Conservation agriculture in eastern and southern provinces of Zambia: Long-term effects on soil quality and maize productivity
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Soil & Tillage Research 126 (2013) 246258
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Soil & Tillag
Frequent crop failures and periodic famines are commonthreats to rural farming communities in southern Africa. Unreli-able climatic conditions characterised by frequent droughts andthe potential impacts of climate change (Lobell et al., 2008), as wellas decreasing soil fertility, are major constraints (Kumwenda et al.,1997; Mapfumo and Giller, 2001; Zingore et al., 2005). As a result,there is an increased need for more resilient, water-conserving,productive and sustainable agriculture cropping systems (Thier-felder and Wall, 2010a; Wall, 2007).
Since the 1990s, environmentally sustainable agriculturesystems that improve soil fertility and production capacity haveincreasingly gained attention in research and extension services
in southern Africa (Mafongoya et al., 2006). In support of this,international agriculture research and donor organisations havestarted to promote new systems based on the principles andpractices of conservation agriculture (CA) (Mashingaidze et al.,2006; Mazvimavi and Twomlow, 2009; Mazvimavi et al., 2008;Steiner, 1998). CA is a cropping system originally developed inthe Americas and Australia that combines three key principles:(i) minimum soil disturbance, i.e. no soil inversion by the hoe orthe mouldboard plough; (ii) in situ crop residue retention ofavailable plant material (living or dead) on the soil surface; and(iii) crop rotations and associations to reduce and overcome pestand disease problems in the system (FAO, 2002; Kassam et al.,2009). CA is a complex but fairly exible agricultural systemthat can be widely adapted to local site conditions (Wall, 2007).On the other hand, CA is not a xed recipe, blanketrecommendation or panacea, and there is therefore a need totake into account the conditions and socio-economic constraintsof farmers.
A R T I C L E I N F O
Received 9 May 2012
Received in revised form 8 September 2012
Accepted 11 September 2012
Sustainable land management
A B S T R A C T
Sustainable and resilient cropping systems are required in southern Africa to arrest declining soil fertility
and offset the future negative effects of climate change. Conservation agriculture (CA) has been proposed
as a potential system for improving soil quality and providing stable yields through minimum soil
disturbance, surface crop residue retention (mulching) and crop rotations or associations. However,
concerns have been raised about the lack of evidence of the benets of CA for small-scale farmers in
southern Africa. This research was carried out in two communities and one on-station site in Zambia to
provide more scientic evidence about the effects of CA on soil quality, inltration, soil moisture and
crop performance. Results from Kayowozi showed that maize yields in a direct seeded CA treatment,
using cowpea seeded with a dibble stick in full rotation, increased by up to 78% after four cropping
seasons in comparison to a conventional control using a ridge and furrow system. At Malende, maize
yields for animal traction rip-line seeded and direct seeded plots were, on average, 75% and 91% higher
than a conventionally tilled control plot after six cropping seasons. Detailed studies undertaken at the
Monze Farmer Training Centre revealed that CA treatments, especially that using cotton in rotation,
increased water inltration and soil moisture. In some years, inltration was ve times higher on CA
elds than on those using conventional tillage. Carbon increases were only found at the on-station long-
term trial, where, over time, CA plots outperformed conventional practice leading to an overall increase
of 12% carbon in the rst 30 cm, compared with decreases of 15% in the conventional control.
Comparative analyses between the on-farm and on-station trials point to a lack of adequate mulching,
which might be the reason for lower carbon at the on-farm sites. We conclude that the effects of CA can
build up on different soil types in most systems, but that scaling up and out requires the whole
community to be targeted, rather than relying on individual farmers to overcome constraints related to
the set-up in rural communities.
2012 Elsevier B.V. All rights reserved.
* Corresponding author. Tel.: +263 772815230.
E-mail address: firstname.lastname@example.org (C. Thierfelder).
0167-1987/$ see front matter 2012 Elsevier B.V. All rights reserved.http://dx.doi.org/10.1016/j.still.2012.09.002Conservation agriculture in eastern and seffects on soil quality and maize produc
Christian Thierfelder a,*, Mulundu Mwila b, Leonarda CIMMYT, P.O. Box MP 163, Mount Pleasant, Harare, Zimbabweb Zambia Agriculture Research Institute (ZARI), Farming Systems and Social Sciences Div
jou r nal h o mep age: w wwuthern provinces of Zambia: Long-termivity
n, P.O. Box 510089, Chipata, Zambia
l s evier . co m/lo c ate /s t i l l
C. Thierfelder et al. / Soil & Tillage Research 126 (2013) 246258 247Farmers in southern Africa rely on maize (Zea mays L.) as themain staple food crop: it accounts for 5090% of the caloric intake(Dowswell et al., 1996). Sorghum (Sorghum bicolor L.), grainlegumes such as common bean (Phaseolus vulgaris L.), cowpea(Vigna unguiculata L.), groundnut (Arachis hypogaea), cassava(Manihot esculenta Crantz), sweet potatoes (Ipomoea batatas (L.)Lam) and a variety of vegetables are the other important foodcrops. Traditionally, the mouldboard plough and hand hoe are usedfor land preparation and planting. Maize is sown into tilled moistsoil. Maize is often grown as a continuous monoculture, neglectingthe fact that rotations are important in the agricultural system.Legume crops are seldom grown due to poorly developed markets,land area limitation, and lack of good quality seed, and thus thereturns from rotational crops do not justify their systematicproduction (Snapp et al., 2002; Thierfelder and Wall, 2010b). Inmixed croplivestock systems, there is competition for cropresidues between mulching and livestock for feed (Baudron et al.,2012b; Giller et al., 2009; Mueller et al., 2001; Valbuena et al.,2012). Farmers also use this valuable resource for fuel andbuilding. In some areas the residues are burned because there is noassociated value involved and termites, especially on loamy andclay soils, make it difcult to retain enough residues (Thierfelderand Wall, 2012). As a result, the soil surface in maize elds is oftenuncovered and, when exposed to heavy rainfall, build up surfaceseals and crusts which reduces rainfall inltration leading to moresurface run-off and soil erosion (Derpsch et al., 1986; Roth et al.,1988; Thierfelder et al., 2005; Thierfelder and Wall, 2009).Insufcient return of organic matter, combined with excessivesoil tillage in many cases, increases physical, chemical andbiological soil degradation, which is regarded as one of the rootcauses for declining yields in tropical environments, despite thehigh yield potential of crop cultivars (Derpsch et al., 1986, 1991;Kassam et al., 2009; Lal, 1974; Stagnari et al., 2010).
Currently there are a number of technology options available toplant crops under CA (Johansen et al., 2012). The main plantingsystem promoted in Zambia and Zimbabwe since the mid 1990s isbased on manually dug planting basins, a similar system to the zaisystem in the Sahel (Haggblade and Tembo, 2003; Mazvimavi et al.,2008; Twomlow et al., 2006). Another manual CA planting systempromoted in southern Africa is the planting stick (dibble stick),based on a pointed stick used to dig two small planting holes, onefor seed and one for fertiliser. Plant spacing is easy to adjust andstrings with marks are used as guidance for planting stations. Amore mechanized option has been introduced in the form ofmanual jab planters (matracas); however, they are currentlyneither widely available nor used. Farmers with access to animaldraught power can use two distinct systems: (i) manual seedingand fertilisation in previously formed rip-lines created by a Magoyefurrow opener or other ripper tine attachments mounted on theplough beam (GART, 2006); and (ii) direct planting and fertilisationwith an animal traction direct planter from Irmaos FitarelliMaquinas Agricolas, Brazil, or locally produced Jambo directseeders from Grownet Investment, Zimbabwe (Johansen et al.,2012).
CA has potential to improve water inltration and reduceerosion, improve soil aggregation, reduce soil compaction, increasesurface soil organic matter and soil carbon content, regulate soiltemperature, suppress weeds, reduce costs of production, savetime and reduce greenhouse gas emissions. Benets have beenhighlighted by previous reviews (see e.g. Govaerts et al., 2009;Hobbs, 2007; Kassam et al., 2009; Wall, 2007). However, thefeasibility and applicability of CA under the specic circumstancesof farmers in southern Africa is questionable (Baudron et al.,2012a; Bolliger, 2007; Giller et al., 2009; Guto et al., 2012). There isa need for locally generated quantitative data to improveknowledge on the benets and challenges of various CA systemsand to provide evidence that CA is feasible in the farming systemsin southern Africa (Giller et al., 2011), despite the biophysical andsocio-economic constraints (e.g. residue retention, weed control,equipment availability, physical and nancial access to inputs,land tenure, knowledge gaps and mindset) highlighted by Wall(2007).
The aim of this study was to investigate the effects of