Agriculture, Ecosystems and Environment 146 (2012) 23 33

Contents lists available at SciVerse ScienceDirect

Agriculture, Ecosystems and Environment

jo ur n al homepage: www.elsev ier .co

The po roumateri se

D.S. Pow . MK.W.T. Ga Rothamsted Rb ADAS Gleadth

a r t i c l

Article history:Received 4 JulReceived in reAccepted 7 OcAvailable onlin

Keywords:Soil organic caSoil organic matterLong-term experimentsSoil carbon stocksReduced tillageOrganic amendmentsBiosolidsClimate chang

o qua1) a ng fanual mulationaon of

by on average 60 20 (farm manures), 180 24 (digested biosolids), 50 15 (cereal straw), 60 10 (greencompost) and an estimated 60 (paper crumble). SOC accumulation declines in long-term experiments(>50 yr) with farm manure applications as a new equilibrium is approached. Biosolids are typically alreadyapplied to soil, so increases in SOC cannot be regarded as mitigation. Large increases in SOC were deducedfor paper crumble (>6 t C ha1 yr1) but outweighed by N2O emissions deriving from additional fertiliser.

1. Introdu

There arand citizensthe quantit

1. Because opropertieand the rtheir biovices, as(http://wThis roletem Asseand in don Globa2011b).

2. Because get, (150

CorresponE-mail add

0167-8809/$ doi:10.1016/j.e mitigationCompost offers genuine potential for mitigation because application replaces disposal to landll; it alsodecreases N2O emission.

2011 Elsevier B.V. All rights reserved.

ction

e two sets of reasons why governments, land managers should be concerned about maintaining or increasingy of organic carbon (C) in agricultural soils.

rganic C content has a profound inuence on many soils and functions that affect both agricultural productionoles that soils play in the wider environment throughphysical and economic impacts on ecosystem ser-

recognised in the Millennium Ecosystem Assessmentww.millenniumassessment.org/en/Framework.aspx).

of soil C is also emphasised in the UK National Ecosys-ssment (UK National Ecosystem Assessment, 2011)iscussion of soil functions in the UK Foresight studyl Food and Farming (Foresight, 2011; Powlson et al.,

soils are a signicant stock of C within the global C bud-0 Pg C in soils compared to 760 Pg C in the atmosphere,

ding author. Tel.: +44 1582 763133.ress: andy.whitmore@rothamsted.ac.uk (A.P. Whitmore).

(e.g. Powlson et al., 2011c), changes in the soil C stock have impli-cations for the mitigation or worsening of climate change (e.g.Smith et al., 2008).

The EU Commission has identied organic carbon (or organicmatter) decline as one of the main threats to soils within Europe(Jones et al., 2004). In general, a soil with higher organic carboncontent will have more stable structure than the same soil at lowerorganic carbon content, be less prone to runoff, erosion or surfacecapping and have a greater water inltration rate, water reten-tion and greater porosity (Snyder and Vazquez, 2005; Abiven et al.,2009; Bhogal et al., 2009; Johnston et al., 2009). It has been shown,at least in some situations, that even small increases in soil organiccarbon (SOC) can markedly inuence aggregate stability, waterinltration and the energy required for tillage (Blair et al., 2006;Watts et al., 2006).

Regarding the role of soils within the global carbon cycle, therehas been much discussion of the possibility of mitigating climatechange through C sequestration by increasing SOC stocks (e.g.Smith et al., 2008). Although the largest stocks of SOC on an areabasis are often in non-agricultural situations (e.g. forests, wetlands),agricultural soils are amenable to alteration through managementinterventions. Also, in many regions of the world including Europe,

see front matter 2011 Elsevier B.V. All rights reserved.agee.2011.10.004tential to increase soil carbon stocks thal additions in England and Wales: A ca

lsona, A. Bhogalb, B.J. Chambersb, K. Colemana, A.Jouldinga, A.P. Whitmorea,

esearch, Harpenden, Hertfordshire, AL5 2JQ, UKorpe, Meden Vale, Manseld, Nottingham, NG20 9PD, UK

e i n f o

y 2011vised form 5 October 2011tober 2011e 22 November 2011

rbon

a b s t r a c t

Results from the UK were reviewed tcarbon (SOC) stocks as a result of (addition of organic materials includiand paper crumble. The average anC 180 kg C ha1 yr1. Even this accuEurope because farmers practice rotacounteracting increases in SOC. Additim/lo cate /agee

gh reduced tillage or organicstudy

acdonalda,

ntify the impact on climate change mitigation of soil organicchange from conventional to less intensive tillage and (2)rm manures, digested biosolids, cereal straw, green manureincrease in SOC deriving from reduced tillage was 310 kgtion of C is unlikely to be achieved in the UK and northwestl tillage. N2O emissions may increase under reduced tillage,biosolids increased SOC (in kg C ha1 yr1 t1 dry solids added)

24 D.S. Powlson et al. / Agriculture, Ecosystems and Environment 146 (2012) 23 33

agricultural soils cover very large areas so relatively small changesin C stock per unit area may translate into signicant stock changesat the national or regional scale (Smith et al., 2000, 2008).

A net transfer of C from atmospheric CO2 to land (either into soilor vegetatioof climate such as affotural land. (1) applicathave been rburning or disposal todecompositdoes have wgation (Roy(Chung et adecades or librium valumanagemereversible, tSOC must bstood leadinachievable;itive side, tdoes not rerange of othabove. In thor no regragement ca2008; Sey eis increasedincreased e(GWP) 298 2007)).

This pasioned by on the extbe increasefull report uk/Docume

Two typchange fromincreased atities of nein additionreview specthe manageand amounwill be mortemperate rically.

2. Reduced

2.1. Denit

Becausetems variesused in the

Most coWales by mcally 20-25 powered titional tillagwinter-sow

to describe non-plough based cultivation practices. Conservationtillage, another term used in this context, has been dened as atillage system that leaves at least 30% of the soil surface coveredby crop residues (Alvarez, 2005). At the extreme, zero tillage or

, is wt drild tillhallor evmbiny oth

pracctionploug

paphingtermfacerop red; ifllage

prachoppgy.ent sof pntioe. he/broage the Ustrams apearcrop eadslingat isat seing g

neri carb

re ar leadc C daggred in

optively,

reasral cAngeLuo esoil st neing roontraly d2003nt ti0 cm

conevitacorren) is termed C sequestration and represents mitigationchange. It may be achieved through land-use change,restation, or though altered management of agricul-The latter can be accomplished in one of two ways:ion to soil of additional organic C that would otherwiseeturned more rapidly to the atmosphere (e.g. throughdecomposition without incorporation into soil, such as

landll), or (2) use of practices that slow the rate ofion of organic C in soil. However, soil C sequestrationell-known limitations in terms of climate change miti-al Society, 2001). First, the sink capacity for soil C is nitel., 2010), moving towards a maximum after a period ofcenturies as soil C content moves towards a new equi-e characteristic of the soil type and climate for the new

nt practice (Johnston et al., 2009). Second, the process ishus the new management practice leading to increasede continued indenitely. The process is often misunder-g to an over-estimate of the climate change mitigation

see Powlson et al. (2011c) for a discussion. On the pos-he approach is one that can be started immediately,quire development of new technologies and delivers aer benets for soil quality and functioning as mentionedis sense, the approach may be regarded as win-winets. However, changes in SOC content and soil man-n inuence nitrous oxide (N2O) emissions (Rochette,t al., 2008) so that situations could arise where SOC

but the climate change benets are counteracted bymission of N2O which has a global warming potentialtimes that of CO2 on a 100 year timescale (Forster et al.,

per summarises ndings from a review commis-the UK government to critically assess the evidenceent to which SOC stocks in agricultural soils couldd through management changes (DEFRA, 2003). Theof the review is available at: http://randd.defra.gov.nt.aspx?Document=SP0561 6892 FRP.doc.es of management practice were considered: (1) a

conventional tillage to reduced/zero tillage and (2)pplication of organic materials (including greater quan-w materials such as green compost and paper crumble)

to traditional farm manures and crop residues. Theically addressed England and Wales, taking account ofment practices applicable in the region and the typests of organic materials available. However, the resultse widely relevant to north-west Europe and many otheregions; and the reasoning adopted is applicable gener-

tillage

ions and current practice in the UK

the terminology used to describe different tillage sys- in different parts of the world, the systems and terms

UK, and generally in Europe, are outlined here.mmonly, tillage crops are established in England andouldboard ploughing to a depth of at least 20 cm (typi-cm), followed by secondary cultivations (e.g. harrowing,llage, discing/tining) to provide a seedbed (conven-e). Cultivations are carried out in the autumn for alln and some spring-sown crops. Reduced tillage is used

no-till(direcreduceafter sless), o(i.e. coin mantillageconjuntional In this(plougtimes the surtems cremovzero tisystemto be cof ener

Recc.50% (conveods (i.drillingthe tilllar in and Auprobleand aplarger ha1) lof seedarea thsoils thproduc

2.2. Georganic

Thetillageorganiing of proposas oneintuitiseemsa gene2007; 2008;

In greatereectThis cis evenet al., differeleast 3in thewill inand inhere seed is drilled directly into an uncultivated soilling) or simply broadcast onto the soil surface. Whereage is used under UK conditions, seed is usually sownw cultivation (discs or tines) working to 10-15 cm (oren just following rotary-harrowing of the soil surfaceed harrow and drill techniques). In contrast to systemser regions, such as North and South America, reduced

tices in UK and northwest Europe are often carried out in with mouldboard ploughing every 3 to 4 years (rota-hing) to relieve soil compaction and for weed control.er we use the following terms: conventional tillage

to at least 20 cm), zero tillage (no cultivation, some-ed direct drilling) and reduced tillage (cultivation of

soil to a depth of no more than 15 cm). In all tillage sys-esidues such as cereal straw may be either retained or

retained they may either remain on the soil surface (if is performed) or incorporated according to the tillageticed, although large amounts of cereal straw may needed before incorporation incurring a small consumption

urveys in England and Wales (Anon, 2006) show thatrimary tillage practices used mouldboard ploughingnal tillage) and c.43% used reduced tillage meth-avy discs, tines or powered cultivators), with directadcasting (i.e. no cultivation) occurring on only c.7% ofarea. The reason that zero tillage has been less popu-K and northwest Europe, compared to the Americas

lia, has been the build-up of grass weeds, crop diseasend soil compaction, all of which decrease crop yields

to be more prevalent in a moister climate. Also theyields achieved in northwest Europe (often 8-10 t grain

to a larger quantity of straw which can cause problems emergence if left on the surface. The relatively small

under zero tillage in the UK is mainly calcareous claylf-mulch as a result of wet-dry and freeze-thaw cycles,ood tilth in a way not occurring on other soil types.

c issues regarding reduced tillage effects on soilon content

e many claims in the literature that reduced and zero to an increase in SOC, presumably through a slowing ofecomposition due to decreased disturbance and break-egates (e.g. West and Post, 2002). Reduced tillage was

the Stern report on the economics of climate changeon for climate change mitigation (Stern, 2006). Whilst,slower decomposition of SOC under reduced tillageonable, several studies cast serious doubt on this asonclusion (Powlson and Jenkinson, 1981; Baker et al.,rs and Eriksen-Hamel, 2008; Blanco-Canqui and Lal,t al., 2010).under reduced or zero tillage, SOC concentration isar the surface and declines with increasing soil depth,ot distribution and surface deposition of crop residues.sts with soil under conventional tillage where SOCistributed within the cultivated layer (e.g. Machado). Consequently, for comparisons of SOC stock underllage systems, soils must be sampled to a depth of at

(e.g. Poirier et al., 2009), depending on tillage depthventionally cultivated comparison. Shallow samplingbly show greater SOC in the reduced tillage treatmentct sampling invalidates comparisons in many older

D.S. Powlson et al. / Agriculture, Ecosystems and Environment 146 (2012) 23 33 25

studies (as discussed by Baker et al., 2007; Angers and Eriksen-Hamel, 2008; Powlson et al., 2011c). In addition, in a comparisonof SOC in conventionally cultivated and reduced tillage treatmentsin 47 published studies (mainly from North America but includinga few in So(2008) notedepth of tilcommon; thsurface in s(2011) founDespite theHamel (200SOC stock utional plougyears or mo

There ispossible incspatial varithan in ploing it more(Franzluebbthat this vatreatments obtain a w2011) discupling depthacross Canazero-till in sand depth o

A relatebetween soleading to gaccount of an equal mploughed sosites in the21.6 cm. Sesampling obulk densitto express or g C m2)mg C kg1 s(Powlson et

There is lation undetemperate, crop rotatio

A key beservation. Inevaporationthis situatiothus greateAngers andcontributesarid regionsmay well bregions suctillage systein dry regioture for theThere are exrotation of sby continuofacilitates areturns to sfactor in no

Table 1Changes in SOC following zero tillage in the UK.

Site Claycontent (%)

Years SOC change(kg ha1 yr1)a

Reference

amst

worth

dly Ha

icuik I

otts H

dly Ha

icuik I

(se)

data; in zerg a buuding

alysanic

re ispact

clim, as oate

th Am froma froth etder UK sand they are mostly not statistically signicant (e.g. Powlsonkinson, 1981). The results from Headly Hall (I and II) wereoil samples taken from the same experiment; Chaney et al.

sampled one year after Powlson and Jenkinson (1981). Forik (I and II) Ball et al. (1994) sampled 13 years after Powlsonnkinson (1981). The results from Jealotts Hill (Cannell and, 1973; Tomlinson, 1974) should be treated with caution aseriment was sampled only 2 years after the treatments wereshed at a site previously in permanent pasture. Thus SOCt was declining rapidly in both treatments and it is highlynable whether the result can be regarded as representativesituation in long-term arable soils undergoing a change oftreatment.ing an average of the UK studies in Table 1, regardless ofer or not the changes in SOC were statistically signicantcluding the Jealotts Hill result (for the reason explained, the average annual increase in SOC in zero tillage com-to conventional tillage was 310 kg C ha1 yr1 (standard180 kg C ha1 yr1). Because of the wide variation in resultsn sites, this is not signicantly different from zero, though

nsistent with the small trend towards slightly increased SOCnder zero tillage noted by Angers and Eriksen-Hamel (2008)-term comparisons. van Groenigen et al. (2011) reportedn annual increase in SOC in the 030 cm layer equivalentuth America and Europe), Angers and Eriksen-Hameld that an accumulation of SOC at or slightly below thelage in the treatments with full inversion tillage wasis partially offset perceived increases in SOC near theoil under reduced tillage. By contrast, Syswerda et al.d no evidence of this at a single site in North America.

sub-surface accumulation noted by Angers and Eriksen-8) in their review, they did detect a slight trend for totalnder zero tillage to become greater than under conven-hing as the period of the comparisons increased to 15re.

a difculty in sampling to depth in order to detect arease in SOC stock resulting from reduced/zero tillage:ation in SOC is generally greater in deeper soil layersugh-layer soil or its equivalent under zero-till mak-

difcult to detect differences between treatmentsers, 2009). Kravchenko and Robertson (2011) argueriability may be masking differences between tillagein studies where deeper soil is sampled in order tohole prole SOC stock. VandenBygaart et al. (2010,ssed the issue of soil variability in relation to sam-

for tillage comparisons and sampled 11 long-term sitesda. They detected a net increase in SOC stock underome but not all sites, depending on the climatic regionf tillage in the conventional tillage comparison.d sampling issue is the difference in bulk densityils under different tillage treatments - zero-till oftenreater bulk density. Powlson and Jenkinson (1981) tookthis by sampling zero-till soils to a depth containingass of soil to that in a standardised depth of 25 cm inil (a little greater than the usual plough depth): for four

UK the average sampling depth for zero-till soils wase Powlson et al. (2011c) for a recent description of soiln an equivalent mass basis. Such differences in soily between tillage systems draw attention to the needSOC data on a soil mass per area basis (i.e. as t C ha1

rather than as a concentration (i.e. as percentage oroil) as normally expressed from laboratory soil analyses

al., 2011c).some evidence to suggest that increased SOC accumu-r zero tillage may be greater in tropical climates thanthough only if legume cover crops are included in then (Boddey et al., 2009).net of reduced tillage, especially zero-till, is water con-

regions of low or strongly seasonal rainfall and/or high this is often the main driver for adopting the system. Inn, zero tillage often results in increased crop yields andr organic inputs to soil from roots and crop residues.

Eriksen-Hamel (2008) point out that this probably to observations of increased SOC under zero till in semi-

in both North and South America and Australia. Thise relevant in southern Europe, but not in more humidh as northwest Europe where yields under differentms are generally similar. A related benet of zero tillagens is that fallow seasons, needed for conserving mois-

following years crop, can sometimes be eliminated.amples in North America of zero tillage permitting thepring wheat followed by a year of fallow to be replacedus spring wheat (Paustian et al., 1997). Thus, zero tillage

cropping system that leads to increased crop residueoil, and greater SOC accumulation. Again, this is not arthwest Europe.

1. Roth

2. Box

3. Hea

4. Pen

5. Jeal

6. Hea

7. Pen

Meanb

95% CI

n.d.: no a SOC

assuminb Excl

2.3. Ansoil org

Thethe imhumidEuropetal climin Souresults

Datby Smition unof the tillage and Jenfrom s(1985)Penicuand JeFinneythe expestablicontenquestioof the tillage

Takwhethand exabove)pared error: betweeit is costock uin longa meaed 20 5 156 Powlson andJenkinson(1981)

43 6 845 Powlson andJenkinson(1981)

ll I 26 8 292 Powlson andJenkinson(1981)

13 10 234 Powlson andJenkinson(1981)

ill n.d. 2 1365 Cannell andFinney (1973),Tomlinson(1974)

ll II 26 9 607 Chaney et al.(1985)

I 13 23 509 Ball et al.(1994)

310 (180)140 to 760

se: standard error; CI: condence interval.o till treatment minus that in conventional tillage; 030 cm depth,lk density of 1.3 g cm3.

Jealotts Hill.

is of evidence on reduced and zero tillage impacts oncarbon using data from UK

a very limited number of publications giving results onof reduced or zero tillage on soil C under the temperateatic conditions of the UK or nearby regions of northwestpposed to a large body of data from regions of continen-in North America or tropical and sub-tropical regionserica and elsewhere. Table 1 summarises published

seven UK sites.m these experiments, and others in Europe, was used

al. (1998) to estimate potential rates of SOC accumula-zero tillage compared to conventional tillage. Only veites in Table 1 show an increase in SOC due to zero

26 D.S. Powlson et al. / Agriculture, Ecosystems and Environment 146 (2012) 23 33

to >800 kg C ha1 yr1 over 9 years after converting from conven-tional to reduced tillage in an experiment in Ireland. This seemsan unusually large value and is at variance with all other reportedresults.

2.4. Inuenemissions fr

There arinuence oof emissionunchangedreview of 2aeration is aa result of aMany situatsoil aerationgreater N2Othe small net al., 1999;et al., 2007and Alakukzero tillageular year anincreased etrication (with crop resurface incrzero tillageusing soil cresidue treapresence oftional tillagUnder labosoils were btillage. Duesion are sigwarming poloss in soil C

One migunder redubut publishregion of Fiuxes weregated soils iet al. (2009during the to conventiet al. (2009but conven

3. Organic

3.1. Generic

In assesincreasing S

1. The magcation ofhave alreincrease manure.

2. Availabilwill be a

Table 2Typical carbon content of selected organic materials. From: Defra Manure AnalysisDatabase MANDE (DEFRA, 2003; Gibbs et al., 2005; Bhogal et al., 2006).

Manure type Dry matter % Organic C % ds

FYM slurryr littered bio

compcrumb

urcerodue a ll signssed

mulied ttheron. B, for essibi

dditf nit

alys orga

orgaremef mates (eical, mpohin imite, wher Staitedd an08).he med aanue SOtion0 kg

certion

decced r reteecogColeer, ined inloamt of 4ls in Table 3, but is considered a useful way of summarisingta.

Farm manuresle 3 shows a mean annual rate of SOC increase in topsoilsg C ha1 yr1 t1 ds, but with a 5-fold range of 20-100 kg95% condence interval. The wide range results from thece of reduced/zero tillage on nitrous oxide (N2O)om soil

e contradictory reports in the literature regarding thef tillage on N2O emissions from soil. Examples exists from zero tillage soil being increased, decreased or

compared to conventional tillage. It is clear from a5 comparisons (Rochette, 2008) that the state of soil

key factor determining the outcome, and this in turn is combination of soil type, drainage status and rainfall.ions in the UK and northwest Europe fall into the poor

category of (Rochette, 2008) so are more likely to have emission under zero tillage. This is consistent with

umber of direct eld measurements in the UK (e.g. Ball Vinten et al., 2002a; Baggs et al., 2003), France (Oorts), Belgium (Beheydt et al., 2008) and Finland (Reginaku, 2010). Of course, increased N2O emissions under

is not inevitable, but will depend on rainfall in a partic-d its timing with respect to fertilizer N applications, asmissions appear to result mainly from increased deni-Baggs et al., 2003). There is also evidence of interactionssidues: the presence of plant residues at or near the soileases the likelihood of short-term poor aeration under

(Baggs et al., 2003; Ball et al., 2008). Ball et al. (2008),ores taken from eld plots with different tillage andtments, found that N2O emissions were greater in the

cover crop residues in zero tillage compared to conven-e even though there was no difference in bulk density.ratory conditions, N2O emissions from the zero tillageetween 1.5 and 35 times greater than from conventional

to the large GWP of N2O, even small increases in emis-nicant. As pointed out by Rochette (2008), the globaltential of 1 kg of emitted N2O-N ha1 is equivalent to a

of approximately 125 kg ha1.ht expect increased oxidation of atmospheric methaneced tillage in view of the decreased soil disturbance,ed results on this are variable. At six sites in the borealnland Regina and Alakukku (2010) found that methane

negligible and not affected by tillage practice. In irri-n a semi-arid environment in North America, Alluvione) observed signicantly increased methane emissionsgrowing season of maize under zero-tillage comparedonal tillage. By contrast, also in North America, Ussiri) found that zero till soil was a small sink for methanetionally tilled soils were a small source.

material additions

issues on organic material additions.

sing the potential of different organic materials forOC content, three separate issues are relevant:

nitude of the SOC increase obtained from a given appli- each material. For example, composted materials thatady undergone a decomposition process are likely toSOC more than an equal mass of fresh plant material or

ity of different materials. Some, such as farm manures,vailable in large quantities and thus be a signicant

CattleDairy BroileDigestGreenPaper

resoby-pcauslocaasse

3. Howappsoil satianda po

In asions o

3.2. Anon soil

Theare extclass ocentagare typand co

Witals is l(NVZs)Membare limEnglan(S.I., 20First, taveragfarm mpost, thapplica(i.e. 25ble andapplica

Theinuengreatethis is r1996; Howevresentsandy contenintervathe da

3.2.1. Tab

of 60 kin the 25 326 32

60 32solids 25 35ost 65 13le 40 37

at national or regional scale. Other materials may bects of specic processes or industries and, even if theyarge SOC increase per unit mass added, will only be oficance because of the limited quantity available when

at national scale.ch of each material is available in addition to that alreadyo soil? If the majority of a material is already applied toe may be only limited possibilities for improving utili-y contrast, if a material is currently regarded as wastexample, disposed of to landll or burned, then there islity of signicantly greater utilisation.

ion, as with reduced tillage, any impacts on net emis-rous oxide (or methane) must be considered.

is of evidence on impacts or organic material additionsnic carbon using data from UK

nic materials potentially available for application to soilly diverse in their properties (Table 2). In addition, eacherial is inherently variable; the values for organic C per-xpressed on the basis of dry solids, ds) shown in Table 2but a wide range can occur, especially for farm manuressts.the EU, the application rate of many organic materi-d by their N content. Within Nitrate Vulnerable Zonesich now cover over 60% of England and 100% of some EUtes such as Denmark, farm manure total N applications

to a maximum of 170 kg ha1 total N. Additionally, ford Wales, there is a eld N limit of 250 kg ha1 total N

For the materials listed in Table 3 two values are given.ean annual increase in SOC per tonne of material applied,cross all the experimental sites identied. Second, forres, biosolids (treated sewage sludge) and green com-C increase potentially possible (compared to no organic) if applied at the maximum permissible rate in an NVZha1 total N in any 12 month period). For paper crum-eal straw, potential SOC increases are shown for typical

rates.omposition rate of added organic materials is greatlyby soil type in addition to environmental factors, withntion of added C in soils having a higher clay content;nised in models such as RothC (Coleman and Jenkinson,man et al., 1997) and CENTURY (Parton et al., 1993).

this review, results are averaged over all soil types rep- the experiments; for most materials these ranged froms with a clay content of 5% to clay loams with a clay3%. This averaging contributes to the large condence

D.S. Powlson et al. / Agriculture, Ecosystems and Environment 146 (2012) 23 33 27

Table 3Potential increases in SOC in topsoils following the application of a range of organic materials at 250 kg ha1 total N.

Organic material Number of sites Application rate ofdry solidsa

SOC increaseb References

t ha1 yr1 t1 dry solids For maximum permittedapplication rate in UK NitrateVulnerable Zonesa

kg ha1 yr1

Farm manures 8 10.5 60 20 (20100) 630 Mattingly et al. (1975),Jenkinson and Johnston(1977), Jenkinson (1990),Bhogal et al. (2006, 2007)

Digested biosolids 10 8.3 180 24 (130230) 1500 Johnston (1975), Gibbset al. (2006)

Raw sewage sludge 10 130 20 (90170) Johnston (1975), Gibbset al. (2006)

Green compost 4 23 60 10 (4080) 1400 Wallace (2005, 2007)Paper crumble 30c (60) d 1800Cereal straw 4 7.5e 50 15e (2080) 375 Nicholson et al. (1997),

Smith et al. (2008),Johnston et al. (2009),Powlson et al. (2011a)

a Rate to supply 250 kg N ha1, maximum permitted under Nitrate Vulnerable Zone regulations in England and Wales (S.I., 2008).b Mean standard error with 95% condence interval in parenthesis.c Expressed on fresh weight basis. Typical application rate of primary or secondary chemical/physically

total N (Gibbs et al., 2005).d Average SOC increase per tonne dry solids assumed to be the same as for farm manures.e Expressed

contrastingfering duraThe mean v(>49 years othe mean analso includeFYM, cattleannual SOCmean valuethan the valpean experi(2004). Thitained a larthe currentin relation equilibrium

The trentime is illuexperiment

Fig. 1. Annuaamounts and kover which the

006,bout

had mostere

incra1

g towon etitteppli

applent w

trenc ma

Fig. ment per t fresh weight of straw. Taken as typical application rate.

materials used in the experiments reviewed, the dif-tions of the experiments, and the different soil types.alue includes data from three long-term experimentsf applications) with farmyard manure (FYM): in thesenual SOC increases were 10-22 kg C ha1 yr1 t1 ds. Its a set of newer experiments (8-25 years) that included

slurry and broiler litter (Bhogal et al., 2006, 2007) with increases in the range 30-200 kg C ha1 yr1 t1 ds. The

in Table 3 of 60 kg C ha1 yr1 t1 ds is rather higherue of 20 kg C ha1 yr1 t1 ds derived from a set of Euro-ments reviewed by Freibauer et al. (2004) and King et al.s is almost certainly because the earlier reviews con-ger proportion of longer-running experiments than in

study and because rates of storage of organic carbonto inputs decline as total SOC content approaches an.d for a decreasing rate of annual SOC increase over

et al., 2after aslurry)was alsite whrate of10 kg hmovinJohnstwas omyears awhilstconsist

Theorganidata inExperistrated in Fig. 1, based on results from 15 of the 16s with manures reviewed in the current study (Bhogal

l change in topsoil SOC per year as a result of adding the differentinds of organic matter shown in Table 3 and as a function of the time

additions were made.

shown as Cadjusted fo23 cm) on psubsoil C dparable ove(FYM) each

0

20

40

60

80

100

1820

Org

anic

C in

soi

l(t

C h

a-1 )

Fig. 2. Change(FYM) annuall(), includingcontrol (). So treated paper crumble = 75 t ha1 fresh weight, supplying 150 kg ha1

2007). The annual rate of SOC increase declined sharply 20 years. At two sites where manures (pig FYM or pigbeen applied for only 8 years, the mean annual increase

200 kg ha1 yr1 t1 ds. At the other extreme, for thecattle FYM had been applied for 144 years, the annualease (averaged over the entire period) had declined toyr1 t1 ds. This is consistent with the concept of soilsards a new equilibrium SOC content as discussed by

al. (2009). The result from one treatment at one sited from Fig. 1 because it appeared spurious: after 10cation of cattle slurry SOC had apparently decreased,ication of cattle FYM at the same site led to an increaseith results from other sites.

d for SOC to move towards a new equilibrium value asterials are applied is also illustrated by the long-term2. This shows the most recent data from the Broadbalk

at Rothamsted, UK, showing data up to 2005. SOC is

stock, expressed in t C ha1, not as % C. The data werer observed decreases in the bulk density of topsoils (0-lots given FYM, by including the appropriate amount ofirectly below 23 cm, to ensure soil weights were com-r time. For the treatment receiving farmyard manure

year, starting in 1843, SOC content increased rapidly

2020200019801960194019201900188018601840Year

Farmyard m anure annually

Unmanured

NPK

FYM ann uallysince 188 5

s in SOC (023 cm) on Broadbalk, for plots given Farm Yard Manurey since 1843 () or 1885 (), and those given mineral fertilisers only

N, P and K at 144, 35 and 90 kg ha1 respectively, and the unmanuredlid lines derived from RothC model.

28 D.S. Powlson et al. / Agriculture, Ecosystems and Environment 146 (2012) 23 33

until about 1920, though the most rapid increase was during therst 20 years. Taking output from the RothC simulation in Fig. 2,the average annual rate of SOC increase during the rst 20 yr ofFYM application was 1.0 t ha1 yr1; during the nal 20 yr the cor-respondingperiod 1926year in vecontent in areceiving Ftrolled by hresumed bulibrium valuof SOC incrless. The sastarted in 1receiving Fsted whereyear, but withe increasediminishing

3.2.2. BiosoThe me

tion of dige180 kg C ha

sponding vadegree of ddigestion prless decompraw sewageland in the Uments, is slit1 dry solition during

As with masks a wthe experimtal sites and80 kg C ha1

ment (Johnto a sandy lyears of appet al., 2006)90 to 290 kincrease in in low claycompared tclay.

The mea90 kg C ha1

result of threview. Butthat of 300 (2004). Thecations wit1500 kg C hthan the av34 years at2009). The prising becaarea that haat a very low

3.2.3. GreenThis ma

prunings an

has increased greatly over recent years as municipal authoritieshave sought to minimise the amount of organic material disposedof in landll. In 2003-4 it was estimated that 480,000 t (freshweight) of compost was recycled to agricultural land in the UK

ostin 200en co

Resus) sh

(Tab ha

Ros es oe peanuhe is mod in twic

addtion

Papeer crpri

nnoteighd andes inata d verume simnd 30

and 7 per ts beeent st, thon a

Cerea me1 fre1 dexperraw ; metraw2009al ad, espwas aller

C hat fres

abouoratiions

a tre is ureatmin ren et annual rate had slowed to 0.2 t ha1 yr1. During the-1966 all plots on Broadbalk were bare-fallowed one, to control weeds. This led to a small decline in SOCll treatments, but is most clearly seen in the treatmentYM. After fallowing ceased (because weeds were con-erbicides) the increasing trend in the FYM treatmentt at a slower rate as the soil tended towards a new equi-e. If the soil had not had fallow years, the annual rateease in latter years would almost certainly have beenme trend can be seen in the later FYM treatment that885. It is also clear in similar data from the treatmentYM annually in the Hooseld Experiment at Rotham-

spring barley rather than winter wheat is grown eachth no fallowing (see Johnston et al., 2009). On Hooseld

in SOC in the FYM treatment has continued, albeit at a rate, for about 130 years.

lidsan annual rate of SOC increase from the applica-sted biosolids, in the experiments reviewed here, is1 yr1 t1 ds (Table 3). This is three times the corre-lue for farm manures, presumably reecting the greaterecomposition that has already occurred during theocess: the organic C in biosolids, when applied to soil, isosable than that in farm manures. The mean value for

sludge, which is no longer permitted to be applied toK (ADAS, 2001) but was included in some of the experi-ghtly lower than for digested sludge (130 kg C ha1 yr1

ds; Table 3), reecting the lesser degree of decomposi- treatment.farm manures, the mean value for annual SOC increaseside range of values, inuenced by the length of timeents have continued, the soil types at the experimen-

the rate of application. The mean includes a value ofyr1 t1 ds from the Woburn Market Garden Experi-

ston, 1975) where digested sewage sludge was appliedoam soil for 18 years. It also includes data after only 4lication in a network of nine newer experiments (Gibbs. In these, the annual rate of SOC increase ranges fromg C ha1 yr1 t1 ds, again reecting the faster rate ofthe early years and also the lower SOC accumulation

soils: 90 kg C ha1 yr1 t1 ds at a site with 8% clayo 280-290 kg C ha1 yr1 t1 ds at sites with 23 or 30%

n value for biosolids in Table 3 is larger than that ofyr1 t1 ds derived by King et al. (2004), probably a

e greater predominance of longer-term data in their it is not clear why our value is considerably lower thankg C ha1 yr1 t1 dry solids derived by Freibauer et al.

annual SOC increase achievable from biosolids appli-hin the maximum rate permitted in NVZs in the UK isa1 yr1 (Table 3). For comparison, this is slightly lowererage annual rate of 1700 kg C ha1 yr1 measured over

non-experimental sites in North America (Tian et al.,higher rate over a long period in that study is not sur-use biosolids were being used for the reclamation of and been subject to strip mining, so soil at the site started

SOC content.

compostterial is derived from composting grass cuttings, treed leaves from gardens and parks. The quantity produced

(Comppost inof gre2007).(3 sitet1 ds70 kg Cyears (manurever thfarm mThus, tareas iretaineabout ing theproduc

3.2.4. Pap

try, comthat cafresh wEnglanincreasyears dshowePaper cto hav(20% aC (80%in SOCthis haN contcompolarger

3.2.5. The

yr1 t

yr1 t

four eand stweightsince set al., materiditionsstraw ally sm(375 kgof 7.5 rate ofincorpconditclearlychangestraw tfound Powlsog Association, 2005), this has risen to 1.3 M t of com-7-8 (AfOR, 2009). The only data available on the impactmpost on SOC in the UK is that of Wallace (2005,lts after 8 years of applications (1 site) and 5 yearsow a mean annual SOC increase of 60 kg C ha1 yr1

le 3). This is similar to the annual rate of increase of1 yr1 t1 ds found in an experiment in Austria after 12et al., 2006). It is also similar to increases from farmn the basis of SOC increase per tonne applied. How-rmissible application rate in NVZs is greater than forres because of the lower N content of green compost.ncrease in SOC that is practically achievable in manyre than twice that from farm manures (Table 3). The Csoil in these experiments is 23% of the organic C applied,e the corresponding value for farm manures, reect-itional decomposition occurring during treatment and.

r crumbleumble is a waste product from the paper making indus-sing bres derived from the wood used for making pulp

be used in paper manufacture. Around 700,000 tonnest (FW) of paper crumble is applied to agricultural land in

Wales (Gibbs et al., 2005). As yet, there is no data on the SOC produced by this material in the UK, though twofrom experiments with paper mill residues in the USAry large SOC increases (Foley and Cooperband, 2002).ble and farm manures were found by Bhogal et al. (2007)ilar contents of C in recalcitrant lignin-type material% of total C, respectively) and of readily decomposable0%, respectively). Thus, it seems likely that the increaseonne material applied will be similar to farm manures:n assumed in Table 3. However, paper has a very low

compared to farm manures. Accordingly, as for greene actual increase in SOC that is practically achievable isper hectare basis.

l strawan value for SOC increase in Table 3 is 50 kg C ha1

sh weight of straw, similar to the value of 70 kg C ha1

rived by Smith et al. (1997). It represents data fromimental sites with contrasting texture (6-24% clay)application rates ranging from 4 to 18 t ha1 freshasurements were taken at between 6 and 17 years

incorporation began (Nicholson et al., 1997; Johnston; Powlson et al., 2011a). As with the other organicditions, the range of values reects the range of con-ecially soil type. At sites where more than one rate ofreturned, the increase per tonne of straw was gener-

for the higher rate. The mean annual increase in SOC1 yr1; Table 3) for a typical straw application rateh weight ha1 yr1 is slightly smaller than the annualt 500 kg C ha1 yr1 observed over 8 years from strawon at an experiment in Ireland under similar climaticto the UK (van Groenigen et al., 2011). Although there isnd for cereal straw addition to increase SOC, the rate ofsually small and differences between with and withoutents in experiments are often not signicant: this was

views of such experiments by Lemke et al. (2010) and al. (2011a).

D.S. Powlson et al. / Agriculture, Ecosystems and Environment 146 (2012) 23 33 29

4. Discussion

4.1. General issues regarding management impacts on soilorganic carbon content

In sum(Tables 1 aon an annupermits coapproach hstated abovlinear rate ione equilibequilibriumtem, organiis a balanceThus, if a chmaterial adincrease wias the newto no furthin relation any managIt is essentiaccount in a

4.2. Impactgreenhouse

Taking tspective ofzero, gives to conventibut with a value is sliget al. (2005estimate us140 kg C ha

280 kg C ha

ably consisin the long Hamel (200and combinbenecial fotypes.

Accordin(030 cm) oa mean anncurrent valuland in Engtotal SOC stC (using thThis increasequivalent thttp://wwwligible. Howof arable lanalready und

If, as a SOC increahalf the inc150 kg C1 hconversion in England 14.4. But evfor two rea

difcult to apply on many soil types in the UK and northwest Europedue a combination of soil type (especially poorly structured soils)and the largthe amoun

ields in thtrol wy to

the ents l and

that ulatiin roong-theasnd th009)ng (3creang tovels rs arais oning arnateto ans con

undeoss fs onf thed to cludto reprop

(i.etratiadditgas eventi

GlenggesJ ha

tivelyd 30ion oing t of losultingh noconsues ththe

signUK osion

and ssioned Nyearsmakes onsionme e.marising data from numerous experimentsnd 3) we have expressed rates of increase in SOCal basis, i.e. as kg C ha1 yr1. This is convenient andmparisons between management practices, but theas clear limitations that must be taken into account. Ase in Section 3.2.1, SOC does not increase or decrease at an response to a change in management, but moves fromrium level to another over a period of years. The actual

value is a function of soil type, climate, cropping sys-c matter inputs and a range of management factors, and

between rates of organic inputs and decomposition.ange in management such as reduced tillage or organicdition causes an increase in SOC content, the rate ofll be more rapid in the early years and then decrease

equilibrium value is approached, eventually leadinger increase. This is clearly illustrated in Figs. 1 and 2to farm manure applications, but is equally valid forement change as discussed by Johnston et al. (2009).al that the nite nature of SOC increases is taken intony consideration of soil C sequestration.

s of reduced/zero tillage on SOC and overallgas emissions

he value for SOC increases in Table 1 at face value, irre- whether or not they are signicantly different froman annual increase in SOC under zero tillage comparedonal cultivation of 310 kg C ha1 in the 030 cm layer,large standard error (180 kg C ha1; see Table 1). Thishtly lower than the best estimate suggested by Smith) of 400 kg C ha1 yr1, but higher than the more recented in the Stern Report for cool-moist climates (mean1 yr1, with a suggested range of between zero and1 yr1; Stern, 2006; Smith et al., 2008). It is reason-tent with the tendency for a small SOC accumulationterm under zero tillage noted by Angers and Eriksen-8). This small increase, concentrated near the surfaceed with other changes caused by zero tillage, may ber soil quality and functioning on some, but not all, soil

g to Bradley et al. (2005) the mean SOC contentf arable soils in England and Wales is 70 t C ha1 soual increase of 310 kg C ha1 would represent 0.4% ofes. If this increase could be achieved on all the arableland and Wales, and was continued for 10 years, theock in these soils would increase from 361 to 375 Tge values for SOC stock given by Bradley et al., 2005).e of 1.4 Tg C yr1 (equivalent to 5.1 Tg CO2-eq yr1) iso 0.8% of annual UK emissions (635 Tg CO2-eq yr1; see.theccc.org.uk/topics/uk-and-regions), and so not neg-ever these are very optimistic assumptions as only 50%d is currently under conventional cultivation with 43%er reduced tillage (Anon, 2006).rst approximation, it is assumed that the annualse from converting reduced tillage to zero tillage isrease for conventional to zero tillage conversion (saya1 yr1) the SOC increase over 10 years from a total(i.e. both conventionally and reduced tilled arable landand Wales) to zero tillage would be 10.3 Tg instead ofen this increase is unlikely to be realised in practicesons. First, experience has shown that zero tillage is

crop yis usedto conis likelduringsuremthe soiseemsaccumtion is as in lin soutgrass aet al., 2croppionly incroppiSOC le(2 yearThere ica givin altepared authorinputsing acrsystemmost oreleasewe contillage are apEuropeseques

An house to conations.data su2393 Mrespec130 anreductcontaina resulSOC realthoudiesel practic

On expectin the conclunomicin emiincreassome ate to practicsoil eroto assunegative quantities of straw on the soil surface compared witht more common under drier conditions, with smaller, in North America. Second, even when reduced tillagee UK, it is usual for farmers to plough every 3-4 years,eeds and relieve soil compaction. This periodic tillage

cause a loss of at least part of the carbon accumulatedperiod under zero tillage, but there are no direct mea-of the net result of this mix of tillage treatments under

climatic conditions of northwest Europe. However, itthe rate of loss of SOC is generally greater than its rate ofon (Freibauer et al., 2004). A somewhat analogous situa-tations of arable crops with short periods of grass, sucherm ley-arable experiments on contrasting soil typest England, where soil C increases under the periods ofen declines after ploughing for arable crops (Johnston. On a silty clay loam soil, after 24-27 years of ley-arable

years grass/clover, 3 years arable), SOC (0-23 cm) wassed by c.15% (from 15.7 g kg1 under continuous arable

18.1 g kg1 in the ley-arable system). On a loamy sand,emained constant over 30 years of a ley-arable rotationble, 1 year grass ley undersown in the preceding cereal).e study from a maize-soybean rotation in North Amer-n indication that so-called biennial tillage (ploughing

years) led to a larger SOC increase than zero-till com-nual ploughing (Venterea et al., 2006). However, thecluded that this probably resulted from decreased Cr zero-till due to lower yields with this system. Read-rom these studies to the effect of rotational ploughing

SOC, it would not seem unreasonable to conclude that extra C stored during years under zero tillage will bethe atmosphere as CO2 when the soil is ploughed. Thuse that converting the area currently under conventionalduced or zero tillage, using agronomic practices thatriate for the climatic conditions in UK and northwest. rotational ploughing), would lead to little additionalon of soil C.ional benet of reduced tillage, of relevance to green-missions, is the decreased use of tractor fuel comparedonal cultivation due to the decreased number of oper-dining et al. (2009, supplementary material 1) quoteting that conventional seed-bed preparation requires1 and reduced and zero tillage 1868 and 418 MJ ha1,; in turn these are equivalent to emissions of 166,

kg CO2 ha1, respectively. Watts et al. (2006) found af 11% (10 kPa) in the specic draught (S) between plots1.1% SOC compared with plots containing 0.89% SOC asng-term management. Reductions in S on plots with 3%g from long-term applications of FYM were better still,t spectacularly so (18%). Similar modest reductions inmption and thus CO2 emissions may be expected fromat enhance SOC.basis of the above considerations it is unrealistic toicant climate change mitigation from reduced tillager northwest Europe. The main factors leading to thisare: (a) very small accumulation of SOC under the agro-climatic conditions of the region; (b) the small savingss from fuel used for tillage operations; (c) the risk of2O emissions under reduced/zero tillage, at least in, as described in Section 2.4. It would be appropri-e decisions on the application of reduced/zero tillage

the basis of other considerations (e.g. reduced risk of, other soil quality issues, labour and cost factors) andno major impact on climate change, either positive or

30 D.S. Powlson et al. / Agriculture, Ecosystems and Environment 146 (2012) 23 33

4.3. Impacts of organic material additions on SOC and overallgreenhouse gas emissions

Table 3 shows the increases in SOC, on a per hectare basis, fora range of appear largtial for C seqgenuinely cfactors musmaterial avcurrently uother than requiremen

In the cWilliams etmanures armanure proSOC shownto be utilisaccumulatiand contribstock. One eburned for eduction). Anor depositelikely that pof grasslandsoil. Hopkingrassland sUK, both ofin the treatonly slightlGrass) that SOC storageon grasslancurrently lolimitations

Similarlyduced in th(77%) is ap(mostly witapplicationincreasing tand Wales 2008). Aboumajority ofsequently insoil. Of couring the prodbe returnedrated. But thand then aand Turley not utilised(40,000 t) aThe proporteration schit appears tapplied to sutilisation aative impacfor any majPowlson et

Two mabe utilised 480,000 t fr

Composting Association (2005); this has risen to 1.3 Mt of com-post in 20078, AfOR report (2009)) and paper crumble, a wasteproduct from the paper-making industry of which 700,000 t (freshweight) was recently estimated to be applied to agricultural land

et alely s

a mties tty ofater

incr the etailpar

be vl dispundempa

havel is ca

ner. Th

clim to b, whehar y onict

secoal adnic Ndirece chaat a rndivicrumcreahighing

abovreenals, itentie nore h the

litteer, astanlurryferti

ha

gest welt). Tnetmn DYM, t inct com1 yr

and bcomplurryd inject organic material additions. Supercially these valuese and might be taken as indicating a considerable poten-uestration. However, to assess the extent to which theyontribute to climate change mitigation, a range of othert be considered. In particular: (1) the quantities of eachailable at national scale, (2) the extent to which they aretilised, and (3) impacts on uxes of greenhouse gasesCO2, in particular N2O through effects on N fertilizerts and N losses.ase of farm manures, large quantities are available:

al. (2000) estimated that 90 Mt (fresh weight) of farme produced in the UK. However, virtually all of theduced is already applied to soil. Thus, the increases in

in Table 3 cannot be regarded as additional C storageed in a new strategy to mitigate climate changethison of SOC has already occurred or is currently occurringuting to the maintenance of the present national SOCxception is the ca. 580,000 t of poultry litter currentlylectricity generation (less than 1% of total manure pro-other likely exception is manure currently applied to,d on, grassland soils that are already high in SOC. It isart of the organic C in manure deposited on the surface

soil will decompose to CO2, leaving little residue in thes et al. (2009) provide some evidence for this from oldoils in the Palace Leas and Park Grass Experiments in

which have continued for over 100 years. SOC contentments receiving farmyard manure for long periods wasy greater than (Palace Leas) or no different from (Parkin the controls not receiving manure. Thus total national

could probably be increased if the manure now spreadd soils were transported to areas of arable land that arew in SOC. However, there are obvious logistical and costto such a strategy., it is estimated that 1.4 Mt biosolids ds is currently pro-e UK (Water UK, 2010). It is estimated that ca. 1 Mtplied to agricultural land, a further 16% is incineratedh energy recovery). Thus there is little scope to increases to soil and increase the contribution of biosolids tohe UK SOC stock. Annual straw production in Englandis estimated at about 11.4 Mt (Copeland and Turley,t 50% of this is returned directly to soil, with the vast

the remainder being used as animal bedding and sub- production of farmyard manure, and then returned tose, signicant decomposition of straw C will occur dur-uction of farmyard manure, so less straw-derived C will

through this route than if straw was directly incorpo-e practical benets from using straw as animal bedding,s a component of manure, are very strong. Copeland(2008) estimate that less than 2% of straw is currently

in agriculture: a combination of mushroom productionnd 200,000 t currently burned for electricity generation.ion could rise to about 10% if plans for new power gen-emes are realised. Thus, with both biosolids and straw,hat the vast majority of these materials are currentlyoil, in some form, leaving very little scope for additionals a strategy to increase SOC stocks. The potentially neg-ts on soil quality of removing larger quantities of strawor expansion of its use in bioenergy were discussed byal. (2011a).terials that are relatively new and are beginning tofor soil application are green compost (estimated thatesh weight was recycled to agricultural land in 20034,

(Gibbsrelativpost isquantiquantithese mtion towithin

A dll comwouldlandloccur Any cowouldlandl

Onebiochaperatewhichstocksin biocstabilitthe con

Themateriinorgaand inof theseither in an ipaper

If into be increascussedfrom gmaterithe poThus thG), is m

Witbroilerfertilizare subDairy sing to CO2-eqthe laring, asindirecthe bein coluWith Fthe nebeneeq ha

slurry green dairy sreplaceare sub., 2005). Although the use of paper crumble is limited tomall areas close to paper-making factories, green com-aterial that is likely to become available in increasinghroughout Europe as part of attempts to decrease the

organic material disposed to landll. The application ofials to soil could be regarded as a genuine new contribu-easing SOC storage, and thus mitigating climate changenite limits possible from soil C sequestration.ed assessment of C losses and stabilisation from landed to aerobic composting followed by land applicationaluable, but is beyond the scope of this paper. Withosal at least part of the decomposition process willr anaerobic conditions, leading to methane emission.rison of the climate change impacts of the two processes

to take account of the extent to which methane fromptured and utilised.w material that we have omitted from this review isis is because, as yet, there are no studies under the tem-ate and soil types of the UK or northwest Europe onase any assessment of its potential to increase soil Cther through accumulation of C in a very stable formitself or through a mechanism of conferring enhanced

other forms of organic C. Powlson et al. (2011c) discussing evidence on biochar impacts on soil C.nd major issue to be considered is the impact of organicditions on the N cycle, through partial replacement of

fertilizers and either decreases or increases in directt emissions of N2O. Table 4 brings together estimatesnges for a range of different organic materials applied

ate containing 250 kg N ha1 (the maximum permissibledual eld under UK NVZ regulations) or (in the case ofble) a typical application rate.sed SOC storage is included, all organic materials appearly benecial in leading to a CO2 emission saving bythe SOC stocks (Table 4, column F). However, as dis-e, most of the materials are already fully utilised, apart

compost and paper crumble. So, apart from these twot is incorrect to include SOC increases when assessingal for new contributions to climate change mitigation.al column in Table 4, that excludes SOC change (columnrealisticand an order of magnitude smaller.

three farm manure examples (cattle FYM, dairy slurry,r) which all supply crop-available N, the saving in Nnd hence the emissions from N fertilizer manufacture,tial (180300 kg CO2-eq ha1 yr1; Table 4 column C).

and broiler litter supply the most crop available N, lead-lizer N savings of about 80 kg N ha1 yr1; 270300 kg1 yr1). But these materials are also expected to givelosses of N through ammonia volatilisation and leach-l as the largest resultant emissions of N2O (direct andhese manure-associated emissions partially counteract

from replacing N fertilizerhence the negative values of Table 4, indicating a net increase in N2O emissions.

where N is less readily available and less subject to loss,rease in N2O emission is much lower and the overallpared to no manure use is greater (almost 300 kg CO2-1), compared to about 100 kg CO2-eq ha1 yr1 for dairyroiler litter (Table 4, column F). Digested biosolids andost both provide somewhat less crop available N than

and broiler litter, and thus less saving of emissions fromorganic N fertilizer use (Table 4, column C). But they alsoto smaller N losses, and thus smaller N2O emissions, so

D.S. Powlson et al. / Agriculture, Ecosystems and Environment 146 (2012) 23 33 31

Table 4Net changes in greenhouse gas emissions resulting from application of various organic materials.

Organic material Applicationratea

Crop availableNb

CO2-eq saving fromfertilizer

Net CO2-eqchanges in N2O

d

Net CO2-eq changedue to SOC

Net CO2-eq savingf

Cattle FYM (Dairy slurry Broiler litterDigested bioGreen compPaper crumb

a Quantity c VZ reb Quantity o ount

data in DEFRAc Saving in e lumn B

from N2O emid Net result ciated

but for all mat plus ibut it is unrea d.

e Using SOCf Net result columg Negative v mble.h Not correc

their overalas farm man

As was aalready beials associatThus they calready accals. Thus evfarm manuN cycle (Tachange mitifor additionused and th

Paper crals. It causerate but, beadditional Nof soil-derivattribute a to this applimpact is aneq ha1 yr

crumble cosoil mineraand resultinbe conductthat accom(2002b) fouC and glucthis N wasical applicacellulose, wat laborato60 kg N ha

needed herremobilisatsation of pincreases inmate chang

alte

clus

rall nal ing ctionf orghe ced Se so

moifounmanufacturec emissions

A B C D

t or m3 ha1

fresh weightkg ha1 CO2-eq, kg ha1 yr1

Fresh) 42 50 180 110 83 85 305 185

8 75 270 185 solids 33 35 125 55ost 36 15 55 55le 75 60g 215 370 ontaining 250 kg N ha1 (i.e. maximum permissible individual eld rate under UK Nf N estimated to become available to a crop in the year of application, and hence am, 2010).missions from N fertilizer manufacture from decrease in N fertilizer use shown in cotted from manufacture of ammonium nitrate (Flynn and Smith, 2010).of (a) decreased emissions from decreased rate of N fertilizer and (b) emissions assoerials used emission factor of 1.25% instead of currently recommended value of 1%listic to attempt more precise estimates in view of wide range of material considere

values from Table 3.of emissions changes in earlier columns either including (column F) or excluding (alue because additional N fertilizer at 60 kg N ha1 typically applied with paper crut to include except for green compost and paper crumblesee text.

l impacts (excluding SOC changes) are of the same orderures (Table 4, column F).rgued for SOC changes, farm manures and biosolids areng used, so the emissions savings from these materi-ed with changes in the N cycle are already occurring.annot be counted as new savings, but show the benetsruing through the utilisation of these organic materi-en the annual savings of about 80300 kg CO2-eq fromres and biosolids resulting from their impacts on theble 4, column G) do not represent additional climategation. Only with green compost is there a real potentialal mitigation because of the small quantities currentlye scope for a substantial increase.umble is a special case compared to the other materi-s the largest increase in SOC when applied at a typicalcause it contains very little N, it is customary to apply

on theland.

5. Con

Oveadditioincreasapplications o

In tincreasnear thof thisso far fertilizer to counteract the expected immobilisationed mineral N. The additional N fertilizer requires us tolarge increase in total greenhouse gas emissions (N2O)ication. Thus, if SOC changes are excluded, the overall

increase in greenhouse gas emissions of >500 kg CO2-1 (Table 4). On the other hand, autumn applied paperuld potentially be used as a means of immobilisingl N and decreasing over-winter nitrate leaching lossesg indirect N2O emissions. Additional studies should

ed to test whether the current additions of N fertilizerpany paper crumble are really necessary. Vinten et al.nd between 1 and 7 mg N immobilised g1 cellulose-ose-C respectively added to laboratory soils. Most of

remobilised within 6 weeks. At 1 mg N g1 C, a typ-tion of paper crumble (Tables 3 and 4), if similar toould appear able to lock up 11 kg N ha1 for 6 weeksry temperatures. This is substantially less than the1 typically applied (footnote to Table 4). More work ise because, as Whitmore and Groot (1997) have shown,ion of nitrogen depends on soil type. If further utili-aper crumble or similar materials were possible, the

SOC achieved could be regarded as additional cli-e mitigation giving a net positive impactdepending

reduced tilsmall incretillage, it seinversion tiessary in thand Wales tillage), andbe unsuitabin this regio

In the cmore compin largest qalready utisoil is alreafor increaseearlier in tof these marequiremenemissions (materials tmaterials aitive and ncannot be cincreasee

Includingh SOCchange

Excluding SOCchange

E F G

2310 2600 2901100 1220 1201065 1150 855500 5680 1805130 5240 1106600 6015 585

gulations). For paper crumble, typical application rate. by which inorganic N fertilizer application may be decreased (using

. Mainly CO2 from the energy used in manufacture, but a contribution

with organic materials. Based on emissions factors from IPCC (2006),ndirect emissions. This makes some allowance for indirect emissions

n G) changes in SOC content.

rnative fate of the material if it were not applied to

ions

we conclude that there is very limited scope forclimate change mitigation in England and Wales byarbon stocks in agricultural soils, either through greater

of reduced or zero tillage or through increased applica-anic materials to soil.ase of reduced tillage this is because the evidence forOC stock (as opposed to an increased SOC concentrationil surface) is highly questionable, at least in the climatest temperate region and with the agronomic practicesd appropriate. A specic issue is the need to combine

lage with periodic inversion tillage: even if there is aase in SOC stock during the period of reduced or zeroems virtually certain that this will be lost as a result ofllage in the rotational ploughing system found nec-e region. In addition, as 43% of arable land in Englandis already under reduced tillage (with 7% under zero

practical experience has shown which soils appear tole for these practices, the scope for further expansionn is limited.ase of additions of organic material the situation islex. A major factor is that the materials availableuantities (farm manures, cereal straw, biosolids) arelised to a very large extent. Their existing addition tody maintaining SOC stocks and there is very little scoped utilisation. A few exceptions have been discussedhe paper. In addition to impacts on SOC, utilisationterials is benecial from the viewpoint of decreasingts for N fertilizer, thus saving fertilizer-associated GHGprovided the offsetting impact of N2O from the organichemselves is taken into account). But, again, as thesere already largely utilised, the N-related impacts (pos-egative) are already part of the national budget andounted again. However, there is much evidence that the

32 D.S. Powlson et al. / Agriculture, Ecosystems and Environment 146 (2012) 23 33

N derived from organic materials could be utilised more efcientlywith signicant benets for N-related emissions. We concludethat a key exception to this negative result is the utilisation ofgreen compost derived from household and municipal sources.Much of thpreviously tribute to amitigation priate to enmeasures tohealth throThe carbonweigh the m

Acknowled

We acknRural Affairsupport undable Soil FunWallace for

References

Abiven, S., Mesoil aggreg112.

ADAS, 2001. leticket=

AfOR, 2009. T2007/8 Re

Alluvione, F., Htion effectsystems. Jo

Alvarez, R., 20soil organi

Angers, D.A., EdistributioJournal 72

Anon, 2006. FaAffairs.

Baggs, E.M., Stoxide emiconventio

Baker, J.M., Ocsequestratment 118,

Ball, B.C., Crichand CO2 space, com

Ball, B.C., Frankexperimenof the Inte757762.

Ball, B.C., Scottillage, com2939.

Beheydt, D., Boventional

Bhogal, A., Nicquality. DI

Bhogal, A., Nicsoil bio-phsium, Poit

Bhogal, A., Nicon soil bioScience 60

Blair, N., Faulimpacts oand Tillage

Blanco-Canquon-farm as

Boddey, R.M., and soil-prety of Ame

Bradley, R.I., Mand land u363369.

Cannell, R.Q., Finney, J.R., 1973. Effects of direct drilling and reduced cultiva-tion on soil conditions for root growth. Outlook on Agriculture 7, 184189.

Chaney, K., Hodgson, D.R., Braim, M.A., 1985. The effects of direct drilling,shallow cultivation and plowing on some soil physical-properties in a long-

exp133.., Ngly strunal 74, K., Jeil. In:ter Mo372, K., Je

Richtrimenting Apostind, J., T

in G, p. 17003. 006, h010.

he car.C., Smgationilizer S.J., Cocarbo209t, 201t OfcP., Raman, J.,and, RIn: Soor, M.tributirnmeed Kinbberson: an687.r, A., Re agri., Muigricules Scie.A., ChCampeld ss conting, M.T.A.P.

agric, D.W, 2009s in thnt dec06. Aga K., Nse Gasrammn, D.STransa368.n, D.Sey Exp01., A.E.

cts of ssium131., A.E.,ainabl

Elsev.J.A., Tking Gil OrgctoratThem., Brang po

in Ene material used to generate this type of compost wasdisposed to landll, so any applications to land con-

genuine increase in SOC stock and thus climate changethrough additional C sequestration. It is clearly appro-courage developments of this nature, of course taking

minimise any negative impacts on soil quality or publicugh inclusion of undesirable materials in the composts.

cost of transport of moving compost is unlikely to out-itigation potential (Smith and Smith, 2000).

gements

owledge the UK Department for Environment, Food ands (Defra) for funding for project SP0561and BBSRC forer the institute strategic programme grants on Sustain-ction and Bioenergy and Climate Change. We thank Phil

making available data on green compost.

nasseri, S., Chenu, C., 2009. The effects of organic inputs over time onate stabilitya literature analysis. Soil Biology and Biochemistry 41,

The Safe Sludge Matrix. http://www.adas.co.uk/LinkClick.aspx?f CX7x v4nY%3d&tabid=211&mid=664,08/09/2011.he State of Composting and Biological Waste Treatment in the UKport EVA 017. Association for Organics Recycling.alvorson, A.D., Del Grosso, S.J., 2009. Nitrogen, tillage, and crop rota-s on carbon dioxide and methane uxes from irrigated croppingurnal of Environmental Quality 38, 20232033.05. A review of nitrogen fertilizer and conservation tillage effects onc carbon storage. Soil Use and Management 21, 3852.riksen-Hamel, N.S., 2008. Full-inversion tillage and organic carbonn in soil proles: a meta-analysis. Soil Science Society of America, 13701374.rm Practices Survey 2006. UK Department for Environment and Rural

evenson, M., Pihlatie, M., Regar, A., Cook, H., Cadisch, G., 2003. Nitrousssions following application of residues and fertiliser under zero andnal tillage. Plant and Soil 254, 361370.hsner, T.E., Venterea, R.T., Grifs, T.J., 2007. Tillage and soil carbonionwhat do we really know? Agriculture Ecosystems and Environ-

15.ton, I., Horgan, G.W., 2008. Dynamics of upward and downward N2Ouxes in ploughed or no-tilled soils in relation to water-lled porepaction and crop presence. Soil and Tillage Research 101, 2030.lin, M.F., Holmes, J.C., Soane, B.D., 1994. Lessons from a 26-year tillaget on cereals. In: Proceedings of the 13th International Conferencernational Soil Tillage Research Organisation, Aalborg, Denmark, pp.

t, A., Parker, J.P., 1999. Field N2O, CO2 and CH4 uxes in relation topaction and soil quality in Scotland. Soil and Tillage Research 53,

eckx, P., Ahmed, H.P., Van Cleemput, O., 2008. N2O emission from con-and minimum-tilled soils. Biology and Fertility of Soils 44, 863873.holson, F., Chambers, B., 2006. Manure organic carbon inputs and soilAS Report, Plant Production, pp. 3335.holson, F., Chambers, B., 2007. Organic carbon additionseffects onysical and physico-chemical properties. Soil Organic Matter Sympo-iers.holson, F.A., Chambers, B.J., 2009. Organic carbon additions: effects-physical and physico-chemical properties. European Journal of Soil, 276286.kner, R.D., Till, A.R., Poulton, P.R., 2006. Long-term managementn soil C, N and physical fertility. Part 1. Broadbalk experiment. Soil

Research 91, 3038.i, H., Lal, R., 2008. No-tillage and soil-prole carbon sequestration: ansessment. Soil Science Society of America Journal 72, 693701.Jantalia, C.P., Alves, B.J.R., Urquiaga, S., 2009. Comments on no-tillageole carbon sequestration: an on-farm assessment. Soil Science Soci-rica Journal 73, 688689.ilne, R., Bell, J., Lilly, A., Jordan, C., Higgins, A., 2005. A soil carbonse database for the United Kingdom. Soil Use and Management 21,

term125

Chung, HhighJour

Colemanin soMatpp. 2

ColemanP.R.,expe

ComposCom

CopelanstrawYork

DEFRA, 2NT2

DEFRA, 2on t

Flynn, HmitiFert

Foley, Bsoil 2086

Foresighmen

Forster, J., LeDorling. TignCongoveUnit

Franzluetrati686

Freibauein th

Gibbs, Pon aWal

Gibbs, PJ.R., site cake

GlendinK.Wnant

HopkinsA.G.plotrece

IPCC, 20MiwhouProg

Jenkinsoical 361

JenkinsoBarl871

JohnstonEffePota102

Johnstonsust101.

Jones, RWorof SoDireSoil

King, J.Asavisoilseriment on spring barley. Journal of Agricultural Science 104,

o, K.J., Plante, A.F., Six, J., 2010. Evidence for carbon saturation in actured and organic-matter-rich soil. Soil Science Society of America, 130138.nkinson, D.S., 1996. RothC-26.3a model for the turnover of carbon

Powlson, D.S., Smith, P., Smith, J.U. (Eds.), Evaluation of Soil Organicdels Using Existing Long-Term Datasets. Springer-Verlag, Heidelberg,46.nkinson, D.S., Crocker, G.J., Grace, P.R., Klir, J., Korschens, M., Poulton,er, D.D., 1997. Simulating trends in soil organic carbon in long-termts using RothC-26.3. Geoderma 81, 2944.ssociation, 2005. The State of Composting in the UK 2003/2004. Theg Association.urley, D., 2008. National and regional supply/demand for agriculturalreat Britain. Report prepared for the National Non-Food Crops Centre,.Manure Analysis Database (MANDE). Final report to Defra for projectttp://randd.defra.gov.uk.The effects of reduced tillage practices and organic material additionsbon content of arable soils. Scientic Report for Defra Project SP0561.ith, P., 2010. Greenhouse gas budgets of crop production and the

potential of nutrient management. In: Proceedings 670, Internationalociety, York.operband, L.R., 2002. Paper mill residuals and compost effects onn and physical properties. Journal of Environmental Quality 31,5.1. The Future of Food and Farming, Final Project Report. The Govern-e for Science, London.aswamy, V., Artaxo, P., Berntsen, T., Betts, R., Fahey, D.W., Haywood,

Lowe, D.C., Myhre, G., Nganga, J., Prinn, R., Raga, G., Schulz, M., Van., 2007. Changes in atmospheric constituents and in radiative forc-lomon, S., Qin, D., Manning, M., Chen, Z., Marquis, M., Averyt, K.B.,, Miller, H.L. (Eds.), Climate Change 2007: The Physical Science Basis.on of Working Group I to the Fourth Assessment Report of the Inter-ntal Panel on Climate Change. Cambridge University Press, Cambridge,gdom/New York, NY, USA., A.J., 2009. Comments on no-tillage and soil-prole carbon seques-

on-farm assessment. Soil Science Society of America Journal 73,

ounsevell, M.D.A., Smith, P., Verhagen, J., 2004. Carbon sequestrationcultural soils of Europe. Geoderma 122, 123.r, I., Richardson, S., Hickman, G., Chambers, B., 2005. Landspreadingtural land: nature and impact of paper wastes applied in England andnce Report SC030181/SR. Environment Agency, Bristol.ambers, B.J., Chaudri, A.M., McGrath, S.P., Carlton-Smith, C.H., Bacon,bell, C.D., Aitken, M.N., 2006. Initial results from a long-term, multi-tudy of the effects on soil fertility and microbial activity of sludgeaining heavy metals. Soil Use and Management 22, 1121..J., Dailey, A.G., Williams, A.G., Evert, F.K., Goulding, v., Whitmore,, 2009. Is it possible to increase the sustainability of arable and rumi-ulture by reducing inputs? Agricultural System 99, 117125.., Waite, I.S., McNicol, J.W., Poulton, P.R., Macdonald, A.J., ODonnell,. Soil organic carbon contents in long-term experimental grasslande UK (Palace Leas and Park Grass) have not changed consistently inades. Global Change Biology 15, 17391754.riculture, forestry and other land use. In: Eggleston H.S., Buendia L.,gara T., Tanabe K. (Eds.), 2006 IPCC Guidelines for National Green-

Inventories, Prepared by the National Greenhouse Gas Inventoriese, vol. 4. IGES, Japan.., 1990. The turnover of organic-carbon and nitrogen in soil. Philosoph-ctions of the Royal Society of London Series B-Biological Sciences 329,

., Johnston, A.E., 1977. Soil Organic Matter in the Hooseld Continuouseriment. Rothamsted Experimental Station Report for 1976, Part 2, pp.

, 1975. The Woburn Market Garden Experiment, 19421969 II. Thethe Treatments on Soil pH, Soil Carbon, Nitrogen, Phosphorus and. Rothamsted Experimental Station Report for 1974, Part 2, pp.

Poulton, P.R., Coleman, K., 2009. Soil organic matter: its importance ine agriculture and carbon dioxide uxes. Advances in Agronomy, vol.ier Academic Press Inc., San Diego, pp. 157.li-Hall, M., Demetriades, A., Leifeld, J., Robert, M., 2004. Technicalroup on Organic Matter, Task Group 2 on Status and Distributionanic Matter in Europe, Final Report, May 2004. European Commissione General Environment, Multi-stakeholder Working Group Reports,atic Strategy.dley, R.I., Harrison, R., Carter, A.D., 2004. Carbon sequestration andtential associated with changes to the management of agriculturalgland. Soil Use and Management 20, 394402.

D.S. Powlson et al. / Agriculture, Ecosystems and Environment 146 (2012) 23 33 33

Kravchenko, A.N., Robertson, G.P., 2011. Whole-prole soil carbon stocks: the dangerof assuming too much from analyses of too little. Soil Science Society of AmericaJournal 75, 235240.

Lemke, R.L., VandenBygaart, A.J., Campbell, C.A., Lafond, G.P., Grant, B., 2010. Cropresidue removal and fertilizer N: effects on soil organic carbon in a long-termcrop rotation experiment on a Udic Boroll. Agriculture Ecosystems and Environ-ment 135, 4251.

Luo, Z.K., Wang, E.L., Sun, O.J., 2010. Can no-tillage stimulate carbon sequestra-tion in agricultural soils? A meta-analysis of paired experiments. AgricultureEcosystems and Environment 139, 224231.

Machado, P., Sohi, S.P., Gaunt, J.L., 2003. Effect of no-tillage on turnover of organicmatter in a Rhodic Ferralsol. Soil Use and Management 19, 250256.

Mattingly, G.E.G., Chater, M., Johnston, A.E., 1975. Experiments made on StackyardField, Woburn, 18761974 III. Effects of NPK Fertilisers and Farmyard Manureon Soil Carbon, Nitrogen and Organic Phosphorus. Rothamsted ExperimentalStation Report for 1974, Part 2, pp. 6178.

Nicholson, F.A., Chambers, B.J., Mills, A.R., Strachan, P.J., 1997. Effects of repeatedstraw incorporation on crop fertilizer nitrogen requirements, soil mineral nitro-gen and nitrate leaching losses. Soil Use and Management 13, 136142.

Oorts, K., Laurent, F., Mary, B., Thiebeau, P., Labreuche, J., Nicolardot, B., 2007. Exper-imental and simulated soil mineral N dynamics for long-term tillage systems innorthern France. Soil and Tillage Research 94, 441456.

Parton, W.J., ScKirchner, T1993. Obsefor the gra

Paustian, K., ANoordwijkemissions.

Poirier, V., AngJ., 2009. Inproles. So

Powlson, D.S.,for soil prAgronomy

Powlson, D.S., A.P., Hirsctainable ag

Powlson, D.S.,adenosinedirect-dril

Powlson, D.S., mitigate cfalse. Euro

Regina, K., Alaconvention

Rochette, P., 2and Tillage

Ros, M., Klammcompost aactivity. So

Royal Society,Change Ro

S.I., 2008. The 2008/2349

Sey, B.K., Whaand nitrouof America

Smith, P., Andmael, B., 2overestim

Smith, P., MarOMara, F.G., Roman2008. Greethe Royal S

Smith, P., Powsequestratresults fro

Smith, P., Powlson, D.S., Glendining, M.J., Smith, J.U., 1998. Preliminary estimates ofthe potential for carbon mitigation in European soils through no-till farming.Global Change Biology 4, 679685.

Smith, P., Powlson, D.S., Smith, J.U., Falloon, P., Coleman, K., 2000. Meeting Europesclimate change commitments: quantitative estimates of the potential for carbonmitigation by agriculture. Global Change Biology 6, 525539.

Smith, P., Smith, T.J.F., 2000. Transport carbon costs do not negate thebenets of agricultural carbon mitigation options. Ecology Letters 3,379381.

Snyder, V.A., Vazquez, M.A., 2005. Structure. In: Hillell, D., Hateld, J.L., Powlson,D.S., Rozenweig, C., Scow, K.M., Singer, M.J., Sparks, D.L. (Eds.), Encyclopedia ofSoils in the Environment, vol. 4. Elsevier, Oxford, UK, pp. 5468.

Stern, N., 2006. Stern Review Report on the Economics of Climate Change. www.hm-treasury.gov.uk/sternreview index.htm (9 September 2011).

Syswerda, S.P., Corbin, A.T., Mokma, D.L., Kravchenko, A.N., Robertson, G.P., 2011.Agricultural management and soil carbon storage in surface vs deep layers. SoilScience Society of America Journal 75, 92101.

Tian, G., Granato, T.C., Cox, A.E., Pietz, R.I., Carlson, C.R., Abedin, Z., 2009. Soil car-bon sequestration resulting from long-term application of biosolids for landreclamation. Journal of Environmental Quality 38, 6174.

Tomlinson, T.E., 1974. Soil structural aspects of direct drilling. In: Proceedings of the10th International Soil Science Congress, Moscow, ISSS, Moscow, pp. 203213.

nal Echesis .A.N., -termge ResenigenC stog eldronmygaar

ers, Dact of

agro234.ygaar

., Drurong-tence 90a, R.T.,re grence SoA.J.A., n me

age an. JournA.J.A.

ors aose- a199., P., 20and T, P., 2tscap.W., C, organsuredagemO., Pos

rotat194re, A.Pzation247.s, J.R.,n stracy, B.,re. Thurlock, J.M.O., Ojima, D.S., Gilmanov, T.G., Scholes, R.J., Schimel, D.S.,., Menaut, J.C., Seastedt, T., Moya, E.G., Kamnalrut, A., Kinyamario, J.I.,rvations and modeling of biomass and soil organic-matter dynamicsssland biome worldwide. Global Biogeochemical Cycles 7, 785809.ndren, O., Janzen, H.H., Lal, R., Smith, P., Tian, G., Tiessen, H., Van, M., Woomer, P.L., 1997. Agricultural soils as a sink to mitigate CO2

Soil Use and Management 13, 230244.ers, D.A., Rochette, P., Chantigny, M.H., Ziadi, N., Tremblay, G., Fortin,teractive effects of tillage and mineral fertilization on soil carbonil Science Society of America Journal 73, 255261.

Glendining, M.J., Coleman, K., Whitmore, A.P., 2011a. Implicationsoperties of removing cereal straw: results from long-term studies.

Journal 103, 279287.Gregory, P.J., Whalley, W.R., Quinton, J.N., Hopkins, D.W., Whitmore,h, P.R., Goulding, K.W.T., 2011b. Soil management in relation to sus-riculture and ecosystem services. Food Policy 36, S72S87.

Jenkinson, D.S., 1981. A comparison of the organic-matter, biomass,-triphosphate and mineralizable nitrogen contents of ploughed andled soils. Journal of Agricultural Science 97, 713721.Whitmore, A.P., Goulding, K.W.T., 2011c. Soil carbon sequestration tolimate change: a critical re-examination to identify the true and thepean Journal of Soil Science 62, 4255.kukku, L., 2010. Greenhouse gas uxes in varying soils types underal and no-tillage practices. Soil and Tillage Research 109, 144152.

008. No-till only increases N2O emissions in poorly aerated soils. Soil Research 101, 97100.er, S., Knapp, B., Aichberger, K., Insam, H., 2006. Long-term effects of

mendment of soil on functional and structural diversity and microbialil Use and Management 22, 209218.

2001. The Role of Land Carbon Sinks in Mitigating Global Climateyal Society policy Document 10/01. Royal Society, London.Nitrate Pollution Prevention Regulations 2008. Statutory Instrument.len, J.K., Gregorich, E.G., Rochette, P., Cue, R.I., 2008. Carbon dioxides oxide content in soils under corn and soybean. Soil Science Society

Journal 72, 931938.ren, O., Karlsson, T., Perala, P., Regina, K., Rounsevell, M., van Wese-005. Carbon sequestration potential in European croplands has beenated. Global Change Biology 11, 21532163.tino, D., Cai, Z., Gwary, D., Janzen, H., Kumar, P., McCarl, B., Ogle, S.,, Rice, C., Scholes, B., Sirotenko, O., Howden, M., McAllister, T., Pan,enkov, V., Schneider, U., Towprayoon, S., Wattenbach, M., Smith, J.,nhouse gas mitigation in agriculture. Philosophical Transactions ofociety B: Biological Sciences 363, 789813.lson, D.S., Glendining, M.J., Smith, J.U., 1997. Potential for carbonion in European soils: preliminary estimates for ve scenarios usingm long-term experiments. Global Change Biology 3, 6779.

UK NatioSynt

Ussiri, DlongTilla

van GroSoil usinEnvi

VandenBAngImpterm226

VandenBM.Ron lScie

Ventereage aScie

Vinten, vatiostorleys

Vinten, Factgluc190

WallaceLTD

WallaceGran

Watts, CclaymeaMan

West, T.crop1930

Whitmoerali237

WilliamcatioDArFutuosystem Assessment, 2011. The UK National Ecosystem Assessment:of the Key Findings. UNEP-WCMC, Cambridge.Lal, R., Jarecki, M.K., 2009. Nitrous oxide and methane emissions from

tillage under a continuous corn cropping system in Ohio. Soil andearch 104, 247255., K.J., Hastings, A., Forristal, D., Roth, B., Jones, M., Smith, P., 2011.

rage as affected by tillage and straw management: an assessment measurements and model predictions. Agriculture Ecosystems andent 140, 218225.t, A.J., Bremer, E., McConkey, B.G., Ellert, B.H., Janzen, H.H.,.A., Carter, M.R., Drury, C.F., Lafond, G.P., McKenzie, R.H., 2011.

sampling depth on differences in soil carbon stocks in long-ecosystem experiments. Soil Science Society of America Journal 75,

t, A.J., Bremer, E., McConkey, B.G., Janzen, H.H., Angers, D.A., Carter,y, C.F., Lafond, G.P., McKenzie, R.H., 2010. Soil organic carbon stocksrm agroecosystem experiments in Canada. Canadian Journal of Soil, 543550.

Baker, J.M., Dolan, M.S., Spokas, K.A., 2006. Carbon and nitrogen stor-ater under biennial tillage in a Minnesota cornsoybean rotation. Soilciety of America Journal 70, 17521762.Ball, B.C., OSullivan, M.F., Henshall, J.K., 2002a. The effects of culti-thod, fertilizer input and previous sward-type on organic C and Nd gaseous losses under spring and-winter barley following long-termal of Agricultural Science 139, 231243., Whitmore, A.P., Bloem, J., Howard, R., Wright, F., 2002b.ffecting N immobilisation/mineralisation kinetics for cellulose-,nd straw-amended sandy soils. Biology and Fertility of Soils 36,

05. Compost Use in Agriculture Consolidated Report. EB Nationwidehe British Potato Council.007. Compost use in agriculture consolidated report phase 2.e and the Applied Research Forum.lark, L.J., Poulton, P.R., Powlson, D.S., Whitmore, A.P., 2006. The role ofic carbon and long-term management on mouldboard plough draught

on the Broadbalk wheat experiment at Rothamsted. Soil Use andent 22, 334341.t, W.M., 2002. Soil organic carbon sequestration rates by tillage andion: a global data analysis. Soil Science Society of America Journal 66,6.., Groot, J.J.R., 1997. The decomposition of sugar beet residues: min-

versus immobilization in contrasting soil types. Plant and Soil 192,

Chambers, B.J., Smith, K.A., Ellis, S., 2000. Farm manure land appli-tegies to conserve nitrogen within farming systems. In: Petchey, T.,

Frost, A. (Eds.), Agriculture and Waste Management for a Sustainablee Scottish Agricultural College, pp. 167179.

The potential to increase soil carbon stocks through reduced tillage or organic material additions in England and Wales: A...1 Introduction2 Reduced tillage2.1 Definitions and current practice in the UK2.2 Generic issues regarding reduced tillage effects on soil organic carbon content2.3 Analysis of evidence on reduced and zero tillage impacts on soil organic carbon using data from UK2.4 Influence of reduced/zero tillage on nitrous oxide (N2O) emissions from soil

3 Organic material additions3.1 Generic issues on organic material additions.3.2 Analysis of evidence on impacts or organic material additions on soil organic carbon using data from UK3.2.1 Farm manures3.2.2 Biosolids3.2.3 Green compost3.2.4 Paper crumble3.2.5 Cereal straw

4 Discussion4.1 General issues regarding management impacts on soil organic carbon content4.2 Impacts of reduced/zero tillage on SOC and overall greenhouse gas emissions4.3 Impacts of organic material additions on SOC and overall greenhouse gas emissions

5 ConclusionsAcknowledgementsReferences