doi: 10.1111/j.1475-2743.2007.00137.x
Soil Use and Management
Sustainable agricultural development in sub-Saharan
Africa: the case for a paradigm shift in land husbandry
J. W. Gowing & M. Palmer
School of Agriculture, Food and Rural Development, Newcastle University, Newcastle upon Tyne NE1 7RU, UK
Abstract
In order to tackle poverty and hunger in sub-Saharan Africa (SSA) there is a strong case for a focus
of effort on improving rainfed agricultural systems. The challenge is to deliver a transformation of
agricultural productivity in such systems without adverse impacts on environmental goods and services. We examine the growing advocacy of ‘conservation agriculture’ (CA) as the desired approach
and assess the evidence to support the assertion that it can deliver sustainable agricultural development in SSA. We examine in particular the evidence which derives from experience with ‘zero tillage
sustainable agriculture’ in Brazil. We ask the question, is there a case for a paradigm shift in land husbandry? The case for a paradigm shift hangs on the premise that conventional practice promotes land
degradation, while adoption of CA practice delivers a range of benefits through promoting soil ecosystem health. The guiding principle is to promote biological tillage through minimizing mechanical soil
disturbance and maintaining permanent organic soil cover. We examine evidence of benefits in the
context of the wider debate on low-external-input technology. We conclude that CA does not overcome constraints on low-external-input systems and will deliver the productivity gains that are
required to achieve food security and poverty targets only if farmers have access to fertilizers and herbicides. We conclude also that widespread adoption of the new paradigm amongst millions of small
farmers in order to achieve the ‘doubly green revolution’ in SSA is subject to the familiar constraints
of knowledge transfer and success will depend upon creating innovation networks. Further, we conclude that amongst small-scale farmers partial adoption will be the norm and it is not clear that this
will deliver soil health benefits claimed for full adoption of the new paradigm.
Keywords: Africa, conservation agriculture, land husbandry, sustainable development
Introduction
Fifty years ago there were fewer than half as many people as
there are today. They were not as wealthy and the pressure
they inflicted on the environment was lower. The widely held
view then was that global development would necessarily
involve increased exploitation of environmental resources, in
particular, land and water. Since then population growth
and dietary change have driven up demand for food and
other agricultural products and in the next 50 years, global
food and feed crop demand is expected to double. The consensus view has changed; now there is greater recognition of
conflict between development and environmental protection
objectives and many commentators are asking: is there
Correspondence: J. W. Gowing. E-mail: [email protected]
Received July 2007; accepted after revision September 2007
enough land and water to deliver food security and sustainable development over the next 50 years? (Greenland et al.,
1998; Rosegrant et al., 2002; Brown, 2004; CAWMA, 2007).
Choices about management of land and water resources
will determine to a large extent whether we reach the interlinked multiple objectives of economic and social development as articulated in the Millennium Development Goals
(MDGs).1 The challenge to the world community on poverty
and hunger in particular is encapsulated in two ambitious
targets:
1
Goal 1, eradicate extreme poverty and hunger; Goal 2, achieve universal primary education; Goal 3, promote gender equality and
empower women; Goal 4, reduce child mortality; Goal 5, improve
maternal health; Goal 6, combat HIV ⁄ AIDS, malaria and other diseases; Goal 7, ensure environmental sustainability; Goal 8, develop a
global partnership for development.
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J. W. Gowing & M. Palmer
• To halve between 1990 and 2015, the proportion of people
whose income is less than one dollar a day.
• To halve between 1990 and 2015, the proportion of people
who suffer from hunger.
Recent analysis by the World Bank and ILO has shown
that relative to other economic sectors, increasing agricultural productivity offers the best prospect of tackling poverty
and hunger (Majid, 2004; Rosegrant et al., 2007). In order to
achieve the MDGs there is a strong case for a focus of effort
on improving productivity of low yield rainfed agricultural
systems (CAWMA, 2007). The challenge therefore is to
develop technologies and practices that deliver improved
agricultural productivity in such systems without adverse
impacts on environmental goods and services.
The Green Revolution brought substantial productivity
increases over the last quarter of the 20th century through
developing and promoting packages of external inputs
(seed + fertilizer + pesticide). It has been argued that a second transformation of agriculture is now required that is
‘doubly green’ (Conway, 1997) in that it should both protect
the environment and boost output. The discussion presented
here should be seen in the context of this debate with a particular focus on land husbandry.
A general critique of the notion of a doubly green revolution (Blackman, 2000) identified obstacles to the desired
transformation which will entail convincing millions of
farmers to adopt new practices. These obstacles include a
policy environment which favours input-intensive agriculture
and the fact that alternative environmentally friendly technologies involve high set-up costs. Set against this gloomy
prognosis, there is a body of empirical evidence which suggests that widespread adoption and innovation of alternative sustainable technologies can and does occur. We will
examine in particular the evidence which derives from experience with ‘zero tillage (ZT) sustainable agriculture’ in
Brazil.
The target for our discussion will be sub-Saharan Africa
(SSA) where essentially the same system is being actively
promoted by FAO as ‘conservation agriculture’ (International Institute for Rural Reconstruction & African Conservation Tillage Network, 2005). We focus on SSA because it
was largely untouched by the original Green Revolution
and is lagging behind other regions in progress towards
achieving the MDGs. At the midway point between their
adoption in 2000 and the 2015 target date SSA is not on
track to achieve any of the MDGs (United Nations, 2007).
The number of extremely poor people has levelled off, but
does not show significant decline. The number of food insecure people continues to rise. Faced with high population
growth, in order to achieve food security, the current rate
of increase in food production must be doubled. These are
very substantial challenges and we need to consider the
compatibility of short- to medium-term aims with a longterm sustainability agenda.
What is conservation agriculture?
Conservation agriculture (CA) is described by FAO (http://
www.fao.org/ag/ca) as a concept for resource-saving agricultural crop production which is based on enhancing natural
biological processes above and below ground. CA is characterized by:
• Minimum mechanical soil disturbance
• Permanent organic soil cover
• Diversified crop rotations
This represents a new paradigm in land husbandry which
embraces but is not limited to adoption of conservation tillage. CA aims to maintain a permanent or semi-permanent
organic soil cover which can be either a growing crop or
dead mulch. Its function is to protect the soil physically from
sun, rain and wind and to provide a substrate for the soil
biota. Mechanical tillage incorporates and buries biomass
and at the same time disturbs the natural soil biological processes. Therefore, minimum tillage and direct seeding are
important elements of the concept which derives from experience in Brazil with so-called ‘ZT sustainable agriculture’.
Zero tillage is an important component of CA but farmers
who have adopted ZT are not necessarily practising CA.
Conservation tillage embraces ZT within a wider set of practices that aim to leave crop residues on the surface. Thus ZT
is related to and may be a transition step towards CA, but it
is not the same thing. Direct seeding involves seeding ⁄ planting without preparing a seedbed and is also an important
component of CA, but the term also applies to the use of
mechanical implements which combine primary and secondary tillage with seeding in a single operation. Finally, it
should be noted that CA is not the same as organic farming
(ecological agriculture) although both aim to promote natural soil processes. An important difference is that CA does
not preclude the use of chemical inputs, in particular fertilizers and herbicides, but they are not allowed in organic
systems.
The global extent of CA is reviewed by Derpsch (2005).
There has been widespread adoption in large-scale mechanized farming systems in drylands of the United States and
Australia, but for our context the most notable success story
for CA is its widespread adoption in Brazil. Bolliger et al.
(2006) in a comprehensive review of what they describe as
the ‘zero-till revolution’ report that the system has spread
from less than 1000 ha in 1973 ⁄ 4 to cover 22 million ha by
2003 ⁄ 4 and now represents 45% of the total cultivated area
in Brazil. There is also evidence of CA adoption among
small-scale farmers in the rice–wheat farming system of the
Indo-Gangetic plains in Asia (Hobbs & Gupta, 2002). Lal
(2007) concludes that adoption is practically nil amongst
resource-poor small-scale farmers in SSA, but there is evidence of pockets of adoption; Ekboir et al. (2002) reported
100 000 adopters in Ghana, and Baudron (2005) reported a
10% adoption rate amongst smallholders in Zambia.
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The case for a paradigm shift in land husbandry 3
Why does CA represent a new paradigm?
Conservation agriculture represents a significantly different
approach to land husbandry because it involves adoption of
biological tillage principles. Conventional agriculture involves
mechanical tillage which aims to incorporate crop residues,
control weeds, alleviate soil compaction and prepare a seedbed. However, this often has detrimental effects on the soil
leading to loss of soil organic matter (SOM), reduced fertility, reduced rainfall infiltration and increased erosion. Conservation tillage practices were developed to target in
particular the issue of erosion, through reducing tillage effort
and retaining at least 30% soil cover by mulching with crop
residues. This in itself involves a change of practice on the
part of the farmer, but adoption of CA requires a more radical shift in thinking – a new paradigm.
Conservation agriculture starts from the principle that soil
disturbance through mechanical tillage including hand
power, animal power and tractor power is detrimental. Soil
degradation is seen as a problem characterized by loss of
organic matter content and soil biota, collapse of porosity,
soil capping and compaction. Porous and well-structured soil
conditions are seen as critical to maximizing crop productivity (Shaxson & Barber, 2003). Loss of soil porosity results in
(i) unacceptable run-off of rainwater leading to early onset
of drought and accelerated erosion, (ii) hindrances to optimum functioning of plant roots and (iii) restrictions to effective functioning of soil biota in nutrient cycling. The primary
cause is regarded as mechanical tillage. The guiding principle
therefore is to minimize soil disturbance and to rely on biological tillage within a healthy soil ecosystem.
Soil life plays a major role in many natural processes that
determine nutrient and water availability for agricultural
productivity. A healthy soil ecosystem (Bot & Benites, 2001,
2005) will:
• Decompose organic matter into humus;
• Retain nitrogen and other plant nutrients;
• Increase soil aggregate stability;
• Increase soil porosity;
• Protect roots from diseases and parasites;
• Make available nutrients to the plant;
• Produce hormones that help plants grow.
The living part of SOM includes a wide variety of microorganisms such as bacteria, viruses, fungi, protozoa and
algae. It also includes plant roots, insects and earthworms.
Micro-organisms, earthworms and insects help break down
crop residues and manures by ingesting them and mixing
them with the minerals in the soil, and in the process recycling energy and plant nutrients. Plant roots, fungal hyphae
and sticky exudates from earthworms and micro-organisms
bind soil particles into water-stable aggregates, reducing erosion and increasing porosity (Tisdall & Oades, 1982). Shallow-dwelling earthworms create numerous channels
throughout the topsoil, which increases overall porosity,
while large vertical channels created by deep-burrowing
earthworms improve soil structure in subsoil. The required
shift in thinking therefore is to manage land in a way that
promotes soil ecosystem health.
What is the evidence-base for promoting CA?
The direct benefits of CA adoption in Brazil are said to
include sustainable high yield levels, reduced soil erosion and
reduced costs (lower net inputs of fertilizer, fuel and labour).
They are widely reported and provide a reasonable explanation of widespread adoption, but it has been hard to find evidence to substantiate them in accessible peer-reviewed
literature. However, Bolliger et al. (2006) recently published
a detailed review of the evidence accumulated over several
decades on CA innovation in Brazil.
Empirical evidence of the benefits of CA from SSA is limited. Lal (1998) reports long-term trials in Nigeria with ZT
rather than CA systems, although these were research station
experiments rather than on-farm trials. He found that ZT
slightly outperformed conventional tillage in most seasons,
but soil chemical and physical quality declined under continuous maize cultivation regardless of the tillage system. Rockstrom et al. (2007) reports CA trials in Ethiopia, Kenya,
Tanzania and Zimbabwe that have generated yield improvements in the range of 20–120% in smallholder rainfed agriculture. However, it should be noted that the so-called CA
systems adopted in these trials failed to maintain permanent
organic soil cover (J. Rockstrom, personal communication)
and also included limited use of chemical fertilizer.
In the case of rice–wheat systems in South Asia, Hobbs
(2007) provides a better substantiated range of benefits,
which include reduced production costs (fuel and labour),
increased yield and reduced pest and disease problems. He
reports that CA leads to significantly improved physical and
chemical properties of soil and that biotic diversity in the soil
is increased. This supports the argument that CA creates a
more healthy soil and enables more efficient use of natural
resources.
Documented evidence on the issue of soil health is more
widely available (though not from SSA). CA practices have
been shown to produce higher surface SOM content (Roldan
et al., 2003; Alvear et al., 2005; Diekow et al., 2005; Madari
et al., 2005). Bolliger et al. (2006) report average-enhanced
SOM accumulation rates of 0.4–1.7 t ha)1 year)1 under ZT
systems in comparison with conventional tillage. Increased
ground cover is associated with an increase in biodiversity
both above ground and in the soil (Kendall et al., 1995; Jaipal et al., 2002). Reduced tillage has been shown to increase
soil fauna (Karlen et al., 1994; Buckerfield & Webster, 1996;
Clapperton, 2003; Birkas et al., 2004; Rodriguez et al., 2006).
However, there is also evidence that these effects may be
exaggerated by increased stratification in low ⁄ no till systems.
Peigne et al. (2007) reports that conservation tillage leads to
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J. W. Gowing & M. Palmer
increased soil organic carbon (SOC) at 0–5 cm depth but
there is no significant increase in the overall mass of SOC or
soil microbial biomass in the whole topsoil layer (0–30 cm).
There is still some controversy as to the true effects of ZT
on SOC, and in particular claims about carbon sequestration
potential. Farage et al. (2007) modelled dryland farming systems in Nigeria and Sudan and showed rates of carbon
sequestration in the range 0.08–0.17 t ha)1 year)1. However,
this depends upon the input of organic matter, which is
acknowledged to be a serious constraint in SSA because of
competing demands on crop residues as fodder and animal
manure as fuel (Lal, 2004). Ball et al. (1998) concluded that
additional carbon fixation by storage of SOM and oxidation
of atmospheric methane was very limited under reduced tillage and likely to be only a short-term effect. Problems of
reporting arise firstly due to increased SOM stratification
under ZT, and failure to take sufficient notice of differences
in depth distribution with tilled systems. Secondly, it is difficult to separate the effects of reduced tillage from those of
increased biomass production and retention under ZT systems, and hence the desirability of ZT as opposed to increasing productivity of conventional systems through fertilizer
use increase and greater biomass return is difficult to evaluate. Ringius (2002) considers the opportunities and challenges for soil carbon sequestration in Africa and points out
that under the Clean Development Mechanism of the Kyoto
protocol, forest planting would be eligible for credit and
therefore attract investment from foreign governments
towards their own emission reduction obligation, but soil
carbon sequestration was not included in the scheme. For
SOC restoration to be considered as a carbon sink and hence
attract investment in a similar way to forest management,
further research is required to assess the genuine potential
and cost justification.
Does Brazilian experience of CA represent a case
for adopting the new paradigm in SSA?
To answer this question, we can examine CA in the context
of the wider debate on ‘low-external-input technology
(LEIT)’ (Tripp, 2006) or ‘resource-conserving agriculture’
(Pretty et al., 2006). The test is that adoption of the new paradigm in SSA should deliver poverty alleviation and food
security benefits.
So-called ‘bright spots’ are examples of interventions
which have successfully reversed the continuing downward
spiral of poverty, and which reveal positive impacts on land
and water resources. Pretty et al. (2006) gathered evidence
from 286 ‘bright spots’ in 57 poor countries. These projects
made use of a variety of packages of resource-conserving
technologies and practices, including:
• Integrated nutrient management
• Conservation tillage
• Agroforestry
• Water harvesting
• Livestock integration
• Integrated pest management
This was a purposive sample of ‘best practice’ which found
that the mean relative yield increase was 79% across a very
wide range of crops and systems. For the farm system categories most relevant to our discussion (smallholder rainfed
humid, smallholder rainfed highland, smallholder rainfed
dry ⁄ cold) and for maize, millet, sorghum, potatoes and
legumes across all systems, mean yield increase exceeded
100%. But will this be enough? CA is being promoted for
small-scale semi-subsistence farmers in SSA as a resourceconserving practice, but the evidence suggests that food security benefits are open to doubt. Pretty et al. (2006) conclude
that it is uncertain whether progress is sufficient to meet
future food needs in view of continued population growth,
urbanization and dietary transition to meat-rich diets.
A review of the research conducted in recent years on
LEITs by Graves et al. (2004) is also revealing in that it
raises doubts about their sustainability. They ask the question, ‘can low-external-input agriculture meet future food
security needs while protecting the environment’? They echo
the concern about the potential productivity of such systems
in which the constraint is shown to be maintenance of soil
fertility and SOM. In any low-input system, the alternative
to mineral fertilizer is ‘biomass transfer’ in the form of animal manure, or direct input of cut plant material (which
may be composted). The system, in effect, involves ‘nutrient
mining’ from the soil where the biomass is produced. The
quantity of biomass available to small farmers is commonly
insufficient because of limited land and ⁄ or limited labour.
They conclude that low-external-input technologies appear to
have limited potential to increase food production for the
target group of resource-poor farmers. We are not aware
that any evidence has been presented which shows that this
constraint in low-input systems can be overcome by adoption
of CA principles.
Turning to the poverty-alleviation objective, a recent analysis of low-input technological interventions, by Tripp (2006)
paints a negative picture of progress made, and questions
some of the claims made about their potential. He concludes
that, contrary to the belief that low-input techniques have
greatest benefit for resource-poor farmers, patterns of uptake
do not differ significantly from Green Revolution technology; it is generally the farmers who are better resourced with
access to markets who invest in any new technology. The
‘small farmers’ reported to have adopted CA in Brazil are
very different from their counterparts in SSA. Smallholders
in Brazil are defined as those farming up to 50 ha (Bolliger
et al., 2006) and land husbandry operations are largely
mechanized, often with animal power. Tripp (2006) also disputes the idea that there is evidence for spontaneous farmerto-farmer diffusion of technology, often seen as integral to
the ultimate success of participatory agro-ecological research
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The case for a paradigm shift in land husbandry 5
methods, arguing that a much more clear definition of
exactly what is needed (in terms of policy, replication, extension, new organizations, etc.) than a general reference to
‘scaling up’ is required to achieve success on a meaningful
scale. This issue is examined further considering the evidence
from Brazil below.
Can Brazilian experience of CA promotion be
replicated in SSA?
We can again learn from the evaluation of evidence from
‘bright spots’. Noble et al. (2006) examined whether there
are key factors that are fundamental to success, and whether
these can be developed into guidelines that would enhance
up-scaling and increase food security and household incomes.
Through a consultative process 10 possible drivers were identified:
Individually based Drivers: Leadership, aspiration for
change.
Socially based Drivers: Social capital, participatory
approach.
Technically based Drivers: Innovation and appropriate
technologies, quick and tangible benefits, low risk of failure.
Externally based Drivers: Supportive policy, property
rights, market opportunities.
Penning de Vries (2005) examined community-based
‘bright spots’ in African agriculture, but it is individual-based
‘bright spots’ that are most relevant to our discussion of land
husbandry interventions. For these the key factors influencing adoption were found to be:
• quick and tangible outcomes
• a participatory approach in implementing the technology
• strong leadership by the individual or group adopting the
technology
• supportive policy
• markets
With the exception of the reference to ‘markets’, which is
becoming common in the discourse on agricultural development in SSA, there is a remarkable similarity to the list
developed by Hudson (1991) in his assessment of the reasons
for adoption or non-adoption of soil conservation practices.
There are cases of what could be termed spontaneously
driven ‘bright spots’ that grew from within, without incentives or external support. However, in the majority of cases
the development of the documented ‘bright spot’ was contingent on an external priming agent which facilitated progress
through financial and non-financial contributions. We must
examine the implications of this evidence for future expansion and up-scaling of knowledge-intensive innovations that
characterize CA.
Ekboir (2003) cites the importance of ‘innovation networks’ to the spread of CA in Brazil, and particularly highlights the importance of agrochemical companies as agents
with sufficient coverage and resources to promote developed
technologies. This, he argues, is the key difference between
its widespread adoption in Brazil and its minimal success in
other countries. Evidence of adoption in SSA, e.g. in Ghana
and Zambia, appears to confirm the importance of such support networks. Ekboir et al. (2002) in their study of CA
adoption in Ghana identified the active markets for agricultural services and the important role of agrochemical dealers.
Baudron (2005), in his study of CA adoption in Zambia,
emphasizes the importance of making input packages available to farmers.
Conclusion
The case for a paradigm shift in land husbandry hangs on
the premise that conventional practice promotes land degradation while adoption of CA practice delivers a range of
benefits through promoting soil ecosystem health. Does it
therefore deliver the doubly green revolution that will lead to
sustainable agricultural development in SSA?
Accumulated evidence shows that if the conditions are
right then CA does deliver benefits sufficient to promote its
adoption amongst farmers. Substantiated benefits include
reduced production costs, improved soil conditions and
reduced erosion. There has been widespread adoption in
large-scale mechanized farming systems in drylands of the
United States and Australia, but more relevant to our discussion is the evidence which derives from experience with ‘ZT
sustainable agriculture’ in Brazil.
We have examined CA in the context of the wider debate
on LEIT. We have examined the subsidiary propositions
that:
• conservation agriculture can deliver the productivity gains
that are required to achieve the MDG food security target
and that advocacy of CA is compatible with the MDG
poverty target;
• widespread adoption of the new paradigm amongst millions of small farmers in order to achieve the ‘doubly green
revolution’ in SSA is achievable.
In considering the first proposition, the available evidence
suggests that LEITs can deliver yield improvements in the
range of 20–120% in smallholder rainfed agriculture compared with ‘unimproved’ traditional systems. At the optimistic end of this range, this will deliver doubling of production
compared with the baseline, which equates to a growth rate
of 3% per annum over 25 years. This is an improvement
over past agricultural growth performance in SSA, but is not
sufficient to achieve the MDG food security target. Lowexternal-input techniques, in general, have limited potential
to deliver a sustainable increase in food production for the
target group of resource-poor farmers. Such systems depend
upon importing biomass to maintain fertility and, in effect,
involve ‘nutrient mining’ from the soil where the biomass is
produced but the quantity of biomass available to small
farmers is insufficient because of limited land and ⁄ or labour.
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J. W. Gowing & M. Palmer
We see no evidence that CA systems overcome these constraints without external inputs.
In considering the second proposition, which concerns
dissemination, there is no evidence that the pattern of uptake
of LEITs differs significantly from Green Revolution technology. There are cases of what could be termed as spontaneously driven ‘bright spots’ that occurred, without incentives
or external support; however, in the majority of cases the
development of the documented ‘bright spot’ was contingent
on an external priming agent, which facilitated progress
through financial and non-financial contributions. We see no
evidence that CA systems are different in this respect. It is
clear that the key to the widespread adoption of CA in Brazil
has been the success of ‘innovation networks’ and in particular the presence of agrochemical companies as agents with
sufficient coverage and resources to promote developed technologies. Where pockets of CA adoption exist in SSA, most
notably in Ghana and Zambia, the same condition applies.
There is a very limited evidence base in SSA, with documented evidence of the benefits of a paradigm shift coming
mainly from Brazil. Small farmers who have adopted CA in
Brazil appear much better resourced than the target group in
SSA. Most importantly they generally have good access to
markets for inputs and outputs. Nevertheless, it should be
noted that the ‘model’ systems developed by agricultural scientists in Brazil have not proved suited to the circumstances
of small farmers and farmers have frequently adapted technologies to suit their capabilities. Assessing the impacts of
these ‘imperfect’ systems may well prove the key to sustainable intensification of smallholder agriculture in SSA.
A particularly contentious issue has been the reliance on
herbicides, which represent 11–12% of smallholder production costs on CA land as opposed to 2–5% under conventional systems. A 17% increase in smallholder herbicide use
is observed with ZT systems in Brazil compared with conventionally cultivated land (Bolliger et al., 2006). It is apparent
that many small-scale farmers in Brazil struggle with weed
control when their access to herbicides is limited and they
often resort to tillage as a solution. The concern about weed
control is echoed by Rockstrom et al. (2007) who suggests
that for resource-poor farm households in SSA the use of
herbicides is not an option. He speculates that the weed
problem ‘will fall below that of the original farming system
after several years’, but evidence from Brazil does not support this optimism. Further confirmation of the critical nature of the weed control problem can be obtained from
Peigne et al. (2007) who conclude that in organic farming
systems (i.e. without use of herbicides) ZT tends to increase
weed pressure to a critical level where crop production could
be compromised.
The concern extends beyond the question of weed control
to embrace also the issue of fertilizers. The problem of
securing sufficient biomass for soil cover and for sustaining
adequate fertility will remain a key issue in SSA. The use
of mineral fertilizers, assuming they are available, would be
compatible with a CA system and evidence suggests a pragmatic approach may be appropriate. A third important
proposition therefore needs to be properly tested in examining the case for adopting a new paradigm for land husbandry. Given that partial adoption of CA principles
appears to be the norm amongst small-scale, resource-poor
farmers, does it deliver comparable soil health benefits?
What level of mechanical tillage for weed control is permissible? What level of mineral fertilizer input is acceptable?
We agree with the conclusion of Bolliger et al. (2006) that
perhaps the real lessons are to be learnt from the adaptations made by farmers.
Acknowledgements
This paper is based on a presentation made by the authors
at an International Workshop on Land Husbandry which
was convened by the Tropical Agriculture Association and
hosted by University of Newcastle upon Tyne in March
2007. We have benefited from that discussion but the opinions expressed here are our own.
References
Alvear, M., Rosas, A., Rouanet, J.L. & Borie, F. 2005. Effects of
three soil tillage systems on some biological activities in an Ultisol
from southern Chile. Soil & Tillage Research, 82, 195–202.
Ball, B.C., Tebrugge, F., Sartori, L., Giraldez, J.V. & Gonzalez, P.
1998. Influence of no-tillage on physical, chemical and biological
soil properties. In: Experiences with the applicability of no-tillage
crop production in the west-European countries (eds F. Tebrugge &
A. Bohrnsen), pp. 7–27. Justus-Liebig University, Giessen,
Germany.
Baudron, F. 2005. Challenges for the adoption of conservation agriculture by smallholders in semi-arid Zambia. In: Proceedings Third
World Congress on Conservation Agriculture, Nairobi, Kenya.
Available at: http://www.act.org.zw.
Birkas, M., Jolankai, M., Gyuricza, C. & Percze, A. 2004. Tillage
effects on compaction, earthworms and other soil quality indicators in Hungary. Soil & Tillage Research, 78, 185–196.
Blackman, A. 2000. Obstacles to a doubly green revolution. Discussion Paper 00-48. Resources for the Future, Washington DC. Available at: http://www.rff.org/rff/Publications/Discussion_Papers.cfm
(accessed online 16 July 2007).
Bolliger, A., Magid, J., Amado, T.J.C., Skora Neto, F., Ribeiro,
M.F.S., Calegari, A., Ralish, R. & Neergaard, A. 2006. Taking
stock of the Brazilian ‘‘zero-till revolution’’: a review of landmark
research and farmers’ practice. Advances in Agronomy, 91, 47–110.
Bot, A. & Benites, J. 2001. Conservation agriculture: case studies in
Latin America and Africa. FAO Soils Bulletin 78. FAO, Rome.
Bot, A. & Benites, J. 2005. The importance of soil organic matter.
FAO Soils Bulletin 80. FAO, Rome.
Brown, L. 2004. Outgrowing the Earth: the food security challenge in
an age of falling water table and rising temperatures. Earth Policy
Institute, London & W.W. Norton & Company, New York.
ª 2007 The Authors. Journal compilation ª 2007 British Society of Soil Science, Soil Use and Management
The case for a paradigm shift in land husbandry 7
Buckerfield, J.C. & Webster, K.A. 1996. Earthworms, mulching, soil
moisture and grape yields: earthworms responses to soil management practices in vineyards, Barossa Valley, South Australia. Australia and New Zealand Wine Industry Journal, 11, 47–53.
CAWMA 2007. Water for food, water for life: a comprehensive
assessment of water management in agriculture. Earthscan, London.
Clapperton, M.J. 2003. Increasing soil biodiversity through habitat
conservation agriculture: managing the soil as a habitat. In: Producing in harmony with nature: Proceedings of the Second World
Congress on Conservation Agriculture, Iguassu Falls, Parana, Brazil, August 2003. FAO (CD), Rome.
Conway, G. 1997. The doubly green revolution. Penguin Books, London.
Derpsch, R. 2005. The extent of conservation agriculture adoption
worldwide: implications and impact. Keynote paper at third world
congress on conservation agriculture. World Agroforestry Centre,
Nairobi.
Diekow, J., Mielniczuk, J., Knicker, H., Bayer, C., Dick, D.P. &
Kogel-Knaber, I. 2005. Soil C and N stocks as affected by cropping systems and nitrogen fertilization in a southern Brazil Acrisol
managed under no-tillage for 17 years. Soil & Tillage Research, 81,
87–95.
Ekboir, J.M. 2003. Research and technology policies in innovation
systems: zero tillage in Brazil. Research Policy, 32, 573–586.
Ekboir, J.M., Boa, K. & Dankyi, A.A. 2002. Impacts of no-till technology in Ghana. CIMMYT Research Report. CIMMYT, Mexico.
Farage, P.K., Ardö, J., Olsson, L., Rienzi, E.A., Ball, A.S. & Pretty,
J.N. 2007. The potential for soil carbon sequestration in three
tropical dryland farming systems of Africa and Latin America: a
modelling approach. Soil & Tillage Research, 94, 457–472.
Graves, A., Matthews, R. & Waldie, K. 2004. Low external input
technologies for livelihood improvement in subsistence agriculture.
Advances in Agronomy, 82, 473–555.
Greenland, D.J., Gregory, P.J. & Nye, P.H. 1998. Land resources;
on the edge of the Malthusian precipice. Philosophical Transactions
of the Royal Society of London. Series B, 352, 861–867.
Hobbs, P.R. 2007. Conservation agriculture; what is it and why is it
important for future sustainable food production? Journal of Agricultural Science, 145, 127–137.
Hobbs, P.R. & Gupta, R.K. 2002. Rice–wheat cropping systems in
the Indo-Gangetic plains: issues of water productivity in relation
to new resource conserving technologies. In: Water productivity
in agriculture: limits and opportunities for improvement (ed. J.W.
Kijne), pp. 239–253. CABI Publishing, Wallingford, UK.
Hudson, N.W. 1991. A study of the reasons for success or failure of
soil conservation projects. FAO Soils Bulletin 64. FAO, Rome.
International Institute for Rural Reconstruction & African Conservation Tillage Network 2005. Conservation agriculture: a manual
for farmers and extension workers. IIRR & Harare: ACT, Nairobi.
Jaipal, S., Singh, S., Yadav, A., Malik, R.K. & Hobbs, P.R. 2002.
Species diversity and population density of macro-fauna of rice–
wheat cropping habitat in semi-arid subtropical northwest India in
relation to modified tillage practices of wheat sowing. In: Herbicide resistance management and zero-tillage in the rice wheat cropping system (eds R.K. Malik, R.S. Balyan, A. Yadav & S.K.
Pathwa) Proceedings of an International Workshop, Hissar, India,
March 2002, pp. 166–171. CCS Haryana University, Hissar, India.
Karlen, D.L., Wollenhaupt, N.C., Erbach, D.C., Berry, E.C., Swan,
J.B., Eash, N.S. & Jordah, J.L. 1994. Crop residue effects on soil
quality following 10 years of no-till corn. Soil & Tillage Research,
31, 149–167.
Kendall, D.A., Chin, N.E., Glen, D.M., Wiltshire, C.W., Winstone,
L. & Tidboald, C. 1995. Effects of soil management on cereal
pests and their natural enemies. In: Ecology and integrated farming
systems, Proceedings of the 13th Long Ashton International Symposium, Chichester, UK (eds D.M. Glen, M.P. Greaves & H.M.
Anderson), pp. 83–102. Wiley Press, New York.
Lal, R. 1998. Soil quality changes under continuous cropping for
seventeen seasons of an alfisol in western Nigeria. Land Degradation & Development, 9, 259–274.
Lal, R. 2004. Soil carbon sequestration to mitigate climate change.
Geoderma, 123, 1–22.
Lal, R. 2007. Constraints to adopting no-till farming in developing
countries. Soil & Tillage Research, 94, 1–3.
Madari, B., Machado, P.L.O.A., Torres, E., De Andrade, A.G. &
Valencia, L.I.O. 2005. No tillage and crop rotation effects on soil
aggregation and organic carbon in a Rhodic Ferralsol from southern Brazil. Soil & Tillage Research, 80, 185–200.
Majid, N. 2004. Reaching millenium goals: how well does agricultural
productivity growth reduce poverty? Employment Strategy Papers,
International Labour Organisation, Geneva. Available at: http://
www.ilo.org/public/english/employment/strat/download/esp12.pdf
(accessed online 16 July 2007).
Noble, A.D., Bossio, D., Dixon, J., Hine, R.E., Penning de Vries,
F.W.T., Pretty, J. & Thiyagarajan, T.M. 2006. Intensifying agricultural sustainability: an analysis of impacts and drivers in the development of bright spots. Comprehensive Assessment Research
Report 13. IWMI 2006. Colombo, Sri Lanka. Available at: http://
www.iwmi.cgiar.org/Assessment/Publications/research_reports.htm
(accessed online 23 March 2007).
Peigne, J., Ball, B.C., Roger-Estrade, J. & David, C. 2007. Is conservation tillage suitable for organic farming? A review. Soil Use and
Management, 23, 129–144.
Penning de Vries, F.W.T. (ed.) 2005. Bright spots demonstrate community successes in African agriculture. Working Paper 102. International Water Management Institute, Colombo, Sri Lanka.
Pretty, J., Noble, A.D., Bossio, D., Dixon, J., Hine, R.E., Penning
de Vries, F.W.T. & Morrison, J.I.L. 2006. Resource conserving
agriculture increases yields in developing countries. Environmental
Science and Technology, 40, 1114–1119.
Ringius, L. 2002. Soil carbon sequestration and the CDM: opportunities and challenges for Africa. Climatic Change, 54, 471–495.
Rockstrom, J., Hatibu, N., Oweis, T.Y., Wani, S., Barron, J., Bruggeman, A., Farahani, J., Karlberg, L. & Qiang, Z. 2007. Managing
water in rainfed agriculture. In: CAWMA (2007) Water for food,
water for life: a comprehensive assessment of water management in
agriculture (Chapter 8). Earthscan, London.
Rodriguez, E., Fernadez-Anero, F.J., Ruiz, P. & Campos, M. 2006.
Soil arthropod abundance under conventional and no-tillage in a
Mediterranean climate. Soil & Tillage Research, 80, 79–93.
Roldan, A., Caravaca, F., Hernandez, M.T., Garcia, C., SanchezBrito, C., Velasquez, M. & Tiscareno, M. 2003. No-tillage, crop
residue additions, legume cover cropping effects on soil quality
characteristics under maize in Patzcuaro watershed (Mexico). Soil
& Tillage Research, 72, 65–73.
ª 2007 The Authors. Journal compilation ª 2007 British Society of Soil Science, Soil Use and Management
8
J. W. Gowing & M. Palmer
Rosegrant, M.W., Cai, X. & Cline, S.A. 2002. World water and food
to 2025: dealing with scarcity. International Food Policy Institute,
Washington DC.
Rosegrant, M.W., Ringler, C., Benson, T., Diao, X., Resnick, D.,
Thurlow, J., Toreror, M. & Orden, D. 2007. Agriculture and achieving the millenium development goals. World Bank (Agriculture &
Rural Development Department), New York. Available at: http://
www.ifpri.org/pubs/cp/agmdg.asp (accessed online 16 July 2007).
Shaxson, F. & Barber, R. 2003. Optimising soil moisture for plant
production. FAO Soils Bulletin 79. FAO, Rome.
Tisdall, J.M. & Oades, J.M. 1982. Organic-matter and waterstable aggregates in soils. Journal of Soil Science, 33, 141–
163.
Tripp, R. 2006. Is low external input technology contributing to sustainable agricultural development? Natural Resources Perspectives
No. 102. ODI, London.
United Nations 2007. Africa and the millennium development goals.
Available at: http://www.un.og/millenniumgoals (accessed online
16 July 2007).
ª 2007 The Authors. Journal compilation ª 2007 British Society of Soil Science, Soil Use and Management