between treatments dur-

ing the experiment (Fig. 3B). Th e lowest CH4 emissions were

observed from the PAM-sup treatment where emission rates

were generally constant and always <0.05 g C ton−1 h−1 (fresh

weight basis). Emissions from the untreated slurry were signifi -

cantly higher (P < 0.05) than from all other treatments, except

between Days 2 and 8, where the solid fraction exhibited the

highest emissions with rates ranging from 0.64 to 9.05 g C

ton−1 h−1. However, CH4 emissions from the solid fraction

occurred only during the fi rst 10 d of the experiment. Earlier

turning (i.e., before Day 13) may have reduced CH4 emissions

by increasing oxygen supply at the time of highest microbial ac-

tivity. Th e liquid and PAM-sed fractions behaved similarly, and

emission rates from both fractions were not signifi cantly diff er-

ent (P > 0.05). For the untreated slurry, the liquid fraction, and

the PAM-sed fraction, CH4 emissions reached a maximum in

the last days of the experiment after 7 wk of storage.

After 48 d of storage, <1 kg C ton−1 was lost as CH4 emis-

sions from all treatments, with the greatest amount lost from

the solid fraction (Table 2). As a percentage of the initial

total C, it appears that 2% was lost via CH4 emission from

the untreated slurry, whereas <1.7% was lost from the other

fractions, with only approximately 0.6% from the solid and

PAM-sup fractions. In terms of soluble C, C lost via CH4

emissions represented up to 46% of the initial soluble C.

Fig. 3. Average emissions rates of CO2 (A), CH

4 (B), NH

3 (C), and N

2O (D) from the untreated slurry, liquid fraction, polyacrylamide-sediment

(PAM-sed) fraction, polyacrilamide-supernatant (PAM-sup) fraction, and solid fraction during storage expressed per ton of effl uent (n = 3). Standard errors removed for clarity. Arrows indicate days when mixing took place in the solid faction treatment (Days 13, 19, and 29) and stirring in all other treatments (Day 29 only).

Fangueiro et al.: Gaseous Emissions from Storage of Treated Cattle Slurry 2327

Nitrogen EmissionsAmmonia emissions followed a similar trend in all treat-

ments except the solid fraction, where signifi cant NH3 emis-

sions were observed only during the fi rst 6 d of the experi-

ment (Figure 3C). Ammonia emissions rates varied between

approximately 10 and 50 mg N ton−1 h−1 (fresh weight basis)

in all treatments during the experiment.

As for the other gases studied, the NH3 emission rates

and the temperature followed the same trend. In the case of

the PAM-sed fraction, a signifi cant correlation (r2 = 0.42;

P < 0.05) was determined between the NH3 emission rates

and the temperature of the material, but in all other fractions

the trend was not signifi cant (r2 < 0.20; P > 0.05).

Th e greatest quantity of N lost by NH3 emissions during the

48 d of storage was measured from the liquid fraction with a value

of 32.2 g N ton−1, followed by the PAM-sup and PAM-sed frac-

tions with 28.1 and 25.8 g N ton−1, respectively. Th e untreated

slurry and solid fraction resulted in lower N losses via NH3 emis-

sions with only 20.2 and 3.8 g N ton−1, respectively. In all treat-

ments, N losses via NH3 emissions represented <2% of total initial

N and <4% of total initial NH4+. For the solid fraction, <0.1% of

total initial N and <0.5% of total initial NH4+ was lost as NH

3.

Nitrous oxide emissions rates from the solid fraction were

always >3.0 mg N ton−1 h−1 (fresh weight basis) and peaked

on two occasions, on Day 6 (86.2 mg N ton−1 h−1) and on

Day 24 (55.0 mg N ton−1 h−1) (Fig. 3D). From all the other

fractions, N2O emissions were not statistically diff erent from

each other during the experiment (P > 0.05), with values al-

ways <0.7 mg N ton−1 h−1. After Day 39, N2O emissions were

much reduced from all fractions, including the solid fraction.

As previously stated for NH3, there was a trend between

N2O emission rate and temperature of the material. How-

ever, a signifi cant correlation between the temperature and

the N2O emission rates was only observed with the untreated

slurry (r2 = 0.41; P < 0.05) and with the solid fraction

(r2 = 0.56; P < 0.05).

Th e quantity of total N2O lost after 48 d of storage was not

statistically diff erent (P > 0.05) between treatments, except for

the solid fraction, where the greatest quantity of N2O was emit-

ted (29.2 g N ton−1) (Table 2). Th e total amount of N2O lost

during the 48 d of storage represented <1.0% of total N in all

treatments. Th is quantity is relatively high given that the IPCC

default emission factor is 0.02% of the initial N; however, Di-

nuccio et al. (2008) also reported N2O emissions equivalent to

4.71% of total N during storage of pig slurry.

Greenhouse Gas EmissionsTh e net total GHG emissions were calculated as CO

2

equivalents from the emissions of CH4 and N

2O. Ammonia

was not considered because its contribution to total GHG

emissions is negligible (Berg et al., 2006). Th e highest GHG

emissions (Table 2) were found from the solid fraction and

the untreated slurry. Indeed, a good correlation (r2 = 0.95;

P < 0.05) between the dry matter content of the fractions

and the total GHG emissions was observed at the end of the

experiment. Less than 1 kg CO2 equivalents ton−1 of GHG

was lost from the PAM-sup fraction during storage, refl ecting

the low emissions of N2O and CH

4 observed during storage

of this fraction. Methane contributed to >90% of the GHG

for all slurry fractions, except for the solid fraction, where it

represented only 67% of the GHG.

Eff ect of Slurry Separation on Gas Emissions

during StorageIn the previous sections, we compared gaseous emissions

that occurred during storage of untreated slurry and the separate

Table 2. Cumulative emissions of carbon dioxide, methane, nitrous oxide, and ammonia from diff erent effl uents during a 48 d storage period expressed by tonne of fresh material. Mean and SEM are given (n = 3).

Untreated slurry Solid fraction Liquid fraction PAM-sed† PAM-sup

CO2

kg C ton−1 0.65 ± 0.01b‡ 25.02 ± 0.08a 0.55 ± 0.02b 0.54 ± 0.01b 0.28 ± 0.02c

% of initial total C 2.35 ± 0.05d 17.99 ± 0.06a 2.89 ± 0.10c 2.74 ± 0.07cd 5.51 ± 0.34b

% of initial soluble C 15.68 ± 0.33bc >100a 15.78 ± 0.54bc 19.13 ± 0.46b 11.83 ± 0.74c

CH4

kg C ton−1 0.55 ± 0.01b 0.76 ± 0.01a 0.29 ± 0.01d 0.33 ± 0.01c 0.03 ± 0.00e

% of initial total C 2.01 ± 0.02a 0.55 ± 0.01d 1.50 ± 0.01c 1.70 ± 0.02b 0.59 ± 0.01d

% of initial soluble C 13.40 ± 0.14b 46.45 ± 0.77a 8.19 ± 0.07d 11.85 ± 0.15c 1.27 ± 0.03e

N2O

g N ton−1 0.38 ± 0.04b 29.19 ± 0.35a 0.36 ± 0.02b 0.35 ± 0.02b 0.13 ± 0.01b

% of initial total N 0.02 ± 0.01b 0.62 ± 0.01a 0.01 ± 0.01b 0.01 ± 0.01b 0.01 ± 0.01b

% of initial NH4

+ 0.03 ± 0.01b 3.22 ± 0.04a 0.03 ± 0.01b 0.03 ± 0.01b 0.01 ± 0.01b

NH3

g N ton−1 20.18 ± 0.34d 3.80 ± 0.62e 32.21 ± 0.77a 25.82 ± 0.86c 28.09 ± 0.79b

% of initial total N 0.78 ± 0.01d 0.08 ± 0.01e 1.29 ± 0.03b 0.97 ± 0.04c 2.00 ± 0.04a

% of initial NH4

+ 1.53 ± 0.02d 0.42 ± 0.07e 2.61 ± 0.06b 2.19 ± 0.07c 3.06 ± 0.09a

Total GHG

kg CO2 eq ton−1 12.89 ± 0.14 26.10 ± 0.40 6.70 ± 0.06 7.78 ± 0.10 0.73 ± 0.02

% N2O 0.87 33.11 1.60 1.32 5.25

%CH4

99.13 66.89 98.40 98.68 94.75

† PAM-sed, polyacrylamide-sediment fraction; PAM-sup, polyacrylamide-supernatant fraction.

‡ Values followed by the same letter are not signifi cantly diff erent (P < 0.05) by LSD test.

2328 Journal of Environmental Quality • Volume 37 • November–December 2008

fractions obtained by slurry separation. To estimate the eff ect of

slurry separation on total gaseous emissions during storage, the

gaseous emissions balance of the slurry separation processes must

be considered using the relative proportion of each fraction after

separation (see Materials and Methods). Neither screw-press slur-

ry separation nor chemically enhanced separation results in equal

proportions of solid and liquid fractions. Th e relative amounts of

each fraction obtained after mechanical, chemical, and combined

(mechanical followed by chemical) separation of slurry are shown

in Table 3. Th ese values were based on the relative proportions of

the diff erent fractions using results of the separations performed

during the experiment presented here and on results obtained in

previous work (Fangueiro et al., 2008a; Fangueiro et al., 2008b).

Mechanical separation (estimated sum of the solid and liquid

fractions) led to an increase of 38% of the NH3 emissions relative

to untreated slurry, whereas the combined separation techniques

led to an increase of only 15% (Table 4). Th is is mainly due to

the high emissions observed from the solid fraction, whereas

chemically enhanced separation of the liquid fraction led to a

decrease of NH3 emissions. Both separation processes tended to

decrease CH4 emissions during storage (>25% with single separa-

tion and up to 45% by combining both treatment processes).

Slurry separation led to a marked increase of CO2 and N

2O

emissions when the mechanical or combined process were used,

but, as in the case of the CH4, the treatment by chemically

enhanced settling caused a decrease of approximately 25% of

emissions relative to the liquid fraction. For CO2 and N

2O, the

overall increase compared with untreated slurry was mainly due

to the high emissions observed from the solid fraction. In terms

of total GHGs (CO2, CH

4, and N

2O emissions expressed as

CO2 equivalents), it appeared that both separation processes led

to a decrease of the GHG emissions during storage (Table 4).

Discussion

Carbon EmissionsResults obtained in this study showed that CO

2 emissions

during storage of untreated slurry and slurry fractions were

directly related to the total C content of each effl uent. Th e

highest CO2 emissions were observed from the solid fraction

and the lowest from the PAM-sup fraction, which have the

higher and lower C content, respectively. Pattey et al. (2005)

also observed higher CO2 emissions from composting dairy

cattle manure than from the untreated slurry but only during

the fi rst days of storage, and diff erences between both treat-

ments in terms of CO2 emissions were not as signifi cant as in

our study. Such diff erences may exist because the solid fraction

is probably mostly anaerobic with some aerobic areas, whereas

all other fractions and untreated slurry may be considered fully

anaerobic. Indeed, oxygen promotes the aerobic degradation of

organic components. Th is microbial activity induces an increase

in the temperature of organic material (as observed in the pres-

ent study with the solid fraction), which stimulates a greater

microbial transformation of organic matter.

Higher percentages of total C lost as CO2 were observed in

the PAM-sup than in the untreated slurry, the liquid fraction,

or the PAM-sed fraction. Th is was probably due to the greater

quantity of readily biologically available C in the PAM-sup

fraction, due to smaller particle size and a higher percentage

of volatile solids.

Th e decrease of CO2 emission rates after Day 6 in all treat-

ments may have been the result of decreasing organic material

consumed by microbes, but, in the case of the solid fraction, it

could also be related to a decrease of O2 levels. Indeed, barrels

containing the solid fraction were turned on Days 13 and 19,

and, immediately after turning, CO2 emission rates increased

probably due to the increase of O2 levels deep inside the heap.

In all other treatments, CO2 emission rates started to increase

after Day 10, but in these cases CO2 emissions were probably

infl uenced by temperature. Th e correlation between CO2 emis-

sion rates and the temperature observed in all treatments is well

documented and has been reported by Pattey et al. (2005).

Th e present work showed that during storage of the un-

treated slurry and slurry fractions, the amount of total C

lost via CO2 emissions was higher than via CH

4 emissions.

Similarly, Moller et al. (2004) reported that during storage of

pig and cattle manure, CO2 emissions were the predominant

Table 3. Relative amount of each fraction obtained after separation of slurry (screw press only and screw press + sediment settling with polyacrylamide [PAM]) and separation of liquid fraction (sediment settling with PAM).

Screw press only

Sediment settling with PAM

Screw press + sediment settling

with PAM

––––––––––––––––––––%––––––––––––––––––––Untreated slurry 100 100

Solid fraction 15 15

Liquid fraction 85 100

PAM-sed fraction 60 51

PAM-sup fraction 40 34

Table 4. Eff ect of diff erent processes of slurry separation on the balance of gaseous losses during storage compared with the untreated effl uent (untreated slurry or liquid fraction), taking into account the relative amount of each separated fraction. Percentage of emissions observed in the untreated effl uent.

Untreated slurry Screw press only Liquid fractionSediment settling

with PAM† Untreated slurryScrew press + sediment

settling with PAM

––––––––––––––––––––––––––––––––––––––––––––––––––%––––––––––––––––––––––––––––––––––––––––––––––––––CO

2100 650 100 79 100 634

N2O 100 1239 100 72 100 1216

NH3

100 138 100 83 100 115

CH4

100 64 100 74 100 53

GHG‡ 100 74 100 74 100 62

† PAM, polyacrylamide.

‡ GHG, the sum of the CO2 equivalents for CH

4 and N

2O emissions.

Fangueiro et al.: Gaseous Emissions from Storage of Treated Cattle Slurry 2329

form of C gaseous losses. However, C emissions during and

after soil application may also diff er signifi cantly between

slurry fractions. Hence, emissions at the spreading/application

stage have to be assessed and considered to estimate the over-

all eff ect of the combined slurry separation on C emissions.

Th e proportion of total C lost via CO2 and CH

4 varied

widely between treatments. In the solid fraction, the total C

lost via CH4 emissions represented only 3% of the total C lost

via CO2, whereas in all other treatments this percentage was

>50%, except in the PAM-sup fraction, where it was 10%.

Pattey et al. (2005) showed that CH4 emissions from com-

posting manure were positively correlated with the inorganic

N and inorganic C content. Th ese authors considered that

ammonium stimulates CH4 production because methanogen-

ic bacteria used NH3 as source of N. In the present study, the

PAM-sup fraction with a low C/N ratio and one of the lowest

initial NH4–N content induced very low CH

4 emissions dur-

ing the 48 d of storage, whereas the untreated slurry with a

high C/N ratio and the highest initial NH4–N content led to

the highest emission rates, agreeing with conclusions reported

by Pattey et al. (2005). Th e high CH4 emission rates observed

during the fi rst days in the solid fraction treatment could have

been due to the limited oxygen supply and to the high C/N

ratio of this fraction, but because its NH4–N content was

relatively low, these emissions ended after 10 d. Furthermore,

after 13 d of storage, the availability of easily degradable C in

this fraction was reduced due to the high emissions of CO2

and CH4. Chadwick (2005) measured CH

4 losses from cattle

manure heaps and reported cumulative losses of between 1.8

and 4.4% of total C in the initial heaps, with the majority of

the emission occurring within the fi rst month of heap estab-

lishment with no active turning of the heaps.

Many authors (Külling et al., 2002; Moller et al., 2004;

Hindrichsen et al., 2006) have reported a slow increase of the

slurry CH4 emissions up to a peak during the fi rst weeks of

storage, followed by a decrease. Th e increase in CH4 emissions

observed in the untreated slurry, liquid, and PAM-sed treat-

ment at the end of the experiment could correspond to this

peak. Th e timing of the CH4 emission peak varied widely be-

tween treatments and could have been missed even after more

than 48 d of storage, suggesting that CH4 emission measure-

ments should be continued for a long time period (Hindrich-

sen et al., 2006). As in the case of CO2, the general trend

of CH4 emissions in all treatments except the solid fraction

followed the temperature trend. Many authors (Massé et al.,

2003; Moller et al., 2004; Pattey et al., 2005) also observed a

positive correlation between CH4 emissions and the tempera-

ture of manure or slurry.

Nitrogen EmissionsResults obtained in the present work showed that NH

3

emissions during storage were strongly infl uenced by the dry

matter and by the NH4+–N content of the effl uent as reported

in previous studies (Amon et al., 2001; Chadwick, 2005; Amon

et al., 2006). Indeed, NH3 emissions from all effl uents except

the solid fraction were similar during the fi rst 13 d of stor-

age, but after this period the NH3 emissions from the liquid,

PAM-sed, and PAM-sup fractions were higher relative to the

untreated slurry, with the highest amount of NH3 lost observed

in the liquid fraction. Ammonia emissions from the solid frac-

tion treatment lasted for a short period of time (6 d) compared

with the results obtained by Chadwick (2005), who observed

NH3 emissions from cattle manure heaps during a 3-wk period.

Such diff erences may be due to N-immobilization because the

solid fraction had a high C/N ratio. Furthermore, water vapor

released from the warm solid fraction occasionally caused con-

densation in the outlet tubing, which may have absorbed some

of the NH3 emitted from this slurry fraction. It is also possible

that some NH3 losses could have occurred during mixing of the

solid fraction, but this was not measured because the barrel lids

were removed for a few minutes after mixing. Th e cumulative

NH3 emissions from the solid treatment observed here are in

the same range as those reported by Hansen et al. (2006) from

a study of GHG and NH3 emissions during storage of the solid

fraction produced by mechanical separation of pig slurry.

As in our study, Amon et al. (2006) reported higher NH3

emissions during storage of the separated liquid than from

the untreated slurry and showed that NH3 emissions from

untreated slurry storage represent only a small percentage of

the emissions observed after application to soil, whereas the

opposite situation was observed with the liquid fraction. It is

important to minimize NH3 emissions during storage because

NH3 has an adverse eff ect on the environment (Ferm, 1998).

Furthermore, the slurry fractions are subsequently used as

organic fertilizers, so it is important to reduce N losses during

storage. A solution to reduce such emissions could be to cover

the slurry storage pit or to compact and cover the manure

heap with plastic (Chadwick, 2005). However, results ob-

tained in this study also showed that NH3 emissions and tem-

perature are positively correlated, so keeping the stored slurry

and farmyard manure cool could reduce NH3 emissions. At

the farm-scale, a thick surface crust is generally formed during

slurry storage, which can reduce NH3 emissions compared

with non-crusted stores by approximately 50% (Misselbrook

et al., 2005). Misselbrook et al. (2005) showed that the crust

formation is related to the slurry dry matter content (no crust

formation in slurries with <1% dry matter) and by the nature

of the dry matter. Th erefore, we would expect to observe thin-

ner crusts with our stored liquid fractions (liquid, PAM-sed,

and PAM-sup) and consequently higher NH3 emissions.

Signifi cantly (P < 0.05) higher N2O emissions were ob-

served from the solid fraction treatment than from all other

treatments, including the untreated slurry. Pattey et al. (2005)

also reported higher N2O emissions from composted and

stockpiled manure than from slurry. Similarly, Külling et al.

(2003) found low total N2O losses with slurry (<0.1% of

initial total N after 5 wk of storage) and with liquid manure

(<2%) but higher N2O losses with farmyard manure (up to

46%). Th e low N2O emissions observed in our untreated slur-

ry and liquid fractions would have been due to their anaerobic

conditions that result in little or no nitrifi cation of NH4+ to

NO3−, and consequently no or low N

2O emissions.

2330 Journal of Environmental Quality • Volume 37 • November–December 2008

Th e N2O emissions observed in the fi rst 10 d in all treat-

ments were probably due to nitrifi cation and not denitrifi ca-

tion because the NO3− content of the treatments at the begin-

ning of the experiment was negligible. In the case of the solid

fraction where the highest N2O emissions were observed, this

hypothesis that the fi rst emission peak was mainly due to ni-

trifi cation is in agreement with the end of the NH3 emissions

after Day 7 because part of the NH4+ could have been trans-

formed to NO3 or immobilized. Paillat et al. (2005) measured

the N2O emissions from heaps of manure composting and

attributed the N2O emissions observed in the fi rst days to

nitrifi cation and probable simultaneous denitrifi cation near

the surface of the heap where aerobic conditions and lower

temperatures can be found.

Th e overall eff ect of the combined slurry separation on N

emissions may be estimated only after consideration of the N

emissions that occurred at the soil application stage.

Greenhouse Gas Emissions and Eff ect of Slurry SeparationGreater GHG emissions (total CO

2, CH

4, and N

2O emis-

sions expressed as CO2 equivalents) were observed during

storage of effl uents with higher DM contents, in agreement

with results reported by Külling et al. (2003), who showed

that the GHG potential is generally higher with the farmyard

manure system than with liquid manure. Less than 1 kg CO2

eq ton−1 of GHG was lost from the PAM-sup fraction during

storage, which refl ects the low emissions of N2O and CH

4

observed during storage of this fraction. Th is aspect is particu-

larly relevant if we consider that this PAM-sup fraction may

be used for fertigation. Th is implies that it is safe to store large

quantities of this fraction in lagoons for periods longer than 3

mo with little eff ect on the atmosphere. Th e solid fraction can

be applied to land just after separation or composted. Con-

sidering the high GHG emissions observed during the 48 d

of storage, it appears that immediate application to land after

separation would reduce losses from storage; however, losses

during and after soil application may be enhanced. Hence,

GHG emissions at the application stage have to be assessed

and considered to draw overall conclusions on the eff ect of

the combined slurry separation.

Greenhouse gas emissions observed in the present study

mainly originated from CH4 emissions. Similarly, Berg et al.

(2006) and Amon et al. (2006) showed that CH4 is the pre-

dominant GHG emitted from slurry stores, and they conclud-

ed that an effi cient reduction of CH4 emissions during storage

is the best strategy to reduce GHG emissions at this stage.

Both of the separation processes we used tended to de-

crease CH4 emissions during storage (>35% with a single

separation and up to 50% by combining both processes).

However, the slurry separation by screw press induced an

increase of NH3 emissions during storage, but the liquid frac-

tion separation by chemically enhanced settling led to a small

decrease of these NH3 emissions. Th e same situation was ob-

served in the case of the CO2 and N

2O because the increased

N2O and CO

2 emissions were mainly due to the high emis-

sions observed from the solid fraction. Overall, the combined

slurry separation process proposed in our work reduced the

total GHG emissions during storage of the separated fractions

relative to the untreated slurry.

ConclusionsImportant emissions of GHG, CO

2, and NH

3 occurred

during storage of cattle slurry. Slurry treatment by mechani-

cally and chemically enhanced settling separation is useful

to reduce slurry dry matter content but has the potential to

reduce gaseous emissions. In the present study, we compared

the gaseous emissions observed during winter storage of

separated slurry fractions and untreated slurry to assess the

effi ciency of such treatments in reducing emissions. Relative

to the untreated slurry, the solid fraction obtained after screw

press separation emitted signifi cantly higher amounts of CO2

and N2O, whereas all other slurry fractions studied emitted

lower or similar amounts. In the case of CH4, emissions from

slurry fractions were always lower from the untreated slurry,

except in the solid fraction, where emissions were much

greater but restricted to the fi rst 6 d of storage. Emissions of

NH3 were strongly infl uenced by the dry matter content of

the fraction, and higher emissions were observed from the

liquid fractions.

Slurry treatments by screw press separation, PAM sedi-

mentation, or the combined separation process proposed here

(screw press + PAM treatment) led to a decrease of GHG

emissions during storage of separated fractions relative to the

untreated slurry. Th e combined scheme enhanced this reduc-

tion of GHG emissions relative to the mechanical process

(screw press only). Furthermore, in the case of CO2, N

2O,

and NH3, where the single screw press process induced an

increase of gas emissions relative to the untreated slurry, use

of the combined separation process mitigated this increase.

Th erefore, the combined slurry separation process (screw press

+ PAM treatment) can be considered a good tool for slurry

management. Because the current study was performed under

winter storage conditions, the results should not be extrapo-

lated to emissions under summer conditions or emissions

from a whole year.

Th e present study considered emissions only from the

storage stage of untreated and treated slurry, and any nutri-

ents and GHGs saved during storage may be lost after land

spreading if suitable application or incorporation methods are

not used to minimize such losses. Th erefore, more studies in-

cluding manure and slurry storage and application to land are

needed to determine the overall impact of slurry separation on

GHG and NH3 emissions.

AcknowledgmentsTh is work was funded by the Green Dairy Project–Interreg

III B Atlantic Area, no. 100. Th e authors thank the two

reviewers for their useful comments and constructive

suggestions for this paper.

Fangueiro et al.: Gaseous Emissions from Storage of Treated Cattle Slurry 2331

ReferencesAmon, B., T. Amon, J. Boxberger, and C. Alt. 2001. Emissions of NH

3,

N2O, and CH

4 from dairy cows housed in a farmyard manure tying

stall (housing, manure storage, manure spreading). Nutr. Cycling Agroecosyst. 60:103–113.

Amon, B., V. Kryvoruchko, T. Amon, and S. Zechmeister-Boltenstern. 2006. Methane, nitrous oxide, and ammonia emissions during storage and after application of dairy cattle slurry and infl uence of slurry treatment. Agric. Ecosyst. Environ. 112:153–162.

Berg, W., R. Brunsch, and I. Pazsiczki. 2006. Greenhouse gas emissions from covered slurry compared with uncovered during storage. Agric. Ecosyst. Environ. 112:129–134.

Chadwick, D.R. 2005. Emissions of ammonia, nitrous oxide, and methane from cattle manure heaps: Eff ect of compaction and covering. Atmos. Environ. 39:787–799.

Chadwick, D.R., B.F. Pain, and S.K.E. Brookman. 2000. Nitrous oxide and methane emissions following application of animal manures to grassland. J. Environ. Qual. 29:277–287.

Dinuccio, E., W. Berg, and P. Balsari. 2008. Gaseous emissions from the storage of untreated slurries and the fractions obtained after mechanical separation. Atmos. Environ. 42:2448–2459.

Fangueiro, D., J. Pereira, D. Chadwick, J. Coutinho, N. Moreira, and H. Trindade. 2008a. Laboratory assessment of the eff ect of cattle slurry pre-treatment on organic N degradation after soil application and N

2O

and N2 emissions. Nutr. Cycling Agroecosyst. 80:107–120.

Fangueiro, D., M. Senbayran, H. Trindade, and D. Chadwick. 2008b. Cattle slurry treatment by screw press separation and chemically enhanced settling: Eff ect on greenhouse gas emissions after land spreading and grass yield. Bioresour. Technol. 99:7132–7142.

Fangueiro, D., J. Pereira, J. Coutinho, N. Moreira, and H. Trindade. 2008c. NPK farm-gate nutrient balances in dairy farms from Northwest Portugal. Eur. J. Agron. 28:625–634.

Ferm, M. 1998. Atmospheric ammonia and ammonium transport in Europe and critical loads: A review. Nutr. Cycling Agroecosyst. 51:5–17.

Flessa, H., and F. Beese. 2000. Laboratory estimates of trace gas emissions following surface application and injection of cattle slurry. J. Environ. Qual. 29:262–268.

Genermont, S., P. Cellier, D. Flura, T. Morvan, and P. Laville. 1998. Measuring ammonia fl uxes after slurry spreading under actual fi eld conditions. Atmos. Environ. 32:279–284.

van Groenigen, J.W., G.J. Kasper, G.L. Velthof, A. van den Pol-van Dasselaar, and P.J. Kuikman. 2004. Nitrous oxide emissions from silage maize fi elds under diff erent mineral nitrogen fertilizer and slurry applications. Plant Soil 263:101–111.

Hansen, M.N., K. Henriksen, and S.G. Sommer. 2006. Observations of production and emission of greenhouse gases and ammonia during storage of solids separated from pig slurry: Eff ects of covering. Atmos. Environ. 40:4172–4181.

Hindrichsen, I.K., H.R. Wettstein, A. Machmüller, B. Jörg, and M. Kreuzer. 2006. Methane emission, nutrient degradation, and nitrogen turnover in dairy cows and their slurry at diff erent milk production scenarios with and without concentrate supplementation. Agric. Ecosyst. Environ. 113:150–161.

Houba, V.J.G., I. Novozamsky, and E. Tenminghoff . 1994. Soil analysis procedures. Dep. of Soil Science and Plant Nutrition, Wageningen Agricultural Univ., Th e Netherlands.

IPCC. 1996. Climate change 1995. p. 572. In J.T. Houghton et al. (ed.) Th e science of climate change. Cambridge Univ. Press, Cambridge, UK.

IPCC. 2001. Good practise guidance and uncertainty management in national greenhouse gas inventories. In J. Penman et al. (ed.) IPCC national greenhouse gas inventories programme, Technical support unit, Hayama, Japan.

IPCC/OECD/IEA. 1997. Revised 1996 IPCC guidelines for national greenhouse gas inventories, Vol. 3. UK Meteorological Offi ce, Bracknell, UK.

Külling, D.R., F. Dohme, H. Menzi, F. Sutter, P. Lischer, and M. Kreuzer. 2002. Methane emissions of diff erently fed dairy cows and corresponding methane and nitrogen emissions from their manure during storage. Environ. Monit. Assess. 79:129–150.

Külling, D.R., H. Menzi, F. Sutter, P. Lischer, and M. Kreuzer. 2003. Ammonia, nitrous oxide, and methane emissions from diff erently stored dairy manure derived from grass- and hay-based rations. Nutr. Cycling Agroecosyst. 65:13–22.

Massé, D.I., F. Croteau, N.K. Patni, and L. Masse. 2003. Methane emissions from dairy cow and swine manure slurries stored at 10°C and 15°C. Can. Biosyst. Eng. 45:6.1–6.6.

Mattila, P.K. 1998. Ammonia volatilization from cattle slurry applied to grassland as aff ected by slurry treatment and application technique-fi rst year results. Nutr. Cycling Agroecosyst. 51:47–50.

Misselbrook, T.H., S.K.E. Brookman, K.A. Smith, T. Cumby, A.G. Williams, and D.F. McCrory. 2005. Crusting of stored dairy cattle slurry to abate ammonia emissions: Pilot-scale studies. J. Environ. Qual. 34:411–419.

Moller, H.B., S.G. Sommer, and B.K. Ahring. 2002. Separation effi ciency and particle size distribution in relation to manure type and storage conditions. Bioresour. Technol. 85:189–196.

Moller, H.B., S.G. Sommer, and B.K. Ahring. 2004. Biological degradation and greenhouse gas emissions during pre-storage of liquid animal manure. J. Environ. Qual. 33:27–36.

Paillat, J.M., P. Robin, M. Hassouna, and P. Leterme. 2005. Predicting ammonia and carbon dioxide emissions from carbon and nitrogen biodegradability during animal waste composting. Atmos. Environ. 39:6833–6842.

Pattey, E., M.K. Trzcinski, and R.L. Desjardins. 2005. Quantifying the reduction of greenhouse gas emissions as a result of composting dairy and beef cattle manure. Nutr. Cycling Agroecosyst. 72:173–187.

Peräla, P., P. Kapainen, M. Esala, S. Tíñela, and K. Regina. 2006. Infl uence of slurry and mineral fertiliser application techniques on N

2O and CH

4

fl uxes from a barley fi eld in southern Finland. Agric. Ecosyst. Environ. 117:71–78.

Pereira, J.L., D. Fangueiro, J. Coutinho, N. Moreira, and H. Trindade. 2005. Separação de sólidos e nutrientes com PAM e bentonite em chorumes bovinos. p. 497–501. In Proc. XV Congress of Animal Science- ZOOTEC I&D UTAD, Vila Real, Portugal.

Rhode, L., M. Pell, and S. Yamulki. 2006. Nitrous oxide, methane, and ammonia emissions following slurry spreading on grassland. Soil Use Manage. 22:229–237.

Rochette, P., D.A. Angers, M.H. Chantigny, N. Bertrand, and D. Côté. 2004. Carbon dioxide and nitrous oxide emissions following fall and spring applications of pig slurry to an agricultural soil. Soil Sci. Soc. Am. J. 68:1410–1420.

Sommer, S.G., and N.J. Hutchings. 2001. Ammonia emission from fi eld applied manure and its reduction–invited paper. Eur. J. Agron. 15:1–15.

Statistix. 2000. Statistix 7.0 user’s guide. Statistix, Tallahassee, FL.

Vanotti, M.B., and P.G. Hunt. 1999. Solids and nutrient removal from fl ushed swine manure using polyacrylamides. Trans. ASAE 42:1833–1840.

Vanotti, M.B., D.M. Rashash, and P.G. Hunt. 2002. Solid-liquid separation of fl ushed swine manure with PAM: Eff ect of wastewater strength. Trans. ASAE 45:1959–1969.

Wulf, S., M. Maeting, and J. Clemens. 2002a. Eff ect of application technique on the emission of trace gases (NH

3, CH

4, N

2O) after spreading

co-fermented slurry on arable and grassland; Part I: Ammonia volatilization. J. Environ. Qual. 31:1789–1794.

Wulf, S., M. Maeting, and J. Clemens. 2002b. Application technique and slurry co-fermentation eff ects on ammonia, nitrous oxide and methane emissions after spreading: II. Greenhouse gas emissions. J. Environ. Qual. 31:1795–1801.

Yamulki, S., and S.C. Jarvis. 1999. Automated chamber technique for gaseous fl ux measurements: Evaluation of a photo-acoustic infrared spectrometer-trace gas analyser. J. Geophys. Res. 104:5463–5469.