SOIL, 1, 491–508, 2015
www.soil-journal.net/1/491/2015/
doi:10.5194/soil-1-491-2015
© Author(s) 2015. CC Attribution 3.0 License.
SOIL
Integrated soil fertility management in sub-Saharan
Africa: unravelling local adaptation
B. Vanlauwe1, K. Descheemaeker2, K. E. Giller2, J. Huising3, R. Merckx4, G. Nziguheba1, J. Wendt5,
and S. Zingore6
1International Institute of Tropical Agriculture (IITA), Nairobi, Kenya
2Plant Production Systems, Wageningen University, P.O. Box 430, Wageningen, the Netherlands
3International Institute of Tropical Agriculture (IITA), Ibadan, Nigeria
4Department of Earth and Environmental Sciences, Katholieke Universiteit Leuven (KU Leuven),
Leuven, Belgium
5International Fertilizer Development Cooperation (IFDC), Nairobi, Kenya
6International Plant Nutrition Institute (IPNI), Nairobi, Kenya
Correspondence to: B. Vanlauwe (b.vanlauwe@cgiar.org)
Received: 27 September 2014 – Published in SOIL Discuss.: 20 December 2014
Revised: 06 April 2015 – Accepted: 06 May 2015 – Published: 22 June 2015
Abstract. Intensification of smallholder agriculture in sub-Saharan Africa is necessary to address rural poverty
and natural resource degradation. Integrated soil fertility management (ISFM) is a means to enhance crop pro-
ductivity while maximizing the agronomic efficiency (AE) of applied inputs, and can thus contribute to sus-
tainable intensification. ISFM consists of a set of best practices, preferably used in combination, including the
use of appropriate germplasm, the appropriate use of fertilizer and of organic resources, and good agronomic
practices. The large variability in soil fertility conditions within smallholder farms is also recognized within
ISFM, including soils with constraints beyond those addressed by fertilizer and organic inputs. The variable
biophysical environments that characterize smallholder farming systems have profound effects on crop produc-
tivity and AE, and targeted application of agro-inputs and management practices is necessary to enhance AE.
Further, management decisions depend on the farmer’s resource endowments and production objectives. In this
paper we discuss the “local adaptation” component of ISFM and how this can be conceptualized within an ISFM
framework, backstopped by analysis of AE at plot and farm level. At plot level, a set of four constraints to maxi-
mum AE is discussed in relation to “local adaptation”: soil acidity, secondary nutrient and micronutrient (SMN)
deficiencies, physical constraints, and drought stress. In each of these cases, examples are presented whereby
amendments and/or practices addressing these have a significantly positive impact on fertilizer AE, including
mechanistic principles underlying these effects. While the impact of such amendments and/or practices is easily
understood for some practices (e.g. the application of SMNs where these are limiting), for others, more com-
plex processes influence AE (e.g. water harvesting under varying rainfall conditions). At farm scale, adjusting
fertilizer applications to within-farm soil fertility gradients has the potential to increase AE compared with blan-
ket recommendations, in particular where fertility gradients are strong. In the final section, “local adaption” is
discussed in relation to scale issues and decision support tools are evaluated as a means to create a better under-
standing of complexity at farm level and to communicate appropriate scenarios for allocating agro-inputs and
management practices within heterogeneous farming environments.
Published by Copernicus Publications on behalf of the European Geosciences Union.
492 B. Vanlauwe et al.: Integrated soil fertility management in sub-Saharan Africa
1 Introduction
Integrated soil fertility management (ISFM) is a means to in-
crease crop productivity in a profitable and environmentally
friendly way (Vanlauwe et al., 2010) and thus to eliminate
one of the main factors that perpetuates rural poverty and
natural resource degradation in sub-Saharan Africa (SSA).
Current interest in ISFM partly results from widespread
demonstration of the benefits of typical ISFM interventions
at plot scale, including the combined use of organic ma-
nure and mineral fertilizers (e.g. Zingore et al., 2008), dual-
purpose legume–cereal rotations (e.g. Sanginga et al., 2003),
or micro-dosing of fertilizer and manure for cereals in semi-
arid areas (e.g. Tabo et al., 2007). ISFM is also aligned
to the principles of sustainable intensification (Pretty et al.,
2011; Vanlauwe et al., 2014a), one of the paradigms guid-
ing initiatives to increase the productivity of smallholder
farming systems. Sustainable intensification, though lacking
a universally accepted definition, usually comprises aspects
of enhanced crop productivity, maintenance and/or restora-
tion of other ecosystems services, and enhanced resilience to
shocks. ISFM can increase crop productivity and likely en-
hances other ecosystems services and resilience by diversi-
fying farming systems, mainly with legumes, and increasing
the availability of organic resources within farms, mainly as
crop residues and/or farmyard manure.
One of the principles of ISFM – the combined applica-
tion of fertilizer and organic resources – has been promoted
since the late 1980s (e.g. Vanlauwe et al., 2001), because of
(i) the failure of Green Revolution-like interventions in SSA
and (ii) the lack of adoption of low-external-input technolo-
gies by smallholder farmers, including herbaceous legume-
based technologies (e.g. Schulz et al., 2001). The combined
application of fertilizer and organic inputs made sense since
(i) both fertilizer and organic inputs are often in short supply
in smallholder farming systems due to limited affordability
and/or accessibility; (ii) both inputs contain varying combi-
nations of nutrients and/or carbon, thus addressing different
soil fertility-related constraints; and (iii) extra crop produce
can often be observed due to positive direct or indirect in-
teractions between fertilizer and organic inputs (Vanlauwe et
al., 2001). In 1994, Sanchez (1994) presented the “second
paradigm” for tropical soil fertility management, to “over-
come soil constraints by relying on biological processes by
adapting germplasm to adverse soil conditions, enhancing
soil biological activity, and optimizing nutrient cycling to
minimize external inputs and maximize their use efficiency”.
In this context, he already highlighted the need to integrate
improved germplasm, a second principle of ISFM, within
any improved strategy for nutrient management.
In 2010, with the renewed interest and investments in
boosting productivity of African agriculture, following the
Abuja Fertilizer Summit and the launch of the Alliance for
a Green Revolution in Africa (AGRA), ISFM was reconcep-
tualized with a focus on fertilizer use and the need for max-
imizing the agronomic efficiency (AE) of its nutrients and
consequently the value : cost ratio of its use. This reconcep-
tualization was driven by the recognition that crop produc-
tivity in SSA cannot be improved substantially without en-
hanced fertilizer use and took into account lessons learnt with
earlier approaches described above. Agronomic efficiency is
defined as extra crop yield produced per unit of fertilizer nu-
trient applied. Maximizing AE also minimizes the risk that
fertilizer nutrients move beyond the rooting zone into the en-
vironment and pollute water sources, a problem more typi-
cal for high input agriculture and less of a risk for African
agriculture (Vanlauwe and Giller, 2006). In this context, ap-
plying organic resources in combination with fertilizer can
enhance the AE of applied fertilizer through a range of direct
and indirect mechanisms (Vanlauwe et al., 2001) and the use
of improved germplasm is essential to ensure that the supply
of nutrients is matched with an equivalent demand for those
nutrients. ISFM was thus redefined as “A set of soil fertil-
ity management practices that necessarily include the use of
fertilizer, organic inputs, and improved germplasm combined
with the knowledge on how to adapt these practices to local
conditions, aiming at maximizing agronomic use efficiency
of the applied nutrients and improving crop productivity”.
“All inputs need to be managed following sound agronomic
principles” (Vanlauwe et al., 2010). This definition includes
a reference to “adaptation to local conditions”. The revised
conceptualization of ISFM also distinguished between re-
sponsive and non-responsive soils, both soils often occurring
within the same farm and the latter being soils on which no
significant response to “standard” fertilizer, or fertilizer that
is commonly available and often composed of N, P, and/or
K, can be observed (see Sect. 2 below) (Fig. 1).
This paper focuses on the “adaptation to local conditions”
of ISFM. “Local adaptation” refers to specific decision-
making processes in relation to the allocation of agro-inputs
and management practices at farm and plot level, thereby
recognizing production objectives, resource endowments,
and farm- and field-specific soil fertility conditions. Al-
though local adaptation was briefly discussed by Vanlauwe et
al. (2010), many questions have been raised in relation to the
understanding of this component of ISFM and the practices
associated with it. The objectives of the paper are therefore
(i) to conceptualize the local adaptation of ISFM, (ii) to il-
lustrate the impact of alleviating secondary constraints on the
fertilizer nutrient AE at plot scale, (iii) to illustrate the impact
of farm-level targeting of inputs and practices on fertilizer
nutrient AE at farm scale, (iv) to discuss the consequences of
the above on engaging extension agents and farmers with lo-
cal adaptation concepts and practices, and (v) to propose re-
search issues that require urgent attention for ISFM to move
to scale.
SOIL, 1, 491–508, 2015 www.soil-journal.net/1/491/2015/
B. Vanlauwe et al.: Integrated soil fertility management in sub-Saharan Africa 493
Figure 1. Conceptual relationship between the agronomic effi-
ciency (AE) of fertilizers and organic resource and the implemen-
tation of various components of ISFM, culminating in complete
ISFM towards the right side of the graph. Soils that are responsive to
NPK-based fertilizer and those that are poor and less responsive are
distinguished. Path A indicates anticipated increases in AE when
fertilizer is applied using appropriate agronomic practices in com-
bination with adapted germplasm. Paths B and C refer to the need
for addressing non-responsiveness (C) before increases in AE can
be expected on non-responsive soils, even after application fertilizer
in combination with adapted germplasm (B). Source: Vanlauwe et
al. (2010).
2 Conceptualization of local adaptation
Since the formulation of the second paradigm (Sanchez,
1994) and with the renewed focus on making fertilizer ac-
cessible to and profitable for smallholder farmers, several
insights have been gathered that influence fertilizer nutri-
ent AE and thus need to be integrated in the definition of
ISFM. Smallholder farming systems in SSA are very diverse,
ranging from semi-nomadic pastoralism in very arid envi-
ronments to shifting cultivation in the humid tropical forests.
Although strongly driven by agro-ecological conditions, this
diversity has also been influenced through the interplay of,
amongst other things, local cultures, infrastructure, distance
to markets, and socioeconomic opportunities outside agricul-
ture. African farming areas have been described at continen-
tal scale under 13 main categories (Dixon et al., 2001), but
such simplification masks huge local diversity, which makes
generalization of productivity-enhancing recommendations
for SSA problematic (Giller, 2013). Nevertheless, repeating
patterns can be observed across different African farming
systems that have important implications for ISFM.
2.1 Patterns of soil fertility conditions within smallholder
farms
First of all, a number of factors determine the fertility of
soils: (i) parent material, (ii) soil formation processes like
weathering operating at a timescale of thousands of years,
and (iii) human management operating over much shorter
timescales. The processes of soil formation and of soil re-
distribution through erosion and deposition give rise to the
soilscape with typical patterns of soil types associated with
slope position across the landscape. Soils can be more grav-
elly and thinner with rock outcrops close to hill tops, with
more fertile soils in mid-slope positions and fertile, alluvial
soils in the valleys. Superimposed on the soilscape is a pat-
tern created by human management. Apart from a few ex-
ceptions, such as the home-garden agroforestry systems of
southern Ethiopia (Abebe et al., 2010), intensive sedentary
agriculture is less than 100 years old in the majority of SSA
and has been changing rapidly with very rapid growth of hu-
man population. Two opposing factors have driven the de-
velopment of patterns of soil fertility (Giller et al., 2006).
On the one hand, increasing pressure on land and the disap-
pearance of fallows have led to intensive cropping which in
turn depleted the soils of nutrients. On the other hand, nutri-
ents, concentrated through manure, have been applied to part
of the farm – often the fields close to the homestead. These
opposing processes give rise to patterns of soil fertility, as
depicted conceptually in Fig. 2. For instance, in the “ring
management” pattern in West Africa, a circle of more fer-
tile soil close to houses is surrounded by poor soils and then
increasingly fertile soil with distance from the settlement
as bush fields further from the village are cropped less fre-
quently (Prudencio, 1993; Ruthenberg, 1980). In the Bukoba
region of western Tanzania, cattle were used to harvest nu-
trients to develop fertile banana–coffee–food crop gardens
(bibanja) in a sea of extensive grasslands (rweya) (Baijukya
et al., 2005). The reasons that farmers concentrate their nu-
trient resources on the home fields are manifold: the home
field provides grain for the food security of the household,
nutrient resources are often in short supply and insufficient
to apply to all of the fields, the home fields are less suscepti-
ble to theft, and it is more convenient and requires less labour
to transport manure (Misiko et al., 2011).
Fertile home fields need only maintenance fertilization to
sustain good crop yields, and crop response to fertilizer in
strongly depleted soils is often weak due to a suite of nutrient
deficiencies (Fig. 3; Vanlauwe et al., 2006). For example, on
depleted outfields on sandy granitic soils in Zimbabwe, crop
response to N and P fertilizers was limited by deficiencies
of Zn, Ca, Mg, and K (Zingore et al., 2008). Such depleted
fields have been described as “non-responsive soils”, or soils
that have been degraded to an extent that the application of
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494 B. Vanlauwe et al.: Integrated soil fertility management in sub-Saharan Africa
Figure 2. High-resource-endowed farms (HRE) tend to have more
cattle and manure and can maintain good soil fertility and crop
yields across all of their fields. Low-resource-endowed farms (LRE)
have no livestock and manure and their fields are often uniformly
poor in soil fertility and crop yields. Farmers of intermediate re-
source endowment (MRE) have limited resources that they apply
preferentially to the home fields, creating strong gradients of soil
fertility. This allows the classification of fields across the different
farms into three types: fertile home fields, moderately fertile middle
fields, and poorly fertile outfields for three farmer typologies (HRE,
MRE, and LRE) (cf. Zingore et al., 2007a).
NPK fertilizer does not result in increased crop productivity
(Vanlauwe et al., 2010). Such soils are common in densely
populated areas where mineral and/or organic inputs are in
short supply and the generation of non-responsiveness can be
a combination of chemical (e.g. soil acidification, micronu-
trient deficiencies), physical, (e.g. topsoil erosion, hardpan
formation), and/or biological (e.g. soil-borne pests and dis-
eases) mechanisms. Obviously, the AE of fertilizer nutrients
applied on non-responsive soils is very low to zero and crop
yield increases agronomically and/or economically insignifi-
cantly.
2.2 Farmer typologies, resource endowments, and
production objectives within smallholder farming
communities
A second commonly observed pattern is the diversity of re-
source endowments and farm types within farming commu-
nities (Fig. 2; Tittonell et al., 2010). Drivers operating at dif-
ferent scales generate a diversity of farming households in
relation to available on- and off-farm resources and produc-
tion objectives. Whereas relatively poor families often culti-
vate more degraded soils (Tittonell and Giller, 2013), fami-
lies with a relatively higher resource endowment have more
options to purchase and allocate fertilizer and organic in-
puts across the various plots within their farms. The latter
are also usually less risk-averse and thus more open to ex-
plore alternative agricultural practices within their farm. Soil
fertility gradients are often clearest on farms of intermedi-
ate resource endowment, as conceptually depicted in Fig. 2.
Figure 3. Simulated crop yield with the model FIELD as a function
of mineral N application rates for different soil fertility zones on
sand (a) and clay (b) soils and nutrient management options (only
mineral N, manure at 10 t ha−1 and mineral N, and mineral P at
20 kg ha−1 and mineral N) (refer to Zingore et al., 2011, for a de-
tailed soil characterization and description of the FIELD model).
Besides access to resources, farmers have different produc-
tion objectives. For instance, in western Kenya, Tittonell et
al. (2005) identified that some small farms were owned by
wealthy households which had external income from pen-
sions or remittances and for whom farming is not their pri-
mary income. Such households are not expected to consider
agricultural investments a priority. In contrast, well-resource-
endowed farmers with large areas of land make a relatively
good living from farming. Poor households with very small
farms have limited access to resources, often selling their
labour to other households, and are thus expected to apply
fewer or no agro-inputs on their farms.
2.3 Limitations of improved germplasm and organic
resources to maximize fertilizer AE
Organic resources can enhance the AE of fertilizer nutri-
ents through a number of mechanisms, including “direct”
(e.g. temporary N immobilization) and “indirect” interac-
tions (e.g. temporary alleviation of soil acidity constraints
and supply of other yield-limiting nutrients) (Vanlauwe et al.,
2001). Improved germplasm can equally enhance AE of fer-
tilizer nutrients by ensuring a higher demand for applied nu-
trients. For certain constraints, however, organic resource ap-
plication and improved germplasm are not a suitable solution
and other amendments or practices are required (Table 1).
SOIL, 1, 491–508, 2015 www.soil-journal.net/1/491/2015/
B. Vanlauwe et al.: Integrated soil fertility management in sub-Saharan Africa 495
Table 1. A selected set of constraints that can prevent the uptake of nutrients applied with “standard” fertilizer – or fertilizer that is commonly
available and often composed of N, P, and/or K – and the potential of improved germplasm, organic resources
