Agriculture, Ecosystems and Environment 90 (2002) 139–153
The role of livestock for sustainability in mixed farming: criteria
and scenario studies under varying resource allocation
J.B. Schiere a , M.N.M. Ibrahim b,∗ , H. van Keulen c
a
Animal Production Systems Group, Wageningen Institute of Animal Sciences (WIAS), Wageningen Agricultural University, P.O. Box 338,
6700 AH Wageningen, The Netherlands
b Department of Animal Science, Faculty of Agriculture, University of Peradeniya, Peradeniya, Sri Lanka
c Research Institute for Agrobiology and Soil Fertility (AB-DLO), P.O. Box 14, 6700 AA Wageningen, The Netherlands
Received 8 November 1999; received in revised form 30 January 2001; accepted 30 January 2001
Abstract
Cropping, when possible, tends to become more important than animal production because, in general, it can feed more
people per area unit in terms of calories and protein. In such systems, the role of wasteland grazing as a source of energy
for agriculture through animals for traction and dung is often taken over by the use of resources from fossil reserves. This
changing role of animals in the sustainability of agriculture is addressed in this paper to discuss options and constraints for
animal production in newly developing farming systems. Based on a brief literature review, this paper discusses how and in
which way ruminant livestock has played or can continue to play a role in (newly developing forms of) sustainable agriculture.
The role of livestock in different modes of agriculture ranging from expanded agriculture (EXPAGR), and high external inputs
agriculture (HEIA) to low external inputs agriculture (LEIA), and new conservation agriculture (NCA) are elaborated. It is
argued that even when fossil reserves based external inputs such as oil and fertilisers become more widely used, they should
still be used with care to save money and finite resources as well as to avoid problems of waste disposal. However, in conditions
with limited access to resources, it continues to be difficult to obtain inputs from fossil reserves. Under these conditions, the
major options to increase system sustainability by reducing pollution problems and dependency on external resources are (a)
to adjust ways and objectives of production systems to the access to resources, and (b) to achieve increased use and recycling of
resources within the system itself. Definitions for sustainability are given and translated into four criteria, i.e. food production
and degree of self-sufficiency in the short term based on energy, protein, clothing, shelter, etc.; food production and degree of
self-sufficiency in the long term expressed in the form of soil organic matter (SOM) content; reduced dependence of external
inputs (=nitrogen use); and aspects of resilience, stability and equity in crop–livestock systems. The results of scenario studies
concerning use of grass and legume leys for livestock production illustrate options and trade-offs for different crop–livestock
combinations in terms of these criteria for sustainability. © 2002 Elsevier Science B.V. All rights reserved.
Keywords: Crop–livestock systems; Sustainability; Food production; Resource fluxes
1. Introduction
∗ Corresponding author. Tel.: +94-8-387180;
fax: +94-8-388041.
E-mail address: [email protected] (M.N.M. Ibrahim).
Traditionally, animals and particularly ruminants
were an asset to society by converting biomass from
vast grazing areas into products useful for humans,
e.g. dung, draught, milk, meat and security. However,
0167-8809/02/$ – see front matter © 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 1 6 7 - 8 8 0 9 ( 0 1 ) 0 0 1 7 6 - 1
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J.B. Schiere et al. / Agriculture, Ecosystems and Environment 90 (2002) 139–153
growing human populations cause increased and
shifting demands for food and other products. This
results in the conversion of natural forests and grazing
land into arable land for crop and fodder production,
thus leading to quantitative and qualitative changes
in biomass availability for human food and livestock
feed (Winrock, 1978). Where cropping is possible, it
can feed more people in terms of calories and protein
than what is possible with animal production. This
is shown in Table 1 (Spedding, 1979) with data for
specific conditions that reflect the general principle.
However, there are soils and climates where cropping
is not very successful or very risky such as on the
wet peat soils in Western Europe, in high mountain
ranges or in arid regions (Fig. 1).
Apart from their inferior caloric output, compared
to crops, animals are also associated with deforestation and erosion (Durning and Brough, 1991).
However, historically, deforestation tended to start in
response to the requirement for timber for fuel and
construction (Ponting, 1991). Forest was cultivated
with crops and grassland for food production through
shifting cultivation, permanent cropping or simply
as a method of occupying land (Ruthenberg, 1980;
Table 1
Approximate number of people fed per hectare of land in areas
where cropping is possible (adapted from Spedding, 1979)
Protein
Energy
Crops
Maize (Zea mays)
Wheat (Triticum aestivum)
Rice (Oryza sativa)
Potatoes (Solanum tuberosum)
5.2
6.3
7.0
9.5
10.4
8.4
14.0
16.5
Livestock
Chicken meat
Lamb meat
Beef
Pork
Milk
2.5
1.0
1.0
1.4
3.0
1.0
1.0
1.0
2.0
2.5
Poelhekke, 1984; Hecht, 1993). In the present day, the
strong argument against keeping of livestock is that the
requirement for cropland is increasing through expansion of grain-based beef, dairy and poultry production
in the USA, Western Europe, in peri-urban dairies of
developing countries, and recently in the Pacific Rim
and China (Winrock, 1978). Combined with changing
human food patterns, this has increased the demand
Fig. 1. Carrying capacity in terms of human population based on crop and animal production in areas where cropping is possible (adapted
from Spedding, 1979).
J.B. Schiere et al. / Agriculture, Ecosystems and Environment 90 (2002) 139–153
for crop land relative to grazing land (Alexandratos,
1988). As a result, even marginal grazing areas are
converted into crop land and overgrazing of the remaining areas becomes the rule rather than the exception (Jodha, 1986). Land scarcity starts to occur, even
in pastoral areas. This upsets existing ethnic balances,
and can result in animosity between pastoralists and
arable farmers who peacefully co-existed to mutual
benefit in the past (Powell and Waters-Bayer, 1985;
Grijseels, 1988).
The use of external inputs can increase the carrying capacity of some range-land systems (Breman and
De Wit, 1983). However, such external inputs are not
available or not affordable to all farmers. Hence, over
exploitation (i.e. mining) of land without the use of
external inputs tends to be the result (Van Der Pol,
1992). This threatens the sustainability of these systems, which is defined here in simple terms as “the
capacity to continue production”. Too liberal use of
external inputs, on the other hand, causes waste disposal problems or increased political dependency on
external supplies (De Haan et al., 1997; Schiere and
van Keulen, 1999).
In general, animals are often considered to be the
cause for unsustainability in both high and low external input agricultural systems (HEIA and LEIA). In
LEIA, animals are blamed for scavenging whatever is
left, and in HEIA, the role of animals as waste utilisers has been reverted to a role as polluters and converters of prime resources. Rather than being an asset
to sustainability, livestock keeping has become a liability (Durning and Brough, 1991; Kaasschieter et al.,
1990; Rifkin, 1992).
The objective of this paper is to show that livestock
can play a positive role in sustainable systems. The
paper reassesses the controversial role of animals in
sustainable agriculture based on scenario studies and
literature. Specific objectives are (1) to describe a set
of historical conditions where livestock has been essential for the sustainability of existing farming systems, particularly in mixed crop–livestock systems, (2)
to outline a classification of livestock farming systems
that ranges from predominantly animal production via
mixed crop–livestock systems to predominantly crops
at different ratios of relative access to land, labour and
capital and (3) to provide some definitions and criteria for sustainability that can be operationalised in
scenario studies.
141
2. Livestock and sustainability of
agricultural systems
2.1. Role of livestock
Livestock, and particularly ruminants, traditionally
graze on natural pasture, forest areas, roadsides, fallow lands, crop re-growth or crop residues such as
straws, brans, oilseeds, and other by-products. When
abundant feed is available, livestock can be considered
a form of wealth, power and security, a perception
based on the conversion of solar energy captured in
biomass into products valuable for human society.
Therefore, not surprisingly, strong linguistic links
between the words for cattle and capital exist in languages all over the world (Schiere, 1995). For example, the Spanish ‘ganado’ is related with ‘ganar’, and
similar relations exist in African and Asian languages.
Indeed, under conditions of abundant biomass, cattle
were often a decisive factor in the survival (sustainability) of a system. However, ways and objectives of
keeping livestock are changing as a cause and result of
changing access to feed (Crotty, 1980; Palthe, 1989;
De Leeuw and Rey, 1995; Schiere, 1995; Ifar, 1996).
Often, animal production is associated with problems
of unsustainability. This may be true in some cases,
in others it is definitely not.
2.2. Benefits of livestock
Livestock were components of systems with long
term sustainability. For example, the keeping of livestock was essential for survival in divergent systems
such as those of the pastoralists in Africa, and those
on peat soil pastures of the low countries and on
mountain ranges unsuitable for cropping. Animals
have long been essential in sustaining crop yields in
the infield–outfield systems of Western Europe and
other parts of the world, where dung and draught
from wasteland grazing (outfields) was used for crop
cultivation on the infields around the homesteads
(Chayanov, 1926; Willerding, 1980; Bieleman, 1987).
In a more intricate way, animals helped to sustain
crop yields by increasing the rate of nutrient flows
in the mixed crop–livestock systems of the Norfolk
and the Flemish systems (Slicher van Bath, 1963),
or by allowing farmers to include crops that either fix atmospheric nitrogen, release immobilised
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phosphorus, or enhance soil organic matter (SOM,
Hoffland, 1991).
Grazing by livestock usually follows rather than
precedes deforestation and/or cropping. In fact, animals, such as the goat, are one of the last means of
survival for large numbers of poor people on bare, exhausted, and/or arid lands. However, in spite of the
importance of animals for the poor classes of farmers,
the advocates for continued animal production on exhausted soils should acknowledge that livestock can tip
the final balance in delicate ecosystems (Schiere and
Grasman, 1997). Interestingly, Jodha (1986) notices
that in the Nepalese hills, the goat can even be an
indicator of unsustainability.
The following section provides a conceptual
framework to indicate when and where livestock
can play a beneficial role in enhancing system
sustainability.
3. Conceptual framework to address livestock
and system sustainability
Age-old systems can become unsustainable under
changing conditions, alternatives and different objectives of production may be required for survival of the
existing population (Hayami and Ruttan, 1985; Van
Der Ploeg and Long, 1994; Schiere and De Wit, 1995).
In that context, shortages of food and feed biomass, or
even threats to sustainability can be tackled by a variety of methods (Boserup, 1965; Ruthenberg, 1980;
Palthe, 1989; Schiere, 1995) as follows:
1. expansion of cultivated land through migration or
shortened fallow cycles;
2. adjustment of consumption patterns and/or population growth;
3. increased recycling of scarce resources;
4. reliance on (liberal) use of external inputs;
5. a combination of (1), (2), (3) and/or (4).
Based on the above biophysical strategies, it is
possible to classify farming systems. The classification presented in Table 2 is based on a matrix in
which population density, access to land and inputs
change relative to each other. In more common terms,
the classification is based on the relative availability of the production factors land, labour and capital
(Schiere and De Wit, 1995).
3.1. Matrix to classify crop–livestock systems
The vertical columns of the matrix reflect the
degree of mixing between animals and crops, from
predominantly livestock, via mixed systems to predominantly crops (Table 2). The horizontal rows
represent four major modes of agriculture that tend
to succeed gathering and hunting. The modes of
agriculture are explained as follows.
• Expansion agriculture (EXPAGR), where land is
abundant, i.e. where shortage of land or local fertility is overcome by migration or expansion into
other regions (Ponting, 1991).
• Low external input agriculture (LEIA), where shortage of land cannot be overcome by migration. Lack
of access to external inputs (capital) implies that
only increased use of labour and skills offers a way
out. This in turn implies modified practices, where
demand is adjusted to resource availability (Schiere
and De Wit, 1993). If not managed properly this can
result in mining of soils and/or collapse of systems
(Van Der Pol, 1992; Schiere and Grasman, 1997).
• High external input agriculture (HEIA), based on
high fluxes of external resources such as in the green
revolution. Basically, in this mode, the demand for
output determines use of inputs (Schiere and De
Wit, 1993). The use of external resources can reach
such high levels that the environment is affected
by emissions from the crop and/or animal production systems, ultimately leading to waste/disposal
problems, and also over-dependence economically
(Kaasschieter et al., 1990; Rerat and Kauchik, 1995;
De Haan et al., 1997; De Wit et al., 1997; Schiere
and van Keulen, 1999; Van Keulen et al., 1999).
• New conservation agriculture (NCA), is a mode
of farming where production goals are matched as
close as possible to the resource base. This approach represents a mix between HEIA and LEIA,
and may be the archetype reasoning behind ecological farming (Altieri, 1991; Kingwell and Pannell,
1987; NRC, 1989; Van Keulen et al., 1999).
3.2. Options and constraints of mixed
crop–livestock systems
This paper focuses on the options and constraints
of increasing the sustainability of mixed systems by
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utilising the animal component. Table 2 addresses
both pastoral and pure crop systems, but it also emphasises the mixed crop–livestock system. This was not
addressed in the classification of Durning and Brough
(1991). The latter argue against pastoral systems
with associated overgrazing and against specialised
systems with associated waste disposal problems.
Unfortunately, they insufficiently explain and explore
the advantages of the mixed crop–livestock systems
in terms of opportunities for waste recycling and for
optimal use of resources available on and between
farms. The following section discusses the constraints
and options in the design of mixed crop–livestock systems of the NCA mode. Importantly, mixing can occur within and between farms and this implies a high
degree of integration of functions rather than mere
diversification, where livestock and crops exist side
by side without being related to a significant extent.
4. Changing relations between crops
and livestock
The main relations between crops and livestock
in mixed systems are simply depicted in Fig. 2. External resources such as solar energy, inherent soil
Fig. 2. A generalised diagram with resource flows in a mixed
crop–livestock system.
fertility/nutrient deposits and rain are depicted in the
central box of the top row. From there, the resources
flow to either a short term deposit on the right, representing biomass in forests, roadsides and grazing
areas, to long term stocks on the left representing
fossil reserves from which “industrial” inputs such
as “improved” seeds and fertilisers are also manufactured, or they flow directly to the crop system. The
livestock subsystem, on the right “feeds” mainly on
short term biomass deposits. The crop sector “feeds”
directly on solar energy, inherent soil fertility, on long
term deposits and/or indirectly on short term reserves
that provide power and nutrients through livestock.
The crossed broken lines are included to indicate
that livestock can “feed” on inputs of fossil reserves through medicines, steel tools, etc. Livestock can
further obtain food from cropping in the form of crop
residues, failed crops and fodder production from
leys, i.e. cultivated fallow. Feed resources from the
cropping sector in mixed systems play an important
role, since in NCA they replace waste land grazing
from EXPAGR as a source of feed in NCA (Table 2).
The boxes “losses” indicate that not all resources are
transformed into a form that is directly beneficial to
human society (Fig. 2).
The relative importance of resource flows between
crops and livestock changes as systems move from
one row to another in the matrix, or even between
columns (Table 2). This is illustrated with a qualitative discussion of the changes in resource flows when
mixed crop–livestock systems move from EXPAGR
to HEIA (Fig. 3A) and from HEIA to NCA (Fig. 3B).
The thickness of the arrows in the diagrams indicates
whether a flow increases or decreases relative to its
original value. For example, the bold arrow from fossil resource deposits to crops in Fig. 3A indicates that
this flow is more important in HEIA than in EXPAGR.
Fig. 3A thus shows that the importance of energy and
resource flows in biomass provided to livestock from
grazing land tends to decline as access to fossil fuel
increases. In other words, fertilisers and fossil fuel
replace dung and animal draught when the system
moves from EXPAGR to HEIA. This change is associated with increased losses from the crop systems,
which initially may not pose a concern as resources
are cheap and waste disposal is not immediately
problematic. Another aspect of this change is that the
crop and the livestock components, when restricted to
J.B. Schiere et al. / Agriculture, Ecosystems and Environment 90 (2002) 139–153
145
Fig. 3. Influence of mode of agriculture on resource flows in mixed farming systems. (A) Resource flows when mixed systems move from
EXPAGR to HEIA. (B) Resource flows when mixed systems move from HEIA to NCA. See Table 2 for definitions of EXPAGR, HEIA
and NCA.
specialised farms, become independent of each other
under increasing (fossil reserve based) resource flows.
A peculiar case is the flow of livestock feed from
crop by-products (i.e. bran from cereal grain and cake
(residue after oil extraction) from oil seed crops). It
tends to increase at the macro scale because cropping intensifies, leading to production of more crop
by-products (Kelley and Parthasarathy, 1994; Joshi
et al., 1994). However, the on-farm availability of bran
and cakes (i.e. crop by-products) is likely to decrease
particularly on small and resource poor farms due to
increasingly centralised grain/oilseed processing.
The case in Fig. 3B represents an idealised situation
where farming moves from HEIA to NCA. Biomass
from grazing areas remains a minor source of feed or
even continues to decline. The major change is the
reduced use of resources based on fossil fuel, due to
either high prices of these inputs and/or problems of
waste disposal. Use of crop residues for animal feed
and of dung and urine for cropping ideally increases
together with the on-farm use of crop by-products
(brans/oilseed cakes). This helps to keep nutrients and
income opportunities in the local system, while allowing animal production on a basal diet of low quality feeds. It is difficult to substantiate, but it may be
assumed that labour requirements for enhanced and
more judicious resource recycling increase in such
system (Chancellor, 1981; Boonman, 1993). Essential in the current analysis is the increased potential
for use of leys when systems move to NCA. A ley is
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defined here as a fallow with planted forages in the
form of alley cropping, catch crops or grass/legume
pastures (Janssen, 1991; Boonman, 1993). Ley crops
may serve a variety of purposes. Tree or cover crops
can reduce run-off and erosion, while providing fuel,
timber, etc. (Kang and Reynolds, 1989). Catch crops
can prevent leaching of nutrients, and legumes can
save on external resources by fixing nitrogen from the
air. Other crops such as certain legumes (Stylosanthes
sp.), grasses (Andropogon sp.) or Cruciferae (mustard seed) stimulate mobilisation of phosphate reserves
from the soil (Hoffland, 1991). The principal role of
livestock in NCA is to convert biomass from leys,
bunds, alleys and catch crops into economically valuable products, and to increase flow rates of available
nutrients (Bosma et al., 1994; Stangel, 1995; Aarts
et al., 1999). These aspects of crop–livestock integration for increased sustainability are discussed in the
following section.
5. Modelling for sustainability
Most definitions of sustainability commonly focus
on compromises among conflicting interests (WCED,
1987; Francis et al., 1990; De Wit et al., 1995; Schiere
and Grasman, 1997).
New insights from the theory on complex systems
show that such a definition is bound to be open to multiple interpretations, and efforts at achieving an objective standard are therefore unlikely or even impossible
to succeed (De Wit et al., 1995). Conway and Barbier
(1990) supplement the above definition by emphasising that sustainability needs to be maintained ‘in the
face of stress or shock’. This specifically refers to aspects of system dynamics and the link with concepts
from ecology. However, this aspect of sustainability
needs translation into measurable criteria/parameters
for practical planning and farm design (Checkland,
1991). A set of four criteria are proposed as shown
below. Threshold values are likely to differ as a function of the prevailing conditions in space and time.
1. Degree of self-sufficiency in the short term (FOOD
PLUS), expressed as the number of people fed from
a given area unit, specified in energy and protein
requirements. The affix PLUS indicates that agriculture provides not only calories and protein, but
also clothing, shelter, etc. The part of FOOD PLUS
that exceeds subsistence requirements, can be sold
or exchanged for other goods.
2. Degree of self-sufficiency in the long term, expressed in terms of SOM content. This assumes
that land quality in terms of chemical fertility and
physical structure is related to SOM content. No
generally accepted standards for organic matter
quantity and quality have been formulated (which,
in view of the current discussion, would be practically impossible), but for West Africa, Feller et al.
(1991) have suggested threshold levels for SOM
as a function of soil texture to maintain physical
and chemical soil fertility.
3. Minimum, though not necessarily zero, use of external inputs, here expressed in terms of nitrogen
use. The choice for nitrogen is debatable because
(atmospheric) nitrogen can be considered a renewable resource, whereas phosphorus or potassium
availability depends on fossil (finite) supplies. In
that sense, resources such as water or fossil energy
might also be more appropriate, but nitrogen is used
here since it is very essential for life and because the
reasoning can easily be extended to other nutrients.
4. Criteria derived from system dynamics: sustainability in the face of stress or shock. These aspects
cover concepts such as system resilience, stability
and equity (Conway, 1986; Holling, 1973; Pannell
and Bathgate, 1991; Morrison et al., 1986). Quantification of these concepts is not attempted, but
their importance is discussed.
6. Scenario studies
6.1. Methodology
6.1.1. Modelling approaches
Several modelling approaches and software packages are available for feed allocation and simulation
of livestock systems. A number of scenario studies
was carried out at the Department of Animal Production Systems of the Wageningen Agricultural University, The Netherlands by using different approaches,
i.e. linear programming (LP) (Kater, 1989; Bos, 1991;
Insiani, 1990) and a combination of spreadsheets and
dBase (Kaasschieter et al., 1990). Linear programming
(resource maximisation matrix) was used in many of
J.B. Schiere et al. / Agriculture, Ecosystems and Environment 90 (2002) 139–153
147
the above studies because it is specifically designed
for resource allocation, and it provides a convenient
platform for interdisciplinary discussion. Also LP can
do resource allocation over time and space with no
difficulty other than an expanded matrix size. Linear
programming is often understood to give one solution
rather than a range, but this issue was overcome by
running the model several times. The studies aimed at
exploring options and constraints, rather than predictions, for crop–livestock integration for more sustainable forms of agriculture.
6.1.2. Approaches to evaluate the FOOD
PLUS criteria
The following four approaches were taken.
1. The output of the farm system was maximised for
FOOD PLUS at a set of predetermined crop/ley
ratios ranging from 100% crop to 100% ley. This
resulted in a series of points that formed a response curve as in Fig. 4, an approach also followed by Renkema (1972), Morrison et al. (1986),
Kingwell and Pannell (1987) and Schiere et al.
(1999).
2. Losses that are either inherent to the process or
are the result of inappropriate management/design
were ignored, although they can be quantified and
incorporated in more detailed modelling.
3. The scenarios for sustainable crop–livestock systems were examined through sensitivity analysis,
based on realistic standard values, rather than on
data collected for a particular case that cannot be
extrapolated to other contexts.
4. The model assumed that a completely vegetarian
diet was possible at 100% crops and that a diet
consisting of only animal products was possible
at 100% ley. This simplification allowed the exploration theoretical extremes. Pastoral tribes in
Africa are known to survive almost entirely on
animal produce, and vegetarians survive well without any food from animal origin (Spedding, 1979;
Reader, 1988).
Although several aspects need further research (e.g.
labour or draught requirements, the effect of livestock
on nutrient dynamics, or the use of livestock for security or savings, or even the effect of seasons or indivisibility of production factors), the results provide a
useful framework for further discussion and research.
Fig. 4. The behaviour of farm systems consisting of a series of
ratios of crops and ley with and without livestock in relation
to criteria 1–3 (see text). In (a), the broken lines a1 and a2
indicate that the curvature of line A B is variable, but that the
combination crops and livestock can achieve higher total FOOD
PLUS than crops alone. FOOD PLUS is defined as the degree of
self-sufficiency for energy, protein, and clothing, shelter, etc. In
(b), SOMG and SOML are points at which the graminae/grass and
legume ley lines intersect the X-axis, respectively (see text).
6.2. Results and discussion
The results of the scenario studies are simplified and
summarised in Fig. 4a–c, where the horizontal axis
represents the percentage ley in the system. The ley
can consist of either grass, legumes or a mix of the two.
The vertical axis in Fig. 4a represents the number of
people that can be fed (FOOD PLUS), based on energy
and protein requirements. The vertical axis in Fig. 4b
and c represent the SOM balance and the need for external nitrogen, respectively, simplified and assumed
to be linear following Kaasschieter et al. (1990). Fig. 5
shows how the case of Fig. 4 is likely to develop over
time, i.e. it suggests that the negative SOM balance
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from animal produce are assumed to be 5 and 10 times
as high as from crops. The results are discussed below in relation to practical observations from field
conditions.
Fig. 5. The production of FOOD PLUS over time (solid lines refer
to crop production only, broken lines to mixed cropping systems).
The t0 , t10 and tn denote short, medium and long term, respectively.
FOOD PLUS is defined as the degree of self-sufficiency for energy,
protein, and clothing, shelter, etc.
at the left-hand side of the X-axis in year ‘0’ translates into lower FOOD PLUS over years to come.
Fig. 6 shows how farm income varied at different levels of subsistence needs and when the price of nutrients
Fig. 6. Effect of crop–livestock integration on-farm income if
surplus production above different levels of subsistence needs can
be sold, and where FOOD PLUS from animals is sold at five times
as much as those of crops. The dotted lines AB and A B refer
to crop production and crop–livestock systems, respectively (see
text). FOOD PLUS is defined as the degree of self-sufficiency for
energy, protein, and clothing, shelter, etc.
6.2.1. FOOD PLUS
Cropping alone at any given time for system selected for the present study provided more FOOD
PLUS than animals on fallow grazing or ley (Fig. 4a).
Thus, cropping supported a larger population in the
short term than 100% ley (Fig. 4a: lines AB and
A B ). In this highly simplified reasoning, the line
AB for crops without livestock in Fig. 4a declined
linearly with an increasing proportion of ley in the
rotation, purely because humans are not assumed to
eat grass. However, the point A is likely to become
lower over time as decreasing soil fertility associated
with lower SOM levels in the absence of fallow/ley,
results in lower crop yields. This is a typical example of a trade-off between short and long term
food security, i.e. between FOOD PLUS and SOM
(Table 2). As the SOM balance becomes positive at
increasing proportions of ley (Fig. 5), crop yields over
time are sustained. Eventually, the line A B is hypothesised to assume the curvilinear shape, implying
that in the long term, the combination of crops and
livestock can support more people than either of the
components alone.
Inclusion of livestock (milk, meat) products
(Fig. 4a: line A B ) allows in principle also to feed
more people than crops alone (Fig. 4a: line AB). Animals utilise crop by-products such as brans, broken
grains, oil seed, cakes, stovers and straws (Sundstøl
and Owen, 1984; Joshi et al., 1994), but they start
to increasingly use fodder as the proportion of ley
increases along the X-axis. The effect of inclusion of
livestock in a crop system on FOOD PLUS, i.e. the
distance between lines AB and A B , depends on as
follows.
• The requirements of humans for (animal) protein.
When these are high relative to the energy needs,
the system will even use food (grains) for animal
feed to generate more animal protein, thus reducing
total FOOD PLUS (Kater, 1989).
• The quality of the crop residues and ley. Total
output of milk and meat from livestock is low
when only straw and stovers with low digestible
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energy contents are available. In that situation, the
distance between lines AB and A B is small, ignoring the fact that animal draught can be essential
for land preparation. Importantly, for the design
of new mixed systems, the amount of digestible
nutrients in straws and stovers can be increased
through treatments, agronomic practices or choice
of cultivar (Sundstøl and Owen, 1984; Singh and
Schiere, 1993; Joshi et al., 1994). Also, the quality
of ley fodder can be influenced, for example, by
the choice between use of legumes or grasses, by
cutting regimes, or by season.
• Careful adjustment of individual animal and plant
subsystem output for maximum total system output
as discussed by Kidane (1984), Schiere and Grasman (1997) and Schiere et al. (1999). Individual
animal output cannot be very high if crop residues
and grasses alone are the sole feed resource. In fact,
output targets that exceed the carrying capacity of
the feed resource base will even result in reduced
total system output (Kater, 1989).
6.2.2. SOM and N balances
A major purpose of including a ley for higher system sustainability is to increase SOM including soil
nitrogen (Theron and Haylett, 1953; Feigin et al.,
1975; Kaasschieter et al., 1990; Bosma et al., 1994;
Bationo et al., 1995). As shown above, inclusion of
a ley implies a trade-off between FOOD PLUS in the
short term and long term, or in terms of this paper:
between FOOD PLUS and SOM. The comparison
between FOOD PLUS and SOM becomes more interesting when considering the choice between a grass
and a legume ley. In principle, a fertilised grass ley
provides more SOM than a legume ley, if only because a legume uses part of the absorbed solar energy
for the fixation of atmospheric nitrogen (Penning de
Vries et al., 1989). The point where net loss/gain
of SOM is zero, is the minimum ley area required
for sustained FOOD PLUS. This point (the intersect
of these lines on X-axis) is indicated in Fig. 4b by
SOMG for grass and SOML for legume leys. If stable
or increased SOM levels are required for sustainable
agriculture, (position of) these points illustrate that
less land needs to be followed, i.e. that more people are likely to be sustained with a fertilised grass
than a legume ley. The negative trade-off of a grass
ley is that nitrogen has to be applied from external
149
sources, contrary to legume leys that are self-sufficient
for nitrogen.
6.2.3. Resistance to shock
A system (Fig. 4) at the left-hand side of the X-axis
with high FOOD PLUS is presumably politically stable in the short term. However, pure cropping systems
produce less than mixed systems if no nitrogen and
SOM are added from outside sources. This implies
less stability in the long term and/or stronger political
dependence, again a case of short versus long term.
Moreover, the use of leys and keeping animals is a
form of diversification that act as a kind of buffer with
likely positive effects on the resilience and stability of
a system (Bosma et al., 1993; Bosman, 1995; Mace
and Houston, 1989; Sansoucy, 1995; Thomas and
Lascano, 1995).
6.2.4. Nutrient cycling
Systems that shift towards NCA in Fig. 3B show
a tendency towards intensive nutrient cycling within
the system. Since all resources tend to cycle within
the system, a disturbance in one of the subsystems
translates into disfunctioning elsewhere. Whereas
HEIA lies in the supply of external resources, NCA
lies in the internal circulation and mutual adjustment.
Indeed, integration of crop–livestock systems for maximum FOOD PLUS in NCA is based on interdependency, i.e. it requires intensive mutual adjustment as
discussed above. This is different in EXPAGR where
livestock and crops are managed rather independently
as a form of risk-spreading and/or economic reasons
through diversification. In EXPAGR, therefore, the
failure of one is compensated by the success of the
other, in the case of NCA, failure of one component
can imply collapse of the system.
The height of the lines AB and A B above the
subsistence requirements of a given population in
Fig. 6 indirectly indicate income in the system. In
that case, it is important to know that the price for
energy and especially protein originating from animal produce can be a factor 5–10 higher than those
from plant sources (Crotty, 1980). Therefore, when
the production of a system is expressed in monitory
terms, it moves to the line A B , illustrating that livestock helps to compensate the losses incurred with a
ley (NRC, 1989), thus positively contributing to food
security in the long term.
150
J.B. Schiere et al. / Agriculture, Ecosystems and Environment 90 (2002) 139–153
6.2.5. Equity
Integration of crops and livestock on-farm can
enhance equity, one of the criteria for sustainability proposed by Conway (1986). It can also affect
the export of plant nutrients to the urban centres
by providing labour opportunity and income for the
country-side, as more added value remains on farm
when crop by-products are fed on farm. Integration of
several forms of production is likely to reduce pollution problems, because waste from one subsystem can
serve as a resource for another subsystem. Thus, the
waste/losses flows can be reduced due to integration
as indicated in Fig. 3B.
7. Conclusions
Changes in resource/demand patterns cause changes
in the behaviour of (livestock) production systems.
This implies that livestock can be essential for the
sustainability of one system in one context and detrimental for the same or another system in a context
elsewhere with other resource flows. It is possible
to identify contexts and systems where livestock can
be useful for increased sustainability and the generalised claims that livestock are detrimental is not supported. Clearly, the complexity of decision making
increases when more factors are involved, i.e. when
more criteria for sustainability are used. It is a form
of experimentation and data handling that is alien to
the traditional approaches in reductionist research that
separates all factors to study only a few at a time.
This paper breaks with such a tradition. The planning
and design of sustainable farm systems is a process
that involves multiple criteria for system success and
sustainability in situations that change over time and
space. Conceptual models discussed allow identification and quantification of important issues, but they
clearly generate as many questions as answers. Depending on conditions in time and space, a decision
can be taken that selects the best (or least destructive)
option.
Reduced access to land leads to modified, if not
lower biomass (=feed) availability. When expansion
of the resource base such as prevalent in the EXPAGR
and HEIA mode of agriculture becomes difficult,
sustained production of FOOD PLUS must originate
from savings in the system or from adjustment of
demand patterns. Proper system design and judicious
use of external inputs can correct imbalances in a
system with appropriate management. Especially,
in pastoral and specialised systems, livestock keeping is associated with environmental degradation,
but livestock creates opportunities for sustainability in mixed systems. When land is the limiting
factor, a major production objective is to maintain
or increase land quality, e.g. by maintaining or increasing SOM levels for assured food production in
the long run, and to increase total production per
unit land.
Acknowledgements
Thanks are particularly due to the students and colleagues Marinus Bos, Loes Kater, Yun Insiani and Gert
Kaasschieter whose work was at the basis of this paper. Thanks are also due to Ton van Schie for his help
in editing and revising several drafts and in preparing
the figures.
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