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The implications of phasing out conventional nutrient supply
in organic agriculture: Denmark as a case
Myles Oelofse & Lars Stoumann Jensen & Jakob Magid
Received: 6 October 2011 / Accepted: 20 May 2013 / Published online: 4 June 2013
#
Springer Science+Business Media Dordrecht 2013
Abstract Soil fertility management in organic sys-
tems, regulated by the organic standards, should seek
to build healthy, fertile soils and reduce reliance on
external inputs. The use of nutrients from conventional
sources, such as animal manures from conventional
farms, is currently permitted, with restrictions, in the
organic regulations. How ever, the reliance of organic
agriculture on the conventional system is considered
problematic. In light of this, the organic sector in
Denmark has recently decided to gradually phase
out, and ultimately ban, the use of conventional ma-
nures and stra ws in organic agriculture in Denmark.
Core focal areas for phasing out conventional nutrients
are as follows: (1) amendments to crop selection and
rotations, (2) alternative nutrient sources (organic
wastes) and (3) increased cooperation between organic
livestock and arable farmers. Using Denmark as a
case, this article discusses the background and impli-
cations of the strategy to phase out conventional ma-
nure and straw, and explores possible solutions to the
challenge of ensuring a sustainable nutrient supply to
organic systems. Alternative strategies to ensure nutri-
ent supply will require a tapestry of small solutions.
One element of this tapestry is to review the volume
and type of nutrient sources available in alternative,
non-farm organic waste streams and consider their
suitability for use in organic systems.
Keywords Organic agriculture
.
Soil fertility
management
.
Organic fertilisers
.
Nutrient
management
.
Organic waste
Introduction
Soil fertility management in organic farming systems,
seeking to build healthy soils, can occur through crop
rotation design, crop residue management and the appli-
cation of animal manures, composts and a variety of
permitted fertilisers and soil conditioners (European
Communities 2007; I FOAM 2005). Organic farms
should, where possible, be self-sufficient in nutrients by
producing and reusing materials on-farm (Davis and
Abbott 2006) and farmers’ nutrient management strate-
gies should focus upon efficient use of organic materials
and land management practices (von Fragstein und
Niemsdorff and Kristiansen 2006). Organic regulations
permit the use of approved fertilisers and soil condi-
tioners (European Communities 2007). However, import
of nutrients should not form the core fertility manage-
ment strategy on organic farms and should only supple-
ment nutrient supply under circumstances where the
farmer has no other option (IFOAM 2005).
Although organic agriculture seeks to decrease re-
liance on external nutrients sources, organic farmers in
different contexts still rely upon the import of nutrients
from conventional agriculture to varying degrees, see
for example Kirchmann et al. (2007). Current organic
regulations for countries of the European Union
(Council Regulation (EC) No 834/2007) permit the use
of 170 kg N ha
−1
from animal manure. Although farmers
Org. Agr. (2013) 3:41–55
DOI 10.1007/s13165-013-0045-z
M. Oelofse (*)
:
L. S. Jensen
:
J. Magid
Department of Plant and Environmental Sciences,
Faculty of Science, University of Copenhagen,
Thorvaldsensvej 40,
1871 Frederiksberg, Denmark
e-mail: myles@life.ku.dk
must pr ovide documentation for the need to use
manure from a conventional source, its use is still per-
mitted (European Communities 2007). For example, in
Denmark, where the EU regulations are a minimum
requirement, the rules state that a maximum of 70 kg
Nha
−1
can be sourced from conventional manure with-
out justification, whilst the Soil Association in the UK
allows the use of non-organic manure, yet require justi-
fication and documentation of sourcing (Soil Association
2010; Plantedirektoratet 2010).
The uptake and spread of organic agriculture is a
transitional and dynamic process. This process encom-
passes working out how best to move towards the goal
of a more ideal organic agriculture, embodied in the
organic principles. The goal of an ideal organic agri-
culture entails seeking agricultural systems with min-
imal negative effects on the environmen t, animals and
society in general, and can be seen as something as an
ultimate goal, which organic agriculture seeks to move
toward. An example of the dynamic nature of organic
agriculture is the decision to disallow the use of con-
ventional feed in organic systems. Similarly, the or-
ganic sector in Denmark is aware that reliance on
nutrients produced in a manner not aligning with the
organic princ iples is not acceptable in the long term.
Organic agriculture in Denmark should ideally be
sustainable and operate independently of the conven-
tional food system (Kyed et al. 2006).
In recognition of this conflict between principle and
practice, the two main organic agricultural organisations
in Denmark have decided to gradually phase out, and
ultimately ban, the use of conventional straw and ma-
nure in organic production. The decision was made in
order to improve internal and regional nutrient recycling
on organic farms and decrease organic agricultures’
reliance upon conventional agriculture. The decision
was also made to prevent the import of genetically
modified organisms (GMOs) into organic systems via
manure from animals fed with feeds from genetically
modified crops. It raises a number of challenges for the
organic sector in Denmark, particularly since many
organic farmers’ nutrient management strategies are
based upon the current rules, which allow a broad range
of inputs which in the future will be banned (Jørgensen
and Kristensen 2010).
The decision to eliminate the use of convent ional
manures and straw in organic systems in Denmark
means that organic farmers will need to rethink both
farming system design (crop rotation, tillage systems,
livestock integration) as well as sourcing of nutrients
in future strategies. The aim of this paper is to discuss
and explore the implications of banning the use of
conventional animal manure in organic systems, using
Denmark as a case. We will focus upon nutrient
recycling in arable systems and review what types of
technological options are currently applied and might
be available in the future for organic farming systems.
The pap er will particularly focus upon the role that the
recycling of different types of organic waste products
can play as a nutrient source in organic systems.
Methodology
The analysis is based upon a review of peer-reviewed
literature and literature specifically related to the
Danish context. Using Denmark as a case, we start
by giving a background to the decision to phase out
manures and straw and the solutions already set for-
ward within the Danish organic sector. The core focal
areas for phasing out conventional nutrients are as
follows (1) amendments to crop selection and rota-
tions, particularly the role of catch crops in the rotation
and improving nutrient use efficiency; (2) alternative
nutrient sources (organic waste), including the role of
biogas and (3) increased cooperation between organic
livestock and arable farmers. The focus of our review
is on the potential role of alternative nutrient sources.
The review thus focuses upon plant production sys-
tems, and therefore on the effects of banning conven-
tional animal manure, as the impact of banning con-
ventional straw will primarily affect animal producers
(and some specialist vegetable producers such as car-
rot). Following the presentation of the Danish case, we
broaden the review to explore the general literature to
discuss the advantages and disadvantages of alterna-
tive nutrient sources.
The case of Denmark
Background and proposed strategy
The strategy for phasing out conventional manure and
straw is the result of a process started almost 10 years
ago. Organic Denmark (OD) and the organic section at
the Danish Agriculture and Food Council (DAFC)
sought to make a decision in 2003 to be implemented
42 Org. Agr. (2013) 3:41–55
by 2011. However, given the extensive consequences
of such a decision, the decision was delayed until
further research had been conducted to investigate
the imp lications of a ban and possible solutions ex-
plored. An extensive analysis was thus prepared by
Kyed et al. (2006) to, firstly, report the extent of use of
conventional manures and straw in Danish organic
agriculture and, secondly, conduct economic calcula-
tions based upon scenarios for different producer types
in order to estimate the economic consequences.
Following further investigation into the consequences
of a ban, the proposal to phase out conventional ani-
mal manures and straws in organic agriculture was
passed at Organic Denmark’s annual general meeting
in 2008. The decision thus emanates from the organic
farmers themselves and still needs to be linked legis-
latively with the current rules in Denmark. The pro-
posed strategy, passed in 2008, was originally
intended to start in 2015. It was decided that for
manure sources,
1
in line with current regulations, or-
ganic farmers are allowed to import 70 kg N ha
−1
from
conventional sources until 2015. In 2015, the amount
will be reduced annually by 10 kg N ha
−1
, and by
2021, the permitted amoun t of conventional manures
will be zero. In early 2012, the boards of OD and
DAFC agreed to an amendment of the 2008 proposal.
The new plan has removed the requirement of annual
reductions of 10 kg N ha
−1
from 2015 until 2021 but
retains the 2022 target of a complete ban on conven-
tional manure use in organic agriculture.
2
The amend-
ment was made in order to give more time to find new
solutions, and in recognition of the fact that the 2015
deadline has caused significant uncertainty among
organic farmers as well as farmers considering con-
version. The two organisations, furthermore, recognise
that there need to be concrete solutions available for
farmers before starting such a ban. It is expected that
as more alternative nutrient sources become available,
or improved methods developed, the amount of N
permitted from conventional sources will be reduced.
As such, it is expected that the amount of permitted N
will be reduced to 50 kg ha
−1
in 2017.
Possible consequences
The main organic production system types in
Denmark are dairy, arable and horticultural systems.
Geographically, organic farming in Denmark is
characterised by a marked regional distribution pattern
of farm types (Frederiksen and Langer 20 04). The
geographical spread of organic farms emanates from
specialisation trends in the general farming sector.
Animal production is mostly concentrated in West
Denmark (Jutland), whil st most plant production is
located on the islands of Eastern Denmark. This geo-
graphical divide will, in particula r, have connotations
for (1) the supply and trade of organic manure and
straw in the future, and (2) how the organic sector is
expected to develop and expand with the new rules,
given that land ownership requirements for conven-
tional animal producers, which stipulate that animal
producers must have an area corresponding to the
number of animals, is expected to drive land prices
up in livestock-rich areas.
Kyed et al. (2006) presented a number of scenarios
with calculations of the potential economic conse-
quences of the ban for organic crop and vegetable
producers. The ban will invoke responses other than
a simple input substitution (purchasing of organic
manures), as explored below. The results of the eco-
nomic scenarios are strongly influenced by organic
farm location: the price of imported manure was cal-
culated to increase from 2.8 to 5.2 Euro per ton ma-
nure for farms located in areas where organic animal
production is concentrated, whilst the price was cal-
culated to increase from 4.2 to 12.1 Euro per ton
manure in areas with a low concentration of organic
animal farms. Predictions of this nature have a high
uncertainty, although they provide an idea of the ex-
tent of possible increased production costs for farmers.
Tvedegaard (2007) conducted ten case studies of
different types of organic farms in order to elucidate
the type of case-based consequences. Scenarios for the
three arable farmers studied generally entailed a large
reduction in the amount of manure applied and
changes t o their rotation involving an increase in
nitrogen (N)-fixing plants and a reduction in grain
production, resulting in considerable additional costs
for farmers. Likewise, the case studies of specialist
1
For straw, from 2015, organic farmers will be required to
document that: (1) straw used has not been sprayed with pesti-
cide up to 1 month before harvest and (2) that no crop growth
regulator has been applied. From 2021, the use of non-organic
straw can only occur if approved by the authorities.
2
For straw, the legislative requirements of proving the origin of
straw require further investigation by The Danish AgriFish
Agency. However, the new strategy stresses the desire to work
towards a reduction in use of non-organic straw in organic
agriculture.
Org. Agr. (2013) 3:41–55 43
vegetable producers showed increased economic cost
and the risk of either discontinuing production or
having to move farms closer to an organic animal
farm. Paradoxically, for one farmer, the ban would also
entail an increased import of organic fertiliser (which he
sources from Holland) and organic straw (from approx-
imately 80 km away).
Kyed et al. (2006) presen t a range of possible re-
sponses by organic crop producers, the most notewor-
thy of which include strategies to increase the amount
of fertility building crops in the rotation, the importing
of organic livestock manure (up to 40 km away),
reverting to conventional farming or including an an-
imal production component on the farm (integrated
production). A particularly startling potential scenario
is that there is a risk that a large number of organic
crop produce rs in areas with a low concentration of
organic livestock will either stop farming or revert to
conventional farming (Kyed et al. 2006).
Tvedegaard’s(2007) conclusions from the farm
case studies succinctly outline the potential challenges
ahead. The ban will mean that a contentious issue
(reliance on conventional agriculture) in organic agri-
culture will be resolved, but it will also cost organic
farmers money, lead to fewer organic farmers, result in
increased imports of organic products, increase trans-
port and not improve animal welfare (due to chal-
lenges in supply of organic material for bedding).
The decision puts Denmark at the forefront of the
international organic sector and, taking an optimistic
outlook, the decision will enhance the reputability and
consumer credibility of organic agriculture and secure
a future sustainable development of the sector.
However, from a critical standpoint, the initiative
might undermine the foundation of the Danish organic
farming sector, putting an expansion of organic farm-
ing in Denmark at risk. The recognition of this risk is
already evident in the recent amendment of the strat-
egy. In particular, organic farmers in the rest of the EU
might have a comparative advantage over Danish
farmers in that they will not be restricted in their use
of conventional manures and stra w. Furthermore, con-
cern has been raised whether the ban might lead to
increased nutrient mining due to lower inputs as well
as the fact that organic farmers in the future are likely
to increasingly transport organic inputs from further
away, causing higher energy use in organic produc-
tion. However, in the long term, a decision of this
nature will move the organic sector closer to realising
the goal of being independent of the conventional
system.
Looking forward: strategies to meet the challenge
in Denmark
There are a number of important institutional initiatives
which have been implemented in the past few years
which are of great strategic importance for the organic
sector. In 2009, the Danish government announced their
vision for 2020, entitled Green Growth. The plan con-
tains an ambitious goal of doubling the organic area in
Denmark by 2020 which will mean organic land will
make up 15 % of the total farmed area (Ministry
of Economic and Business Affairs Denma rk 2009;
Dalgaard et al. 2009). In conjunction with this, the gov-
ernment plans to increase biogas production significantly,
not only in order to decrease reliance on fossil energy
sources but also to increase energy recovery and
recycling of animal manure, the goal being set at 50 %
of all manure to be processed in biogas plants by 2020.
Institutional support for such initiatives is imperative to
ensure the continued growth of the organic sector as well
as to ensure the regional supply of organic inputs. This
point will be elaborated upon in the biogas section below.
Central actors in the organic sector in Denmark
recognise that there is no single solution to meet the
future challenge of operating without conventional
nutrients—meeting the challenge will require a mosaic
of different strategies (Jørgensen and Kristensen 2010).
For example, studies such as Thorup-Kristensen et al.
(2012) can be central to finding applicable solutions.
The Danish organic agriculture advisory services will
play a pivotal role during the phasing out process and
considerable attention has been given in the past few
years and will be in the forthcoming years, to ensure
farmers are fully prepared. The overall strategy outlined
by a working group commissioned by OD and DAFC
identifies an array of programme areas which should be
considered in unison (Jørgensen and Kristensen 2010).
Central elements of the strategy include:
& Crop rotation design: even more important than
before the ban, particularly enhancing understand-
ing of nutrient supply and release at different
stages in the rotation
& Increased and improved nutrient recycling: in the
field, from animal houses to field, and at a regional
scale from urban to rural areas
44 Org. Agr. (2013) 3:41–55
& Green manures and catch crops: increased knowl-
edge building and dissemination of their role, par-
ticularly optimization of timing of nutrient release
& Biogas: develop biogas plants that can run on plant-
based feedstock. Particularly in East Denmark,
where the lack of organic animal production means
farmers will lack manure
& Yields: increased focus on factors other than
fertilisers effect on yields, such as climatic factors,
crop rotations and crop health
& Breeding and use of crop cultivars which are more
appropriate for low-nutrient conditions
& Increased cooperation between organic livestock
and arable farmers (Jørgensen and Kristensen
2010)
Nitrogen supply is not the largest chall enge in
arable organic systems in Denmark as its supply can
be biologically contr olled in the system (Thorup-
Kristensen et al. 2003). The challenge with nitrogen
is to reduce losses from the system whilst ensuring a
sufficient suppl y. Supplying nutrients which cannot be
reintroduced biologically such as potassium (K) and
phosphorous (P) will be an increasing future challenge
for organic farmers. Phosphorous is very insoluble and
immobile in the soil; therefore, even if the soil con-
tains considerable amounts, availability is typically
low for many plant species. The challenge with phos-
phorous and other immobile nutrients is thus not just
one of supply but also improving plant accessibility.
Measures to improve the bioavailability of phospho-
rous centre upon improving the crops’ ability to access
immobile nutrients, for example crops with root sys-
tems developed for low-nutrient conditions, and en-
suring that soils have high biological activity (Brady
and Weil 1999). Potassium supply in soils is mainly
influenced by soil mineralogy, an inherent property
which is difficult to amend. Amendments to improve
potassium-depleted soils will thus have to be based
upon external inputs, either in permitted mineral forms
or in organic inputs such as animal manure. Micro-
nutrient supply in organic systems can primarily be
improved by ensuring a continued supply of organic
matter to soils coupled with increased biological activity
(Stockdale et al. 2002).
Securing a sufficient supply of nutrients will play a
pivotal role in securing cropping system sustainability.
In the next section, we explore the various types of
nutrient sources, which either currently are or might be
available to organic farmers in the future, and discuss
the feasibility as well as the pros and cons of their use.
Organic fertilisers and amendments
Fertilisers permitted in organic agriculture can be broad-
ly categorised into two groups: organic materials and
naturally occurring ge ological resources (Davis and
Abbott 2006). Figure 1 presents an overview of sources
of organic materials which currently are or might, in
future, be used in organic systems. Before application to
arable land, organic regulations demand that most
sources presented in Fig. 1 be subject to pretreatment,
typically through a composting process or a bio gas
digester. This may not always be ideal from a nutrient
efficiency viewpoint, as losses are almost inevitable;
however, it is often req uired for sanita ry reasons.
Some of the sources are currently permitted in organic
regulations, for example animal manure, whilst other
sources are currently not permitted (e.g. sewage sludge)
or permitted with restrictions (e.g. household food
waste). With justification and documentation of con-
tents, a variety of naturally occurring minerals are cur-
rently also permitted in organic systems, for example
rock phosphate, natural rock potash, lime and elemental
sulphur (European Communities 2007; Davis and
Abbott 2006). Restrictions in agronomic use of treated
organic waste and naturally occurring mineral resources
typically arise due to potential risk of contamination
from heavy metals, pathogens, salts and weed seeds
(Hargreaves et a l. 2008 ; Quilty and Cat tle 2011).
Organic fertilisers permitted for use in organic farming,
and the restrictions which might apply, are stipulated in
the specific requirements of organic certifiers (e.g.
European Union regulation).
Products labelled as organic fertilisers or organic
amendments in various forms are increasingly being
produced by manufacturers for commercial purposes.
Following treatment, organic wastes can be processed
to varying degrees for use in agriculture. End products
can range from a bulky product such as slurry to
products such as chicken manure pellets marketed as
organic fertiliser. For example, Quilty and Cattle
(2011) demonstrate in thei r categorisation of organic
fertiliser products available on the Australian market
that there is a very large supply of different product
types developed from a broad variety of feedstocks
(see Table 2, Quilty and Cattle (2011)) .
Org. Agr. (2013) 3:41–55 45
Organic waste products can effectively be treated
either by composting or anaerobic digestion (Odlare et
al. 2011). Composting of organic matter is a biological-
ly mediated and oxidative process which results in the
formation of humified organic material (Hargreaves et
al. 2008). The mineral composition of composted or-
ganic matter depends upon the type of feedstock used;
however, composted organic matter is generally consid-
ered a sufficient source of plant nutrients and organic
matter (Evanylo et al. 2008; Bulluck et al. 2002).
Anaerobic digestion of organic wastes leads to the pro-
duction of biogas (methane and carbon dioxide) and a
residual product, which can be used as an organic
amendment (Arthurson 2009).
In the following sections, we will present and dis-
cuss different potential uses of organic amendments,
focussing upon: (1) the amount and technical feasibil-
ity of their use in organic agriculture from the Danish
case perspective, (2) the efficacy of the product from a
plant production perspective and (3) use of the amend-
ment in organic agriculture regarding technological
feasibility and legislation.
Animal manures and slurry
The merit of using animal manures, in different forms,
as a fertiliser is a well-researched topic (Diacono and
Montemurro 2010; Edmeades 2003). Animal ma-
nures
3
are the most readily available organic nutrient
inputs for organic farmers in Denmark. Howeve r, the
question is whether organic systems in Denmark can
be self-sufficient in organically produced manures and
slurries? The most recent analysis of Danish organic
farmers’ production and use of manure and slurry was
conducted by Kyed et al. (2006) and presented in Table 1.
Their analysis is based on Danish fertilisation/manure
accounting statistics from 2002 and uses the organic area
in Denmark as registered in the General Agriculture
Registry in Denmark. Manure amounts are registered in
kilogram of total nitrogen per hectare. We used weighted
ratios of N to P and K standard values for nutrient
contents from the Danish manure registry (Ministry of
Food Agriculture and Fisheries 2008) in order to calcu-
late applied amounts of phosphorous and potassium.
4
The amount of imported non-organic manure was
on average 24 kg N ha
−1
. Organic arable farms supply
of organic manure consists of organic manure either
from the farms own livestock or through imports from
other organic farms. Not eworthy is the difference in
amount of manure applied by arable and dairy farmers.
Organic dairy farmers, with their own supply of ma-
nure, applied on average 51 kg N ha
−1
more than
arable farmers. Dairy farmers were found to sell or-
ganic manure to other organic farmers, although they
still imported non-organic manure. It is important to
note that the per hectare reliance upon imported non-
organic manure presented in Table 1 is most likely
much higher when considering actual manure use on
organic farms. The aggregated amount of non-organic
manure presented in Table 1 is calculated based on all
organic land, thus including areas receiving no or very
little manure (such as all organic land planted to ni-
trogen fixing crops). As such, it is estimated that for
3
Animal manure includes faeces and urine excreted by the
animal as well as bedding material and spilt feed depending
on the different production systems
4
According to Kyed et al. (2006), conventional pig slurry is the
primary type of imported manure to organic farms. The propor-
tion (DK total) of applied manures in 2002 was as follows: deep
bedding, 26 %; cattle slurry, 39 %; pig slurry, 17 %; other liquid,
14 %; and other, 4 %.
Industrial
waste
Animal
manure
Household
food waste
Toilet
waste
Green
wastes
Crops
Animals
Food/other
industries
Humans
Arable
land
Fig. 1 Options for nutrient
recycling from different or-
ganic waste sources. Wastes
are treated before land ap-
plication by processes such
as composting or biogas.
Figure adapted from
Kirchmann et al. (2005)
46 Org. Agr. (2013) 3:41–55
land receiving manure, the amount of non-organic
manure actually applied is most likely to be considerably
higher (Personal communication, Mejnertsen (2011)).
Table 2 presents the latest figures (2008) for produc-
tion of animal manure, from conventional and organic
farms, in Denmark. Whilst the values presented in
Table 2 are for volumes, they provide an indication of
the amount of organically derived manure available. For
example, a hypothetical application of all organically
derived manure to all organic land, from Table 2,would
supply 10.8 tons/ha. Using a nitrogen content of 0.5 %
would give a supply of 54 kg/ha. Comparing this to the
average of 88 kg N ha
−1
from Table 1,eventhoughthese
numbers are derived from different years, provides an
indication that there might be a shortfall in supply.
Livestock, and hence manure, production is concentrat-
ed in western Denmark. Although the theoretical short-
fall of organic manure supply may not be very large, the
problem for organic farmers will be one of distribution.
Organic crop and vegetable farmers located in an eco-
nomically feasible radius (for transportation) of organic
livestock producers will, to a certain extent, be able to
trade bedding material for organic manure, whilst trans-
port and other costs will determine how much other
farmers will import.
Residues from biogas production
Biogas and residue production through anaerobic diges-
tion of organic wastes from agriculture and other sources
has a potential for increased regional energy production
and nutrient cycling (Arthurson 2009). Biogas produc-
tion is identified as a priority area in the Danish govern-
ments’ Green Growth Plan (Ministry of Economic and
Business Affairs Denmark 2009). The strategy involves
providing financial support for the establishment of
localised biogas production plants. The Danish govern-
ment is interested in the production of energy with the
co-benefit of reducing the environmental threat posed by
the large amount of manure produced in Denmark by
utilising animal manure as a feedstock. The vision thus
entails locating biogas plants strategically to ensure that
local benefits are accrued. Organic organisations in
Denmark are generally optimisti c about the contri-
bution organic biogas plants can make to more sustain-
able energy production as well as a source of organic
fertilisers, and concerted efforts are underway to pursue
the development of organic biogas plants across the
country.
Organic standards permit the use of biogas residues
as a soil amendment, although with restrictions. Of
particular importance is that the feedstock must be
organically produced, for example the land application
of residue of digested conventionally produced clover
would not be permitted in organic systems. However,
source-segregated household waste is permitted as an
input in organic farming, although the waste should
either be composted or digested in a biogas plant.
Other feedstocks which, following digestion, provide
residues permitted in organic farming include organic ma-
nure, organic crops and residues, biomass from meadows,
organic butchery waste products (Tersbøl 2009).
In Denmark, there are approximately 80 biogas
plants: 20 of which are centralised plants and 60 are
farm-scale plants (Birkmose 2009). Typical feedstock
Table 1 Average amounts (in kilogram per hectare) animal manure applied in Denmark by organic farmers (for 2002), based on
analysis by Kyed et al. (2006)
Arable farms Dairy farms Total DK
NP KN PK NPK
Total applied 65 13 59 116 24 105 88 18 80
Amt of total from conventional sources 25 5 23 22 4 20 24 5 22
Sale of organic manure 0 0 0 14 3 13 0 0 0
Table 2 Annual production of animal manure (in 1,000 tons) in
Denmark by livestock and holding type (2008)
Conventional Organic Organic %
Pig 20,600 133 0.6
Cattle 15,486 1,660 9.7
Poultry 703 22 3.1
Other
a
1,295 51 3.9
Total 38,083 1,866 4.7
Source: Personal communication, Knowledge Centre for Agri-
culture 2011
a
Other includes fur animals, horses, sheep, deer and goats
Org. Agr. (2013) 3:41–55 47
for the centralised plants is a mixture of pig and cattle
slurry, deep litter and industrial organic waste prod-
ucts. Farm-scale plants are typically located on pig
farms and utilise pig slurry and organic waste
(Birkmose 2009). As such, the use of energy crops
as a feedstock for biogas plants is minimal as it is not
economically viable. A general challenge for the de-
velopment of biogas production in organic agriculture
in Denmark will be the sourcing of sufficient biomass
to ensure an optimal mix of feedstock. Manure and
slurry from conventional agriculture is produced in
abundance; however, the use of this in organic biogas
plants is not permitted. Since organically derived ma-
nure will be a contested resource in the future, feed-
stock for organic biogas plants will primarily be made
up of biomass from green manures, such as clover
grass, grown by organic farmers (Tersbøl 2008).
Running biogas plants on feedstock with a high percent-
age of dry matter, as is the case for green manures, is not
a standard procedure and will thus require technological
advances to ensure an optimal functioning of the plant
(Tersbøl 2008).
Amendments to organic farmers’ rotations that in-
crease the amount of green manures and reduce the
amount of cash crops will invariably have econ omic
implications for farmers, as will investment in new
biogas plants. The economic outcome for farmers will
depend upon a range of factors, particula rly whether
farmers have their own plant or a shared local plant.
5
Economic calculations based on scenarios are often
farm specific; therefore, the implications for farmers
will depend on a range of factors such as potential
earning from sale of energy production, sale of organic
fertilisers, sale of biomass, potential increase in subsi-
dies due to an increased proportion of green manures
in the rotation, either reduce d earnings from crop
production (lower percentage of cash crops in the
rotation) or increased earnings (higher yields following
the use of biogas slurry as a fertiliser), transport costs
depending on location of plant and future crop prices
(Tersbøl 2008, 2009;Fog2010).
The quality of biogas residue as a soil condition er is
influenced by the composition of feedstock used for
biogas production (Arthurson 2009). Arthurson (2009)
found that biogas residues typically contain high con-
centrations of mineralized N and low concentrations
of heavy metals and thus offer an alternative to min-
eral fertilisers. The experimental work reviewed
consisted of biogas effluents from various sources,
typically animal manures in different forms, domestic
household waste and municipal solid waste. Birkmose
(2007) compa red analyses of digested slurry (based on
a mixture of 50 % pig slurry, 25 % cattle slurry and
25 % organic industrial waste) with undigested cattle
and pig slurry, showing that the digested slurry had a
slightly lower dry matter content and a higher ammo-
nium nitrogen content. The content of P was similar,
whilst K content was similar for undigested pig slurry
and digested slurry, but higher for cattle slurry.
Organic biogas plants in Denmark are envisaged to
run primarily on biomass from organic farms; thus,
concern about contaminants should be minimal.
Ensuring a sufficient and timely nitrogen suppl y is
critical for securing sufficient yields. This can occur
through an increased proportion of nitrogen fixing
crops and cash crops; however, a major challenge in
organic systems is to match N supply with crop de-
mand whilst sim ultaneously minimising nutrient loss
(Pang and Letey 2000). Contrary to nitrogen that is
organically bound, N in ammonium form is readily
available for plant uptake; therefore, biogas slurry can
provide a viable option for crops where an early and
timely supply of nitrogen is important.
Recycling of non-farm organic waste
Central concerns related to the use of non-farm organ-
ic wastes as fertilisers in agriculture are particularly
about ecosystem and human health effects of contam-
inants and odour issues. Other issues are often of a
technological or economic nature, in particular wheth-
er there is a sufficient waste supply to warrant a cost-
effective investment in treatment technology and
transportation to farmers’ fields. In line with this, the
potential use of non-farm organic waste products in
agriculture also depends strongly upon farmers’ will-
ingness to use the products. Analysing Denmark’s
non-farm waste production exemplifies the potential
that organic waste might hold for organic agriculture
in the future. Denmark’s total non-farm waste produc-
tion in 2009 was 13.9 million tons (Danish Ministry of
the Environment 2011). Table 3 presents a breakdown
of the available amounts and the theoretical nutrient
supply potential of the organic fraction of different
types of non-farm waste in Denmark.
5
For specific scenarios, please see Fog (2010) and Tersbøl (2008).
48 Org. Agr. (2013) 3:41–55
The values in Table 3 provide a theoretical nutrient
supply potential, with the hectare distribution based
upon a total supply to curren t organic agriculture. It is
important to note that some of the potential nutrient
streams are already partially recycled in Denmark, e.g.
to private gardens, landscaping or conventional agricul-
ture. However, Table 3 still demonstrates that there is an
untapped nutrient potential from non-farm waste types.
In particular, there is a large potential in uncollected
household organic waste and garden and park waste
for nitrogen and potassium and in sewage sludge for
nitrogen and phosphorus.
Whilst an increase in recycling of animal wastes,
slurry and biogas residues (described in the above
sections) adheres to the notion of non-reliance on
conventional agriculture, we recognise that a large
proportion of nutrients recycled from non-farm organ-
ic wastes such as sew age sludge or household waste
will inevitably emanate from conventional agriculture.
It might therefore be considered paradoxical to recom-
mend their usage in organic agriculture. The question
is whether the recycling of non-farm organic wastes
actually represents a real reliance on conventional
nutrients (compared to reliance on conventional ani-
mal manure) or a sensible reuse of a product which
would most likely be incinerated? This is a discussion
of principles and is perhaps an issue which requires
discussion within organic agriculture about whether
this can be a considered breach of principles, a com-
promise or a fulfilment of the organic ideology of
working with closed cycles. In the following sections,
we will discuss issues related to the potential use of
non-farm waste types in organic agriculture.
Source-segregated organic waste
Current EU organic regulations permit the conditional
use of source-segregated household waste (European
Communities 2007). In Denmark, only a small per-
centage of the organic fraction of household domestic
waste is source separated and recycled (12 %). Source-
segregated household waste is either digested in a
biogas plant or composted. The large proportion of
non-segregated organic waste in Denmark, which is
currently incinerated for energy recovery in combined
heat and power plants, holds a future potential for
treatment and potential use in agriculture, as evident
in Table 3. However, in order for this to occur requires
a significant adaptation of current refuse collection
infrastructure, in particular for private households
Source-segregated organic waste as a soil amend-
ment has typically been investigated under the broad
term of municipal solid waste (MSW). Although there
is no common definition of MSW, the term generally
includes solid waste from households, busine sses and
institutions (Gerba et al. 2011), although Hargreaves et
al. (2008) refer to MSW as being largely made up of
kitchen and yard waste. Hence, a review of the prop-
erties of source-separated organic waste, or MSW,
should take heed of the type of composting or biogas
Table 3 Theoretical nutrient supply potential by non-farm organic waste type in Denmark
DM (t) N (t) P (t) K (t)
Household source-segregated organic waste
a
(currently recycled) 14,865 282 34 189
Household waste
a
, organic fraction
a
estimate (currently incinerated) 228,800 4,347 526 2,906
Garden and park waste (private and public) 409,635 2,222 394 3,892
Service sector organic waste
a
9,756 185 22 124
Industrial sector organic waste
a
35,495 53 9 93
Sewage sludge 132,600 6,312 4,150 716
Total (t) 831,151 13,402 5,137 7,919
Supply to organic agriculture
b
(kg/ha)
b
4,790 77 30 46
Sources: (1) waste quantities: Danish Ministry of the Environment 2011; Danish Ministry of the Environment 2009; Personal
communication, Petersen 2011; (2) nutrient contents: Boldrin 2009; Boldrin and Christensen 2010; Boldrin et al. 2011; Danish Ministry
of the Environment 2009
a
Based on the nutrient content of the vegetable food waste fraction of household waste
b
Based on a theoretical distribution of total nutrients from organic waste streams to all organic land in Denmark (173,517 ha)
Org. Agr. (2013) 3:41–55 49
feedstock used and the proportions, the treatment facil-
ity design, and the composting procedure and matura-
tion period (Hargreaves et al. 2008).
Hargreaves et al. (2008) conducted a comprehen-
sive review of the use of composted municipal solid
waste in agriculture. The authors revie w the effects of
composted MSW on soil physical, biological and
chemical properties. Whilst the review shows that
MSW compost has a potential as a beneficial recycling
tool, the authors stress that, due to the large variability
in compost content, MSW composts should be con-
sistently monitored. Monitoring should be conducted
using standardised procedures to determine bioavailabil-
ity of nutrients, metals and trace elements, and a measure
of the content of organic pollutants (Hargreaves et al.
2008). Farrell and Jones (2009) conclude in their review
that composts from MSW and mechanical biological
treatment residues are rich in plant-available nutrients,
although in some cases, the inorganic salt levels might be
too high.
6
They thus find that MSW composts potential
to improve soil quality make them ideal for agriculture,
although correct measures should be taken to mitigate
environmental damage and improve public acceptance.
Smith (2009a) reviewed studies concerning the bio-
availability of heavy metals in MSW composts and
sewage sludge. The review demonstrates that the total
heavy metal content of composted source-separated
MSW is lower than that of sewage sludge. How ever,
it is important to note that the phosphorous content of
sewage sludge is typically higher than that of
composted MSW; therefore, consideration should be
given to the ratio of P to heavy metals when using
these wastes as fertilisers. Furthermore, the heavy
metal concentrations of different types and sources of
organic waste, presented by Smith (2009a), demon-
strate that source-segregated waste had markedly low-
er concentrations than mechanically separated MSW, a
finding resonated in a review conducted by Farrell and
Jones (2009)
Comparing heavy metal concentrations reviewed
by Smith (2009a) with the limits set by the organic
regulations (for content of composted or digested
household waste) reveals that some green waste and
source-segregated wastes can fall below the current
thresholds, although this is not always the case for
all waste sources (Smith 2009a). Heav y metals will
accumulate slowly in soils following long-term
application of composts; however, the review found
little evidence of phytotoxic effects or accumulation of
heavy metal in crop tissue that may pose a threat to
human health from compost or compost-amended soil.
Smith (2009a) concludes that ‘risks to the envir on-
ment, human health, crop quality and yield, and soil
fertility, from heavy metals in source-segr egated
MSW or greenwaste-compost are minimal’ . Farrell
and Jones (2009) reviewed research of the content of
organic contaminants in composted MSW and con-
clude that, whilst composting provides a critical step
in treatment for organic contaminant removal, a clear
understanding of various aspects of how composting
affects organic contaminants is lacking.
Sewage sludge
In Denmark, sewage sludge (biosolids) is collected from
municipal and private wastewater treatment plants.
Approximately 800,000 tons of sludge (in wet weight)
was produced by wastewater treatment plants in 2008,
56 % of which was recycled to agricultural land
(conventional), 43 % incinerated (ashes typically
recycled into cement or road construction materials)
and 1 % landfilled (based on statistics from 2002)
(Danish Ministry of the Environment 2011). Prior to
the land application of sludge, it is either aerobically or
anaerobically digested and then dewatered using a num-
ber of different methods (Jensen and Jepsen 2005).
Sewage sludge is currently not permitted in organic
farming systems in the EU due to concerns about
pathogens, viruses and the possible content of poten-
tially toxic elements (European Communities 2007;
Möller and Stinner 2010). Like other types of organic
wastes, sewage sludge can be a source of nutrients to
enhance soil fertility (Krogh et al. 2001). In particular,
sewage sludge has a high content of phosphorous,
making it a potentially valuable resource, given in-
creasing concerns about ‘peak-phosphorous’ (Cordell
et al. 20 09 ). For example, Table 3 shows that the
phosphorous supply potential of sludge in Denmark
is considerable. However, concerns about the potential
heavy metal and organic contaminant contents of sew-
age sludge have, until now, restricted its use in agri-
culture in general in many countries, whilst in other
countries, e.g. Denmark, a relatively high proportion
of the sewage sludge is land applied as any other
organic fertiliser, complying with low legal thresholds
for heavy metals and other contaminants.
6
Particularly when used as a substrate for plant propagation.
50 Org. Agr. (2013) 3:41–55
The primary risks posed by sewage sludge comprise
heavy metals
7
and organic contaminants.
8
Smith
(2009b) reviewed the concentration data for organic
contaminants (OCs) in sewage sludge and assessed the
potential environmental and health impacts of organic
contaminants in sewage sludge. He notes that according
to the European Commission (2006) there are no
recorded cases of human, animal or crop contamination
due to the use of sludge on agricultural soils following
the provisions of Directive 86/278/EEC. Despite the
international support for recycling sludge to land, the
acceptance of this practice among different European
countries varies considerably and has declined markedly
in some cases, despite the lack of scientific evidence
indicating that it is harmful in any way (Smith 2009b).
Smith’sreview(Smith2009b) indicates that: ‘the pres-
ence of a compound in sludge, or of seemingly large
amounts of certain compounds used in bulk volumes
domestically and by industry, does not necessarily con-
stitute a hazard when the material is recycled to farm-
land’. Concern has also been raised about ‘emerging’
organic contaminants, which might be present in sewage
sludge. Clarke and Smith (2011) conducted therefore a
review of emerging OCs in biosolids (sewage sludge) of
a selection of chemicals of potential concern for land
application based upon human toxicity, evidence of
adverse effects on the environment and endocrine dis-
ruption. Whilst they maintain the view that the most
sustainable option for biosolid use is land application,
they stress that ‘continued vigilance in assessing the
significance and implications of ‘emerging’ OCs in
sludge is necessary to support and ensure the long-
term sustainability and security of the beneficial agri-
cultural route for biosolids management’ (Clarke and
Smith 2011).
A large assessment of the risk of using sewage
sludge as a fertiliser and soil conditioner on agricul-
tural lands was recently conduct ed by the Norwegian
Scientific Committee for Food Safety (Eriksen et al.
2009). The assessment focussed on heavy metals and
organic contaminants as well as potential pharmaceu-
tical contaminants. Based on thei r findings, the assess-
ment panel ‘considers the use of sewage sludge to
constitute a low risk to the soil ecosystem’ (Eriksen
et al. 2009). The panel recommended though that as
the use of sludge has the potential to increase the
concentration of inherent toxic metals, such as cadmi-
um and mercury, the use of sludge on agricultural land
should be monitored.
Other organic waste types
Whilst the potential of sewage sludge has been
discussed above, there is also a future potential for
new sanitation systems that can source separate waste-
water and thus allo w for urine and blackwater to be
harvested separately and used as a nutrient source after
treatment (Winker et al. 2009). The design of integrat-
ed ecological waste management systems to recycle
urine from urban areas is technically feasible and can
lead to increased recycling of nutrients to agricultural
land (Magid et al. 2006). However, the implementa-
tion of such systems should be cost-effective as well as
socially acceptable, both by urban populations as well
as farmers. The colle ction of human urine, which re-
quires a certain type of toilet and collection system,
occurs only to a very limited extent in Denmark.
Therefore, a futur e recycling of urine would require
significant infrastructural changes. Products derived
from domestic wastewater streams can contain organic
micropollutants and thus require treatment (Winker et
al. 2009). Human urine does not generally contain
pathogens that can be transmitted through the environ-
ment; however, one inevitable source of pathogens in
urine collected from the urine diverting toilets is cross
contamination from faeces (Magi d et al. 2006
).
Garden and park waste is a waste type collected
systematically in Denmark which can be recycled fol-
lowing either home or central composting (Boldrin
2009). The amount of nutrients recycled from municipal
collection of both garden and park waste (Table 3)dem-
onstrates a considerable potential. The majority of pro-
duced compost is typically redistributed to home owners
for garden use, whilst it is also increasingly being used
by professional landscapers and gardeners (Boldrin
2009). Utilisation in organic agriculture will therefore
compete with an existing market for garden park com-
post, which may drive prices to an unrealistic level for
organic farmers.
Nygaard Sørensen and Thorup-Kristensen (2011)
conducted an investigation of the fertiliser effects of
‘mobile’ green manures. Mobile green manures are
typical green manures which, instead of being ploughed
7
Heavy metals of concern are primarily cadmium (Cd), lead
(Pb), mercury (Hg), nickel (Ni), zinc (Zn), copper (Cu) and
chromium (Cr).
8
For an overview of organic contaminants, see Table 2 in Smith
(2009b).
Org. Agr. (2013) 3:41–55 51
into the same field, are harvested and applied to other
fields. They found that it is possible to produce mobile
green manures with a high concentration of sulphur (S),
P, K and B. Additionally, they found that the C/N ratio
of the green manure had a strong influence on yields.
Amendments with a high C/N ratio (>20) decreased
yields when compared to inputs with a lower C/N ratio.
If garden park waste, which typically has a high C/N
ratio, should be used as a fertiliser, it would most likely
require the removal of the high C/N ratio fraction (wood
material), which can also be useful as biomass fuel. It
should be noted though that while mobile green
manures may include legumes, which add supple-
mentary nitrogen by fixation, they do not represent
an additional input of the other nutrients at the farm
level; rather, they can be used to shift nutrient avail-
ability between fields.
Acceptability of non-farm organic waste
use in organic agriculture
Technical and legislative requi rements for the future
utilisation of theoretically available organic nutrients
to farmers in Denmark constitute one part of the bar-
rier for increased use of these resources. The social
acceptability, both for organic farmers and consumers,
of the use of organic wastes is an important factor to
understand and address. It would be of scant use
should organic farmers be unwilling to use organic
wastes of certain origin, despite possible consumer
acceptance of the use of organic wastes as fertilisers.
Current food safety concerns, for example regarding
multi-resistant bacteria, do little good in enhancing an
increased acceptability and use of organic wastes
amongst consumers and farmers alike. It is further-
more essential to discuss how the land application of
organic waste products aligns with the principles of
organic agriculture. This section seeks to address these
questions and will deal with the various waste types
individually.
Biogas residue
From a plant nutrition perspective, the potential use of
biogas residue as a crop fertiliser is considered posi-
tive, although the conten t of pollutants should be
closely monitored (Arthurson 2009). However, from
an organic principle perspective, the acceptability of
biogas slurry as a suitable organic fertiliser has been
discussed, prim arily based on the notion that biogas
slurry has a very high mineral N content which might
be contrary to the principles of organic agriculture of
building healthy soils (rather than feeding the plant)
(Tersbøl 2008). However, given the increased focus on
biogas production in organic systems in the past
5 years, coupled with recognition of current and future
challenges related to nutrient and energy supply, the
use of biogas slurry in organic farming in Denmark is
gaining acceptance. This increased acceptance can
also be attributed to the potential yield benefits biogas
residue might provide.
Sewage sludge
Although we are fully aware of the stance taken by
organic agriculture regarding sewage sludge, we
would like to raise the question of whether all sewage
sludge should, in future, still be disregarded as a
nutrient source in organic systems. Legal requirements
about the quality and use of sludge are stringent, partic-
ularly following concerns about the concentration of
organic contaminants. The European Commission’s
opinion is that the best environmental use of sewage
sludge is as an agricultural fertiliser, provided that its use
does not pose a threat to human and animal health as
well as the environment (Smith 2009b).
As discussed above, nutrients in sewage sludge
(and household waste) might by in large come from
conventional agriculture, although ideologically, the
use of sewage sludge aligns with the organic ideology
of working with closed cycles. However, the applica-
tion of the precautionary principle in organic agricul-
ture so far prevents the use of sewage sludge. The
precautionary principle is a broadly applied term in
environmental regulation. According to EU legisla-
tion, the precautionary principle may be invoked
where urgent measures are needed in the face of a
possible danger to human, animal or plant health, or
to protect the environmen t where scientific data do not
permit a complete evaluation of the risk (Commission
of the European Communities 2000). This principle is
applied mainly where there is a danger to public
health. For example, it may be used to stop distribu-
tion or order withdrawal from the market of products
likely to constitute a health hazard. Thus, according to
the EU, there can be no question of merely taking a
negative attitude towards risk.
52 Org. Agr. (2013) 3:41–55
The organic principle of care, one of the four main
principles of organic agriculture, states that: ‘Organic
agriculture should be managed in a precautionary and
responsible manner to protect the health and well-
being of current and future generations and the envi-
ronment’ (Luttikholt 2007). Indeed, the precautionary
principle is central to organic agricultu re concerning
the management of risk, for example preventing the
use of GMO. The precautionary principle places a
burden of proof on those who create potential risks
and requires that activities should be regulated even if
it cannot be shown that these activities are likely to
cause potential harm (Sunstein 2003). Sunstein (2003)
challenges the use of the precautionary principle as a
regulator of risk, stating that, whilst the use of the
principle does not lead us in a bad direction, the problem
is it leads us in no direction at all, primarily claiming that
the principle ‘is literally paralysing—forbidding inac-
tion, stringent regulation and everything in between’.
Although our aim is not to debate the merits and
pitfalls of the precautionary principle, we feel it is
particularly important to assess the implications of its
use. For example, there is a tendency to neglect the
system effects of invoking the precautionary principle,
i.e. that the decision not to utilise a resource such as
sewage sludge will have unintended global effects
such as increased greenhouse gas emissions or envi-
ronmental degradation, e.g. due to phosphorus mining
and sludge incineration, and the long-term use of a
finite resource (phosphorus). As stated above, the
precautionary principle should be applied where sci-
entific data do not permit a complete evaluation of
risk. While a complete risk assessment cannot be
made, since there are some questions that still need
attention (i.e. emerging contaminants that need ad-
dressing), there is an overwhelming body of evidence
indicating that recycling of sewage sludge on farmland
is not constrained by concentrations of inorganic or
organic contaminants found in contemporary sewage
sludge.
A survey of the Danish public’s perception of sew-
age sludge (with 1,028 respondents) was conducted in
2011. Approximately two thirds of the respondents
agreed with the statement that sewage sludge should
be recycled through land application, whilst 70 % of
respondents felt confident that sewage sludge, fulfill-
ing legislative requirements, could be recycled without
risks to humans, animals or the environment (BGORJ
2011). These findings might indicate that consumer’s
concern regarding the use of sludge need not be a
barrier to an increased use of sludge as a nutrient
source.
Conclusion and final remarks
The decision to phase out convent ional nutrients in
Danish organic agriculture might represent a landmark
in the development of organic agriculture. There are
significant lessons which can, both now and in future,
be learnt from this decision, not just for Danish organ-
ic agriculture but also for the international organic
sector. The reasons behind the organic sectors’ deci-
sion are not unique in organic agriculture internation-
ally, although it is difficult to quantify exactly the
reliance of organic agriculture on conventional nutri-
ent supply in o ther countries. Consideration should
thus be given as to whether Denmark should stand
alone following this decision or whether other coun-
tries should follow suit. There are also significant
challenges ahead as a consequence of such a decision.
Ensuring a sustainable nutrient supply to organic
farms in the future will require a rethinking of farmers’
strategies and further require support from all levels in
society. As demonstrated in this article, finding alter-
native strategies to ensure nutrient supply will require
a tapestry of small solutions, which in unison can
ensure that organic agriculture continues to grow
whilst ensuring the integrity of the organic sector.
One of the forefathers of organic agricultu re, Sir
Albert Howard, was a very strong proponent of the
recycling of organic waste (Heckman 2006). One ele-
ment of the tapestry of solutions is to review the
volume and type of nutrient sources available in alter-
native, non-farm organic waste streams. Realising the
potential on offer will require technological and infra-
structural support to varying degrees to facilitate the
collection, treatment and redistribution of organic
wastes. Furthermore, for some waste types, there is a
need for discussion, and perhaps a rethi nking, about
the acceptability of use of such resources. For exam-
ple, whether recycled nutrients from sewage sludge
and organic household waste should be viewed as a
reliance on conventional nutrients. A pessimistic view
of the decision to ban conventional nutrients might be
that it threatens the grow th of the organic sector.
However, the challenges that arise from this decision
do not seem insurmountable, and in the long term,
Org. Agr. (2013) 3:41–55 53
seeking to align organic practices with the organic
principles is very important.
References
Arthurson V (2009) Closing the global energy and nutrient
cycles through application of biogas residue to agricultural
land—potential benefits and drawbacks. Energies 2(2):226–
242
Birkmose T (2007) Digested manure is a valuable fertilizer.
European Biogas Workshop: The Future of Biogas in
Europe III. pp. 89–94
Birkmose T. (2009) Nitrogen recovery from organic manures:
improved slurry application techniques and treatment—the
Danish scenario. Paper presented to the International Fertiliser
Society Conference, Cambridge, 2009. Proceedings 656.
International Fertilizer Society .
Boldrin A. (2009) Environmental assessment of garden waste
management. PhD Dissertation; Technical University of
Denmark.
Boldrin A, Christensen TH (2010) Seasonal generation and
composition of garden waste in Aarhus (Denmark). Waste
Manage 30(4):551–557
Boldrin A, Neidel TL, Damgaard A, Bhander GS, Møller J,
Christensen TH (2011) Modelling of environmental im-
pacts from biological treatment of organic municipal waste
in EASEWASTE. Waste Manage 31:619– 630
Brady NC, Weil RR (1999) The nature and property of soils,
12th edn. Prentice Hall, Upper Saddle River
Bulluck LR, Brosius M, Evanylo GK et al (2002) Organic and
synthetic fertility amendments influence soil microbial,
physical and chemical properties on organic and conven-
tional farms. App Soil Ecol 19(2):147–160
Clarke BO, Smith SR (2011) Review of emerging organic
contaminants in biosolids and assessment of international
research priorities for the agricultural use of biosolids.
Environ Int 37(1):226–247
Cordell D, Drangert JO, White S (2009) The story of phospho-
rus: global food security and food for thought. Global
Environ Chang 19(2):292–305
Dalgaard T., Haugaard H, Jørgensen U et al. (2009) Synergies
between the expansion of biogas production and organic
farming. Paper presented at NJF Seminar 428: Energy
conversion from biogas production.
Danish Ministry of the Environment (2009) Spildevandsslam fra
kommunale og private renseanlæg i 2005 [Sewage sludge
from municipal and private wastewater treatment plants for
2005]. Orientering fra Miljøstyrelsen Nr. 3. Danish Ministry
of the Environment.
Danish Ministry of the Environment (2011) Affaldstatistik 2009
og Fremskrivning af affaldsmængder 2011–2050. [Waste
statistics 2009 and projections of waste amounts for 2011–
2050]. Orientering fra Miljøstyrelsen Nr. 4. Danish Ministry
of the Environment.
Davis J, Abbott L (2006) Soil fertility in organic farming systems.
In: Kristiansen P, Taji A, Reganold J (eds) Organic agricul-
ture: a global perspective. CABI, Wallingford, pp 25–51
Diacono M, Montemurro F (2010) Long-term effects of organic
amendments on soil fertility. A review. Agron Sustain Dev
30(2):401–422
Edmeades DC (2003) The long-term effects of manures and
fertilisers on soil productivity and quality: a review. Nutr
Cycl Agroecosys 66(2):165– 180
Eriksen GS, Amundsen CE, Bernhoft A, Eggen T, Grave K,
Sørensen BH, Källqvist T, Sogn T, Sverdrup L (2009) Risk
assessment of contaminants in sewage sludge applied on
Norwegian soils: Opinion of the panel on contaminants in
the Norwegian Scientific Committee for food safety.
Norwegian Scientific Committee for Food Safety (VKM)
European Commission (EC). (2006) Report from the commis-
sion to the council and the European Parliament on the
implementation of community waste legislation for the
period 2001–2003. European Commission.
European Communities (2007) Council Regulation (EC) No
834/2007 of 28 June 2007 on organic production and
labelling of organic products and repealing Regulation
(EEC) No 2092/91. Off J Eur Union 50(L189):1–23
Evanylo G, Sherony C, Spargo J et al (2008) Soil and water
environmental effects of fertilizer-, manure-, and compost-
based fertility practices in an organic vegetable cropping
system. Agr Ecosys Environ 127(1–2):50–58
Farrell M, Jones DL (2009) Critical evaluation of municipal
solid waste composting and potential compost markets.
Bioresource Technol 100(19):4301– 4310
Fog E. (2010) Biogas og økologisk landbrug - en god cocktail
[Biogas and organic agriculture—a good cocktail]. The
Knowledge Center for Agriculture. Danish Agricultural
Advisory Services
Frederiksen P, Langer V (2004) Localisation and concentration
of organic farming in the 1990s: the Danish case. Tijd Econ
Soc Ge 95(5):539–549
Gerba CP, Tamimi AH, Pettigrew C et al (2011) Sources of
microbial pathogens in municipal solid waste landfills in
the United States of America. Waste Manage Res 29(8):781–
790
Hargreaves JC, Adl MS, Warman PR (2008) A review of the use
of composted municipal solid waste in agriculture. Agr
Ecosys Environ 123(1–3):1–14
Heckman J (2006) A history of organic farming: transitions
from Sir Albert Howard’s war in the soil to USDA National
Organic Program. Ren Agr Food Syst 21(03):143–150
IFOAM (2005) The IFOAM Basic Standards for Organic
Production and Processing. IFOAM
Jensen J, Jepsen SE (2005) The production, use and quality of
sewage sludge in Denmark. Waste Manage 25:239–247
Jørgensen KF, Kristensen E. (2010) Fælles strategi for
udfasning af konventionel gødning og halm i økologisk
landbrugsproduktion [Common strategy for the phasing
out of manure and straw i organic agriculture]. Organic
Denmark and Danish Agriculture and Food Council.
Kirchmann H, Nyamangara J, Cohen Y (2005) Recycling mu-
nicipal wastes in the future: from organic to inorganic
forms? (Special issue: nutrient management in sustainable
agricultural systems.). Soil Use Manage 21:152–159
Kirchmann H, Ryan MH, Bergstrom L (2007) Plant nutrient use
efficiency in organic farming—consequences of exclusive
use of organic manures and untreated minerals. CAB Rev:
Perspect Agricul Vet Sci, Nutr Natural Res 2(076):12
54 Org. Agr. (2013) 3:41–55
Krogh PH, Jensen J, Tybirk K (2001) Slam på marken [Sludge
in the field]. In: Petersen J, Christensen PB, Fenger J et al
(eds) Natur.dk - Natur og Miljø i Danmark. Danmarks
Miljø Undersøgelse, Aarhus University, Aarhus
Kyed S, Kristensen IS, Tvedegaard N. (2006) Gødning og Halm i
økologisk Jordbrug: Fokusområde 2004–2005. [Manure and
straw in organic agriculture: focus 2004–2005]. Report,
Organic Denmark
Luttikholt LWM (2007) Principles of organic agriculture as
formulated by the International Federation of Organic
Agriculture Movements. NJAS - Wagen J Life Sc 54(4):
347–36 0
Magid J, Eilersen AM, Wrisberg S, Henze M (2006)
Possibilities and barriers for recirculation of nutrients and
organic matter from urban to rural areas: a technical theo-
retical framework applied to the medium-sized town
Hillerod, Denmark. Ecol Eng 28:44–54
Ministry of Economic and Business Affairs Denmark. (2009)
Grøn Vækst (Green Growth). Ministry of Economic and
Business Affairs Denmark.
Ministry of Food Agriculture and Fisheries. (2008) Vejledning
om gødsknings- og harmoniregler [Guidelines for regu-
lations of fertilising and harmony rules]. Ministry of
Food, Agriculture and Fisheries, The Danish AgriFish
Agency
Möller K, Stinner W (2010) Effects of organic wastes digestion
for biogas production on mineral nutrient availability of
biogas effluents. Nutr Cycl Agroecosys 87(3):395–413
Nygaard Sorensen J, Thorup-Kristensen K (2011) Plant-based
fertilizers for organic vegetable production. J Plant Nutr
Soil Sci 174:321–332
Odlare M, Arthurson V, Pell M et al (2011) Land application of
organic waste—effects on the soil ecosystem. Appl Energ
88(6):2210–2218
Pang XP, Letey J (2000) Organic farming: challenge of timing
nitrogen availability to crop nitrogen requirements. Soil Sci
Soc Am J 64(1):247–253
Plantedirektoratet. (2010) Vejledning om økologisk
jordbrugsproduktion [Guidelines for o rganic agricultural
production]. Ministry of Food, Agriculture and Fisheries
Quilty JR, Cattle SR (2011) Use and understanding of organic
amendments in Australian agriculture: a review. Aust J Soil
Res 49(1):1–26
Smith SR (2009a) A critical review of the bioavailability and
impacts of heavy metals in municipal solid waste composts
compared to sewage sludge. Environ Int 35(1):142 –156
Smith SR (2009b) Organic contaminants in sewage sludge
(biosolids) and their significance for agricultural recycling.
Philos T R Soc A 367(1904):4005–4041
Soil Association. (2010) Soil Association organic standards for pro-
ducers. Rep. Revision 16.3 November 2010. Soil Association.
Stockdale EA, Shepherd MA, Fortune S et al (2002) Soil fertil-
ity in organic farming systems—fundamentally different?
Soil Use Manage 18:301–308
Sunstein CR (2003) Beyond the precautionary principle. U Penn
Law Rev 151(3):1003–1058
Tersbøl M (2008) Energi- og gødningsforsyning ved hjælp af
biogas [Energy and fertilizer supply from biogas]. In: Alrøe
H, Halberg N (eds) Udvikling, vækst og integritet i den
Danske økologisektor [Development, growth and integrity
in the Danish organic sector. A knowledge synthesis on the
opportunities and barriers for a continued development and
market-based growth in production, processing, and sale of
organic products.]. ICROFS, pp. 429–448
Tersbøl M. (2009) Økologisk biogas - Hvorfor og hvordan?
[Organic biogas—why and how?]. Økologisk Landsforening,
Organic Denmark
Thorup-Kristensen K, Magid J, Jensen LS (2003) Catch crops
and green manures as biological tools in nitrogen manage-
ment in temperate zones. Adv Agron 79:227–302
Thorup-Kristensen K, Dresbøll DB, Kristensen HL (2012) Crop
yield, root growth, and nutrient dynamics in a conventional
and three organic cropping systems with different levels of
external inputs and N re-cycling through fertility building
crops. Eur J Agron 37:66–82
Tvedegaard N. (2007) Et økologisk jordbrug uden konventionel
husdyrgødning og halm - gårdsrapporter. [Organic agricul-
ture without conventionel animal manure and straw].
Report prepared for Organic Denmark
von Fragstein und Niemsdorff P, Kristiansen P (2006) Crop
agronomy in organic agriculture. In: Kristiansen P, Taji
A, Reganold J (eds) Organic agriculture: a global perspec-
tive. CABI, Wallingford, pp 53–82
Winker M, Vinnerås B, Muskolus A, Arnold U, Clemens J (2009)
Fertiliser products from new sanitation systems: their poten-
tial values and risks. Bioresour Technol 100:4090–4096
Org. Agr. (2013) 3:41–55 55
