Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Cost-benefit analysis of conservation agriculture implementation in Syrdarya province of Uzbekistan
    Daujanov, Azizbek ; Groeneveld, R.A. ; Pulatov, Alim ; Heijman, W.J.M. - \ 2016
    Visegrad Journal on Bioeconomy and Sustainable Development 5 (2016)2. - ISSN 1339-3367 - p. 48 - 52.
    cost-benefit analysis - conservation agriculture - permanent bed system - Uzbekistan
    Most irrigated lands of Central Asia suffer from land degradation, and unsustainable Agricultural practices are one of the factors contributing to land degradation. Conservation agriculture (CA) is seen as a way to mitigate land degradation and rationalize resource use. The aim of this article is to investigate the efficiency of CA implementation in the Syrdarya province of Uzbekistan, Central Asia by carrying out a cost-benefit analysis (CBA). The CBA was conducted for a hypothetical situation where the farm decides to switch from conventional agricultura to CA. Unlike the previous studies, this study investigates complete crop rotation cycle in the long-term period. The study outcomes suggest that investment in CA implementation results in positive incremental benefit if the advantages of CA are monetized.
    A socioeconomic analysis of the zaï farming practice in northern Burkina Faso
    Schuler, Johannes ; Voss, Anna ; Ndah, Hycenth Tim ; Traore, Karim ; Graaff, Jan de - \ 2016
    Agroecology and Sustainable Food Systems 40 (2016)9. - ISSN 2168-3565 - p. 988 - 1007.
    Adoption - conservation agriculture - food security - land degradation - livelihood

    The zaï farming practice is a local adaptation of conservation agriculture to degraded semiarid areas and consists of restoring heavily crusted soils through small planting pits. This article analyzes the land use change and its impacts through the zaï farming practice in the northern part of Burkina Faso from a socioeconomic perspective, based on data gathered through two surveys in the Ouahigouya region. A survey among 101 farmers concentrated mainly on adoption rates and household characteristics. Later, 16 farmers from the first survey were interviewed with respect to their adoption of the zaï technique for soil restoration. Farm data was collected to cover the farms’ and households’ expenses and revenues for the year 2011. Material and labor input, as well as the obtained yields, were analyzed using the economic farm model OLYMPE. The results reflect the positive economic benefits of zaï cereal production at field and farm level when compared to conventional cultivation, but also point out the constraints to its further expansion. Despite higher input costs mostly related to external labor, the increased yields led to a more than three times higher gross margin per hectare for zaï millet (101,085 FCFA) than the conventional system (23,030 FCFA). Yet, the physically demanding intensive labor requirements during land preparation and implementation of the planting pits (+117 % man days/ha) challenge a broader adoption of the zaï practice. Nonetheless, in a mostly subsistence-oriented farming context the zaï practice proved to reverse severe land degradation and improve households’ livelihood and food security.

    Economic trade-offs of biomass use in crop-livestock systems: Exploring more sustainable options in semi-arid Zimbabwe
    Homann Kee, S. ; Valbuena Vargas, D.F. ; Masikati, P. ; Descheemaeker, K.K.E. ; Nyamangara, J. ; Claessens, L.F.G. ; Erenstein, O. ; Rooyen, A.F. van; Nkomboni, D. - \ 2015
    Agricultural Systems 134 (2015). - ISSN 0308-521X - p. 48 - 60.
    conservation agriculture - smallholder farmers - intensification - productivity - challenges - strategies - countries - benefits - tropics - africa
    In complex mixed crop-livestock systems with limited resources and biomass scarcity, crop residues play an important but increasingly contested role. This paper focuses on farming systems in the semi-arid areas of Zimbabwe, where biomass production is limited and farmers integrate crop and livestock activities. Conservation Agriculture (CA) is promoted to intensify crop production, emphasizing the retention of surface mulch with crop residues (CR). This paper quantifies the associated potential economic tradeoffs and profitability of using residues for soil amendment or as livestock feed, and explores alternative biomass production options. We draw on household surveys, stakeholder feedback, crop, livestock and economic modeling tools. We use the Trade-Off Analysis Model for Multi Dimensional Impact Assessment (TOA-MD) to compare different CR use scenarios at community level and for different farm types: particularly the current base system (cattle grazing of maize residues) and sustainable intensification alternatives based on a CA option (mulching using maize residues ± inorganic fertilizer) and a maize– mucuna (Mucuna pruriens) rotation. Our results indicate that a maize–mucuna rotation can reduce trade-offs between CR uses for feed and mulch, providing locally available organic soil enhancement, supplementary feed and a potential source of income. Conservation Agriculture without fertilizer application and at non-subsidized fertilizer prices is not financially viable; whereas with subsidized fertilizer it can benefit half the farm population. The poverty effects of all considered alternative biomass options are however limited; they do not raise income sufficiently to lift farmers out of poverty. Further research is needed to establish the competitiveness of alternative biomass enhancing technologies and the socio-economic processes that can facilitate sustainable intensification of mixed crop-livestock systems, particularly in semi-arid environments.
    Exclusion of soil macrofauna did not affect soil quality but increases crop yields in a sub-humid tropical maize-based system
    Paul, B.K. ; Vanlauwe, B. ; Hoogmoed, M. ; Hurisso, T.T. ; Ndabamenye, T. ; Terano, Y. ; Ayuke, F.O. ; Pulleman, M.M. - \ 2015
    Agriculture, Ecosystems and Environment 208 (2015). - ISSN 0167-8809 - p. 75 - 85.
    conservation agriculture - organic-matter - microaggregate formation - agroecosystem function - aggregate stability - food security - termites - africa - tillage - biodiversity
    Soil macrofauna such as earthworms and termites are involved in key ecosystem functions and thus considered important for sustainable intensification of crop production. However, their contribution to tropical soil and crop performance, as well as relations with agricultural management (e.g. Conservation Agriculture), are not well understood. This study aimed to quantify soil macrofauna and its impact on soil aggregation, soil carbon and crop yields in a maize-soybean system under tropical sub-humid conditions. A field trial was established in Western Kenya in 2003 with tillage and residue retention as independent factors. A macrofauna exclusion experiment was superimposed in 2005 through regular insecticide applications, and measurements were taken from 2005 to 2012. Termites were the most abundant macrofauna group comprising 61% of total macrofauna numbers followed by ants (20%), while few earthworms were present (5%). Insecticide application significantly reduced termites (by 86 and 62%) and earthworms (by 100 and 88%) at 0-15 and 15-30 cm soil depth respectively. Termite diversity was low, with all species belonging to the family of Macrotermitinae which feed on wood, leaf litter and dead/dry grass. Seven years of macrofauna exclusion did not affect soil aggregation or carbon contents, which might be explained by the low residue retention and the nesting and feeding behavior of the dominant termites present. Macrofauna exclusion resulted in 34% higher maize grain yield and 22% higher soybean grain yield, indicating that pest damage – probably including termites - overruled any potentially beneficial impact of soil macrofauna. Results contrast with previous studies on the effects of termites on plant growth, which were mostly conducted in (semi-) arid regions. Future research should contribute to sustainable management strategies that reduce detrimental impact due to dominance of potential pest species while conserving soil macrofauna diversity and their beneficial functions in agroecosystems.
    Trade-offs around the use of biomass for livestock feed and soil cover in dairy farms in the Alaotra lake region of Madagascar. Special Issue: Biomass use trade-offs in cereal cropping systems: Lessons and implications from the developing world
    Naudin, K. ; Bruelle, G. ; Salgado, P. ; Penot, E. ; Lubbers, M.T.M.H. ; Ridder, N. de; Giller, K.E. - \ 2015
    Agricultural Systems 134 (2015). - ISSN 0308-521X - p. 36 - 47.
    cropping systems - conservation agriculture - physical-properties - zero-tillage - south-asia - residue - africa - maize - rice - productivity
    Conservation agriculture (CA) is promoted as a promising technology to stabilize or improve crop yields in Africa and Madagascar. However, small-scale farmers face difficulties to retain soil cover, mainly because of competing uses for the biomass produced, especially to feed cattle. To explore the relation between dairy production and CA we developed an optimisation model at farm level. Our aim was to explore trade-offs between CA practices and the size of dairy cow herds. Our model includes three main components: the farm, the crops and the cattle herd. The optimisation was made on the total net income for three years. Biomass produced by cropping activities can either serve as mulch or to feed cows. We applied a constraint on the minimum soil cover % to keep at the end of each year for CA fields: from 30% to 95%. We simulated two scenarios of milk market: a small milk market with low forage price and an open milk market scenario with higher price of forage. Three prototypes of farms were simulated with different proportion and size of four kinds of field. These three prototypes were: medium-sized farm with hillsides dominating, medium-sized farm with paddy fields dominating and small-sized farm with hillsides. Changing the degree of soil cover to be retained on CA plots did not significantly modify the total net farm income. It was more strongly influenced by the characteristics of the milk market. In case of a limited milk market it was not profitable to have more than seven cows because the expenses were not compensated by animal production. When setting minimum soil cover to 30% then all of the simulated results include biomass coming from CA cropping system even with 12 cows/farm. Conversely when setting this constraint to 95%, above 6/7 cows/farm forage come only from conventional fields. In all of the situations simulated even with 6 cows, with the current and twice the price for forage, it was possible to keep at least 50% of soil cover on 30–60% of the total farm area. CA was not feasible for farms with no irrigated paddy fields or when forage fetched a high price regardless of the constraint for % of soil cover to be kept on CA fields. Overall, CA systems can be beneficial for dairy cow farmers due to the forage produced, although the milk market and thus the value of biomass for forage, has a strong influence on CA practice at field level.
    From farm scale synergies to village scale trade-offs: Cereal crop residues use in an agro-pastoral system of the Sudanian zone of Burkina Faso
    Andrieu, N. ; Vayssières, J. ; Corbeels, M. ; Blanchard, M. ; Vall, E. ; Tittonell, P.A. - \ 2015
    Agricultural Systems 134 (2015). - ISSN 0308-521X - p. 84 - 96.
    west-african savanna - sub-saharan africa - livestock systems - conservation agriculture - fertility management - phosphorus budget - soil fertility - spatial carbon - nitrogen - flows
    Traditionally, cereal crop harvest residues are communally grazed by the ruminant herds of villagers and transhumant pastoralists in the agro-pastoral systems which predominate in the savannah zone of West Africa. We analysed the impact of the private use of crop residues by individual farmers on crop and livestock productivity at three scales: the field, farm, and village. We collected data in the village of Koumbia, located in the Sudanian region of Burkina Faso. Three types of farmers were identified: resource-poor farmers, predominantly livestock farmers, and resource-rich farmers. The trade-offs between different uses and users of cereal crop residues at the three scales were analysed through field surveys and a simple model of biomass flows. We considered current communal use practices and two alternative scenarios of private cereal crop residue use: (i) for composting (fertility scenario) and (ii) as fodder (fodder scenario). Our analysis of current practices confirmed that farmers left around 80% of cereal crop residues on their fields. Soil fertility for cereal production therefore could be improved through crop residue management at the farm scale. We also found that communal grazing benefited farmers with high numbers of livestock. Maize grain production at the farm scale was improved in both of the simulated scenarios. Yet these scenarios had a negative impact on fodder self-sufficiency at the village scale, and on the N balance of the savannah-derived rangelands. The negative impact was greater in the fertility scenario than the fodder stock scenario. Increasing cereal productivity at the farm scale cannot be achieved without considering the trade-offs involved at the village scale. Changes in practices will require negotiations between the different types of farmers involved. Participatory innovation platforms with discussion support tools like the model presented in our study can facilitate such negotiations.
    Feeding, crop residue and manure management for integrated soil fertility management - A case study from Kenya
    Castellanos Navarrete, A. ; Tittonell, P.A. ; Rufino, M.C. ; Giller, K.E. - \ 2015
    Agricultural Systems 134 (2015). - ISSN 0308-521X - p. 24 - 35.
    smallholder farming systems - western kenya - conservation agriculture - livestock systems - cycling efficiencies - exploring diversity - carbon dynamics - dairy-cows - highlands - resource
    Western Kenya is one of Africa’s most densely populated rural areas, characterised by intensive smallholder crop–livestock systems on degraded lands managed with small inputs of mineral fertiliser and animal manure. Competing uses for crop residues and other organic resources often results in poor nutrient cycling efficiencies at farm scale. Modifying livestock feeding, retaining more crop residues in the field, and improving manure management can help conserving considerable amount of nutrients on-farm. To examine to what extent such strategies would be feasible, we analysed whole-farm nutrient cycling efficiencies (NCE) of a range of farms differing in resource-endowment and production orientation, identifying the most efficient farmer strategies considering labour and financial constraints. Nutrient concentration in excreted cattle manure was relatively small (i.e., N <1.7%; P <0.6%). Current manure management practices led to low NCE’s (average 27%) due to nutrient losses from excretion through storage and application. Farmers have few incentives to improve manure management given the small amounts of excreta and nutrients to be recycled. Yet, manure, both composted and fresh, represented the greatest N (16 kg ha-1 season-1) and C returns to the soil (312 kg C ha-1 season-1). Retention of crop residues was the cheapest source of nutrient inputs for the next crop, especially when compared with manure, but farmers prioritised its use for cattle feeding. Our findings highlight the critical lack of nutrients and organic residues on smallholder farms in the densely-populated highlands of East Africa, as well as low NCE when it comes to manure. In these conditions, efficient nutrient cycling for manure and improved cattle feeding are essential to increase use efficiencies of any possible external nutrient added in these farms.
    Multi-scale trade-off analysis of cereal residue use for livestock feeding vs. soil mulching in the Mid-Zambezi Valley, Zimbabwe
    Baudron, F. ; Delmotte, S. ; Corbeels, M. ; Herrera, J.M. ; Tittonell, P.A. - \ 2015
    Agricultural Systems 134 (2015). - ISSN 0308-521X - p. 97 - 106.
    conservation agriculture - systems - nitrogen - africa - model - knowledge - village - quality - carbon - apsim
    Cereal residues represent a major resource for livestock feeding during the dry season in southern Africa. When kept on the soil surface instead of feeding them to livestock, crop residues can contribute to increasing soil fertility and maintaining crop productivity in the short- and the long-term. We explored these trade-offs for smallholder cotton–sorghum farming systems in the semi-arid Zambezi Valley, northern Zimbabwe. The analysis was done using simulation models at three scales, the plot, the farm and the territory, to simulate the effects of different sorghum residue allocations to livestock feeding vs. soil mulching, in combination with different application rates of mineral nitrogen fertilizer on crop productivity. The plot-scale simulations suggest that without N fertilization soil mulching has a positive effect on cotton yields only if small quantities of sorghum residues are used as mulch (average cotton yields of 2.24 ± 0.41 kg ha-1 with a mulch of 100 kg ha-1 vs. 1.91 ± 0.29 kg ha-1 without mulch). Greater quantities of mulch have a negative effect on cotton yield without N fertilization due to N immobilization in the soil microbial biomass. With applications of 100 kg N ha-1, quantities of mulch up to 3 t ha-1 have no negative effect on cotton yield. Results at farm-scale highlight the fundamental role of livestock as a source of traction, and the need to feed a greater proportion of sorghum residues to livestock as herd and farm sizes increase. Farmers with no livestock attained maximum crop production when 100% of their sorghum residue remained in the field, as they do not have access to cattle manure. The optimum fraction of crop residue to be retained in the fields for maximum farm crop production varied for farmers with 2 or less heads of cattle (80% retention), with 2–3 heads (60–80%), with 4 or more heads (40–60%). At the scale of the entire territory, total cotton and sorghum production increased with the density of cattle, at the expense of soil mulching with crop residues. The results of our simulations suggest that (i) the optimum level of residue retention depends on the scale at which trade-offs are analyzed; (ii) the retention of all of the crop residue as mulch appears unrealistic and undesirable in farming systems that rely on livestock for traction; and (iii) crop residue mulching could be made more attractive to farmers by paying due attention to balancing C to N ratios in the soil and by promoting small-scale mechanization to replace animal traction.
    The way forward in biochar research: targeting trade-offs between the potential wins
    Jeffery, S.L. ; Bezemer, T.M. ; Cornelissen, G. ; Kuyper, T.W. ; Lehmann, J. ; Mommer, L. ; Sohi, S.P. ; Voorde, T.F.J. van de; Wardle, D.A. ; Groeningen, J.W. van - \ 2015
    Global change biology Bioenergy 7 (2015)1. - ISSN 1757-1693 - p. 1 - 13.
    life-cycle assessment - soil organic-matter - black carbon - climate-change - conservation agriculture - sustainable agriculture - pyrolysis temperature - anaerobic-digestion - chemical-properties - nitrogen dynamics
    Biochar application to soil is currently widely advocated for a variety of reasons related to sustainability. Typically, soil amelioration with biochar is presented as a multiple-‘win’ strategy, although it is also associated with potential risks such as environmental contamination. The most often claimed benefits of biochar (i.e. the ‘wins’) include (i) carbon sequestration; (ii) soil fertility enhancement; (iii) biofuel/bioenergy production; (iv) pollutant immobilization; and (v) waste disposal. However, the vast majority of studies ignore possible trade-offs between them. For example, there is an obvious trade-off between maximizing biofuel production and maximizing biochar production. Also, relatively little attention has been paid to mechanisms, as opposed to systems impacts, behind observed biochar effects, often leaving open the question as to whether they reflect truly unique properties of biochar as opposed to being simply the short-term consequences of a fertilization or liming effect. Here, we provide an outline for the future of soil biochar research. We first identify possible trade-offs between the potential benefits. Second, to be able to better understand and quantify these trade-offs, we propose guidelines for robust experimental design and selection of appropriate controls that allow both mechanistic and systems assessment of biochar effects and trade-offs between the wins. Third, we offer a conceptual framework to guide future experiments and suggest guidelines for the standardized reporting of biochar experiments to allow effective between-site comparisons to quantify trade-offs. Such a mechanistic and systems framework is required to allow effective comparisons between experiments, across scales and locations, to guide policy and recommendations concerning biochar application to soil.
    Analysis of trade-offs in agricultural systems: current status and way forward
    Klapwijk, C.J. ; Wijk, M.T. van; Rosenstock, T.S. ; Asten, P.J.A. van; Thornton, P.K. ; Giller, K.E. - \ 2014
    Current Opinion in Environmental Sustainability 6 (2014)2. - ISSN 1877-3435 - p. 110 - 115.
    crop-livestock systems - land-use - conservation agriculture - management-practices - climate-change - africa - strategies - knowledge - resource - science
    Trade-off analysis has become an increasingly important approach for evaluating system level outcomes of agricultural production and for prioritizing and targeting management interventions in multifunctional agricultural landscapes. We review the state-of-the-art for trade-off analysis, assessing different techniques by exploring a concrete example of trade-offs around the use of crop residues in smallholder farming systems. The techniques for performing trade-off analyses have developed substantially in recent years aided by mathematical advancement, increased computing power, and emerging insights into systems behaviour. Combining different techniques allows the assessment of aspects of system behaviour via various perspectives, thereby generating complementary knowledge. However, this does not solve the fundamental challenge: trade-off analyses without substantial stakeholder engagement often have limited practical utility for informing practical decision-making. We suggest ways to integrate approaches and improve the potential for societal impact of future trade-off analyses.
    Systems approaches to innovation in crop protection. A systematic literature review
    Schut, M. ; Rodenburg, J. ; Klerkx, L.W.A. ; Ast, A. van; Bastiaans, L. - \ 2014
    Crop Protection 56 (2014). - ISSN 0261-2194 - p. 98 - 108.
    integrated pest-management - sub-saharan africa - agricultural innovation - conservation agriculture - weed management - food security - sustainable agriculture - rice intensification - disease management - changing climate
    The objective of this paper is to explore the extent to which systems approaches to innovation are reflected in the crop protection literature and how such approaches are used. A systematic literature review is conducted to study the relation between crop protection and systems approaches to innovation in 107 publications. The analysis of the crop protection literature demonstrates that only a small fraction is systems-oriented as compared to the bulk of publications with a technology-oriented approach. The analysis of agricultural innovations systems literature shows that, although crop protection is addressed, the potential of this systems approach remains largely unexplored for crop protection innovation. A large share of the publications included in this review focus on cropping or farming ‘systems’ while ‘innovation’ often equals the development, transfer, adoption and diffusion of crop protection technologies at farm level. There is relatively little attention for the institutional and political dimensions of crop protection and the interactions between farm, regional and national levels in crop protection systems. The traditional division of roles and responsibilities of researchers as innovators, extension personnel as disseminators, and farmers as end-users, is challenged only to a limited extent. The majority of publications discusses ways to optimise existing features of crop protection systems, without exploring more structural transformations that may be required to enhance the resilience of crop protection systems.
    Response to 'Combining sustainable agricultural production with economic and environmental benefits'
    Sumberg, J. ; Andersson, J.A. ; Giller, K.E. ; Thompson, J. - \ 2013
    Geographical Journal 179 (2013)2. - ISSN 0016-7398 - p. 183 - 185.
    rice intensification sri - conservation agriculture - production systems - management - madagascar - yield - opportunities - farmers - africa - india
    We suggest that a recent commentary piece in The Geographical Journal on Conservation Agriculture (CA) and the System of Rice Intensification (SRI) (Kassam and Brammer 2012 was misleading because it drew very selectively from the literature, and presented its conclusions as both widely accepted and uncontroversial. Kassam and Brammer's intervention in the continuing debates around CA and SRI can be understood as a manifestation of the new ‘contested agronomy’. While Kassam and Brammer call on geographers to do research that will promote the spread of CA and SRI, we suggest that this misconstrues and devalues the potential contribution of geography and social science more generally to agricultural development.
    Land use and management effects on soil organic matter fractions in Rhodic Ferralsols and Haplic Arenosols in Bindura and Shamva districts of Zimbabwe
    Mujuru, L. ; Mureva, A. ; Velthorst, E.J. ; Hoosbeek, M.R. - \ 2013
    Geoderma 209-210 (2013). - ISSN 0016-7061 - p. 262 - 272.
    conservation agriculture - carbon sequestration - no-tillage - microbial biomass - density fractions - term changes - dynamics - impact - pools - stabilization
    Soil organic carbon (SOC) is a major attribute of soil quality that responds to land management activities which is also important in the regulation of global carbon (C) cycling. This study evaluated bulk soil C and nitrogen (N) contents and C and N dynamics in three soil organic matter (SOM) fractions separated by density. The study was based on three tillage systems on farmer managed experiments (conventional tillage (CT), ripping (RP), direct seeding (DS)) and adjacent natural forest (NF) in Haplic Arenosols (sandy) and Rhodic Ferralsols (clayey) of Zimbabwe. Carbon stocks were significantly larger in forests than tillage systems, being significantly lower in sandy soils (15 and 14 Mg C ha- 1) than clayey soils (23 and 21 Mg C ha- 1) at 0–10 and 10–30 cm respectively. Nitrogen content followed the same trend. At the 0–10 cm depth, SOC stocks increased under CT, RP and DS by 0.10, 0.24, 0.36 Mg ha- 1 yr- 1 and 0.76, 0.54, 0.10 Mg ha- 1 yr- 1 on sandy and clayey soils respectively over a four year period while N stocks decreased by 0.55, 0.40, 0.56 Mg ha- 1 and 0.63, 0.65, 0.55 Mg ha- 1 respectively. SOM fractions were dominated by mineral associated heavy fraction (MaHF) which accounted for 86–93% and 94–98% on sandy and clayey soils respectively. Tillage systems on sandy soils had the smallest average free light fraction (fLF) and occluded light fraction (oLF) C stocks (25.3 ± 1.3 g m- 2 and 7.3 ± 1.2 g m- 2) at 0–30 cm when compared with corresponding NF (58.4 ± 4 g m2 and 18.5 ± 1.0 g m- 2). Clayey soils, had the opposite, having all fLF C and N in tillage systems being higher (80.9 ± 12 g C m- 2 and 2.7 ± 0.4 g N m- 2) than NF (57.4 ± 2.0 g C m- 2 and 2.4 ± 0.3 g N m- 2). Results suggest that oLF and MaHF C and N are better protected under DS and RP where they are less vulnerable to mineralisation while fLF contributes more in CT. Thus, DS and RP can be important in maintaining and improving soil quality although their practicability can be hampered by unsupportive institutional frameworks. Under prevailing climatic and management conditions, improvement of residue retention could be a major factor that can distinguish the potential of different management practices for C sequestration. The exploitation of the benefits of RP or DS and the corresponding sustainability of systems need support for surface cover retention which should also be extended to conventional tillage
    Pushing the envelope? Maize production intensification and the role of cattle manure in recovery of degraded soils in smallholder farming areas of Zimbabwe
    Rusinamhodzi, L. ; Corbeels, M. ; Zingore, S. ; Nyamangara, J. ; Giller, K.E. - \ 2013
    Field Crops Research 147 (2013). - ISSN 0378-4290 - p. 40 - 53.
    repellent sandy soil - organic-matter - ecological intensification - conservation agriculture - fertility gradients - southern africa - management - systems - carbon - resource
    Soil fertility decline is a major constraint to crop productivity on smallholder farms in Africa. The objective of this study was to evaluate the long-term (up to nine years) impacts of nutrient management strategies and their local feasibility on crop productivity, soil fertility status and rainfall infiltration on two contrasting soil types and different prior management regimes in Murehwa, Zimbabwe. The nutrient management strategies employed in the study were: a control with no fertiliser, amendments of 100 kg N ha-1, 100 kg N + lime, three rates of manure application (5, 15 and 25 t ha-1) in combination with 100 kg N ha-1, and three rates of P fertiliser (10, 30 and 50 kg P ha-1) in combination with 100 kg N, 20 kg Ca, 5 kg Zn and 10 kg Mn ha-1. Maize grain yields in sandy soils did not respond to the sole application of 100 kg N ha-1; manure application had immediate and incremental benefits on crop yields on the sandy soils. A combination of 25 t ha-1 manure and 100 kg N gave the largest treatment yield of 9.3 t ha-1 on the homefield clay soils, 6.1 t ha-1 in the clay outfield, 7.6 t ha-1 in the homefield and 3.4 t ha-1 in the eighth season. Yields of the largest manure application on the sandy outfields were comparable to yields with 100 kg N in combination with 30 kg P, 20 kg Ca, 5 kg Zn and 10 kg Mn ha-1 in the homefields suggesting the need to target nutrients differently to different fields. Manure application improved rainfall infiltration in the clay soils from 21 to 31 mm h-1 but on the sandy soils the manure effect on infiltration was not significant. Despite the large manure applications, crop productivity and SOC build-up in the outfield sandy soils was small highlighting the difficulty to recover the fertility of degraded soils. The major cause of poor crop productivity on the degraded sandy soils despite the large additions of manure could not be ascertained. The current practice of allocating manure and fertiliser to fields closest to homesteads exacerbates land degradation in the sandy outfields and increases soil fertility gradients but results in the most harvest for the farm. On clay soils, manure may be targeted to outfields and mineral fertiliser to homefields to increase total crop productivity. Farmers who owned cattle in the study site can achieve high manure application rates on small plots, and manure application can be rotated according to crop sequences. Consistent application of manure in combination with mineral fertilisers can be an effective option to improve crop yield, SOC and moisture conservation under smallholder farming conditions. Combined manure and mineral fertiliser application can be adapted locally as a feasible entry point for ecological intensification in mixed crop–livestock systems.
    When yield gaps are poverty traps: The paradigm of ecological intensification in African smallholder agriculture
    Tittonell, P.A. ; Giller, K.E. - \ 2013
    Field Crops Research 143 (2013). - ISSN 0378-4290 - p. 76 - 90.
    soil fertility management - nutrient use efficiencies - resource use efficiency - western kenya - conservation agriculture - exploring diversity - semiarid tropics - different scales - farming systems - field-scale
    Yield gaps are pervasive in African smallholder agriculture, and are large for almost all crops in all regions. There is consensus that poor soil fertility and nutrient availability are the major biophysical limitations to agricultural production in the continent. We identify two major yield gaps: (1) the gap between actual yields (YA) and the water-limited yield potential (Yw), which is the maximum yield achievable under rainfed conditions without irrigation if soil water capture and storage is optimal and nutrient constraints are released, and (2) The gap between YA, and a locally attainable yield (YL) which corresponds to the water and nutrient-limited yields that can be measured in the most productive fields of resource endowed farmers in a community. Estimates of these two yield gaps are given for major crops, together with a framework for how yield gaps can be estimated in a pragmatic way for different farming systems. The paradigm of ecological intensification which focuses on yield potential, soil quality and precision agriculture is explored for the African context. Our analysis suggests that smallholder farmers are unable to benefit from the current yield gains offered by plant genetic improvement. In particular, continued cropping without sufficient inputs of nutrients and organic matter leads to localised but extensive soil degradation and renders many soils in a non-responsive state. The lack of immediate response to increased inputs of fertiliser and labour in such soils constitutes a chronic poverty trap for many smallholder farmers in Africa. This necessitates a rethink for development policy aimed to improve productivity and address problems of food insecurity.
    Medium-term impact of tillage and residue management on soil aggregate stability, soil carbon and crop productivity
    Paul, B.K. ; Vanlauwe, B. ; Ayuke, F. ; Gassner, A. ; Hoogmoed, M. ; Hurisso, T.T. ; Koala, S. ; Lelei, D. ; Ndabamenye, T. ; Six, J. ; Pulleman, M.M. - \ 2013
    Agriculture, Ecosystems and Environment 164 (2013)1. - ISSN 0167-8809 - p. 14 - 22.
    organic-matter dynamics - conservation agriculture - no-till - africa - systems - nitrogen - kenya - stabilization - protection - yields
    Conservation agriculture is widely promoted for soil conservation and crop productivity increase, although rigorous empirical evidence from sub-Saharan Africa is still limited. This study aimed to quantify the medium-term impact of tillage (conventional and reduced) and crop residue management (retention and removal) on soil and crop performance in a maize–soybean rotation. A replicated field trial was started in sub-humid Western Kenya in 2003, and measurements were taken from 2005 to 2008. Conventional tillage negatively affected soil aggregate stability when compared to reduced tillage, as indicated by lower mean weight diameter values upon wet sieving at 0–15 cm (PT <0.001). This suggests increased susceptibility to slaking and soil erosion. Tillage and residue management alone did not affect soil C contents after 11 cropping seasons, but when residue was incorporated by tillage, soil C was higher at 15–30 cm (PT*R = 0.037). Lack of treatment effects on the C content of different aggregate fractions indicated that reduced tillage and/or residue retention did not increase physical C protection. The weak residue effect on aggregate stability and soil C may be attributed to insufficient residue retention. Soybean grain yields tended to be suppressed under reduced tillage without residue retention, especially in wet seasons (PT*R = 0.070). Consequently, future research should establish, for different climatic zones and soil types, the critical minimum residue retention levels for soil conservation and crop productivity.
    Minimum tillage and vegetative barrier effects on crop yields in relation to soil water content in the Central Kenya highlands
    Guto, S.N. ; Ridder, N. de; Giller, K.E. ; Pypers, P. ; Vanlauwe, B. - \ 2012
    Field Crops Research 132 (2012). - ISSN 0378-4290 - p. 129 - 138.
    conservation agriculture - agroforestry system - napier grass - contour hedgerows - semiarid kenya - no-tillage - maize - erosion - competition - productivity
    The sub-humid zone of Central Kenya is water deficient due to regular intra-seasonal dry spells that constrain rain-fed crop production. A study was initiated to investigate the effects of minimum tillage and vegetative barriers on soil and water conservation and crop yield. There were two tillage practices; minimum and regular tillage and two vegetative barriers; 'leucaena' consisting of leguminous trees (Leucaena trichandra). and 'Napier' consisting of Napier grass (Pennisetum purpureum) in addition to a control without barriers. Maize and soybean crops were planted in rotation in the terraces between the barriers. Soil moisture content was measured near the barriers and at the centre of the terraces. Vegetative barriers impeded run-off and controlled soil loss. There was a positive linear relationship between soil loss and rainfall for Napier grass barriers. For leucaena barriers, soil loss increased quadratically with rainfall. At the onset of rainfall, soil water content increased for all tillage and barrier practices. With more rainfall, soil water content increased marginally without barriers while with barriers there was continued soil water build-up. At the end of the wet period and across tillage practice, the soil contained 43% more water near leucaena barriers compared with no barriers and 20% more at the centre of the terrace. For Napier barriers, the soil water content was 60% more near barriers and 30% more at the centre of the terrace. Without barriers, the soil water content was 10% more with regular rather than minimum tillage. At the cessation of rainfall, soil water declined in all tillage and barrier treatments. At the centre of the terraces and across barriers, soil water reduction compared with no barriers was 10% less for minimum tillage and 24% more for regular tillage. Nearer barriers, the soil water reduction (relative to regular tillage without barriers) for leucaena barriers was 56% less with minimum tillage and 77% less with regular tillage. Conversely with Napier barriers, there was stronger water reduction with minimum (116%) than regular tillage (102%). At the centre of the terraces and across vegetative barriers, the upper soil layers (60 cm) independent of tillage practice. In contrast, Napier barriers extracted more water from the upper end of the profile, especially with minimum tillage. Napier barriers with minimum tillage suppressed maize row-grain yields (relative to regular tillage without barriers) by 26% over a distance of 311 along the barrier crop interface. Maize yield suppression for Napier barriers with regular tillage was less pronounced (occurring over a distance of 1.5 m) and improved maize crop performance at the centre of the terraces increased overall row grain yields by 14% relative to regular tillage without barriers. Soybean yields with Napier barriers were suppressed over a distance of 0.5 m in the barrier crop interface. Maize and soybean yield suppression with leucaena barriers for the different tillage practices was less pronounced, and improved crop performance at the centre of terraces consistently compensated for any yield reductions at the barrier crop interface. Between tillage and barriers treatments, the degree of yield suppression was related to the water use pattern of the vegetative barriers, and more severe with Napier than with leucaena barriers, particularly with minimum tillage. A possible strategy for successful introduction of a combination of minimum tillage and the vegetative barriers into water deficient highland regions would include leucaena barriers with minimum tillage due to less competition for water between barriers and companion crops. Napier barriers with minimum tillage do not combine well due to strong competition for available water between the barriers and crops, even when intensely harvested.
    Assessing the impact of soil degradation on food production
    Bindraban, P.S. ; Velde, M. van der; Ye, L. ; Berg, M. van den; Materechera, S. ; Kiba, D.I. ; Tamene, L. ; Ragnarsdottir, K.V. ; Jongschaap, R.E.E. ; Hoogmoed, M. ; Hoogmoed, W.B. ; Beek, C.L. ; Lynden, G.W.J. van - \ 2012
    Current Opinion in Environmental Sustainability 4 (2012)5. - ISSN 1877-3435 - p. 478 - 488.
    conservation agriculture - carbon sequestration - land degradation - africa - erosion - yield - management - security - climate - trends
    Continuing soil degradation remains a serious threat to future food security. Yet, global soil degradation assessments are based on qualitative expert judgments or remotely sensed quantitative proxy values that suffice to raise awareness but are too coarse to identify appropriate sustainable land management interventions. Studies in China and Sub Saharan Africa illustrate the considerable impact of degradation on crop production but also point to the need for solutions dependent on location specific agro-ecological conditions and farming systems.The development of a comprehensive approach should be feasible to better assess both extent and impact of soil degradation interlinking various scales, based on production ecological approaches and remote sensing to allow disentangling natural and human induced causes of degradation. A shared common knowledge base cataloguing hard-won location-specific interventions is needed for successfully preventing or mitigating degradation
    Maize-grain legume intercropping is an attractive option for ecological intensification that reduces climatic risk for smallholder farmers in central Mozambique
    Rusinamhodzi, L. ; Corbeels, M. ; Nyamangara, J. ; Giller, K.E. - \ 2012
    Field Crops Research 136 (2012). - ISSN 0378-4290 - p. 12 - 22.
    soil fertility - conservation agriculture - nitrogen-fixation - resource capture - crop-rotation - systems - yield - cowpea - striga - decomposition
    Many farmers in central Mozambique intercrop maize with grain legumes as a means to improve food security and income. The objective of this study was to understand the farming system, and to evaluate the suitability of maize–legume intercropping to alleviate the biophysical and socio-economic constraints faced by smallholder farmers in Ruaca and Vunduzi villages, central Mozambique. To achieve this we characterised the farming systems and measured grain yields, rainfall infiltration, economic returns and acceptability of maize–legume intercrops under different N and P application rates. Two intercropping strategies were tested: (a) an additive design of within-row intercropping in which legume was intercropped with alternating hills of maize within the same row; maize plant population was the same as sole crop maize, and (b) a substitutive design with distinct alternating rows of maize and legume (local practice). Fertiliser treatments imposed on all treatments were: (i) no fertiliser, (ii) 20 kg P ha-1, (iii) 20 kg P ha-1 + 30 kg N ha-1, and (iv) 20 kg P ha-1 + 60 kg N ha-1. Intercrops were relatively more productive than the corresponding sole crops; land equivalent ratios (LER) for within-row intercropping ranged between 1.1 and 2.4, and between 1.0 and 1.9 for distinct-row intercropping. Average maize yield penalty for intercropping maize and pigeonpea in the within-row was small (8%) compared with 50% in the distinct-row design; average (season × fertiliser) sole maize yield was 3.2 t ha-1. Intercropping maize and cowpea in within-row led to maize yield loss of only 6%, whereas distinct-row intercropping reduced maize yield by 25% from 2.1 t ha-1 of sole maize (season × fertiliser). Cowpea yield was less affected by intercropping: sole cowpea had an average yield of 0.9 t ha-1, distinct-row intercropping (0.8 t ha-1) and the within-row intercropping yielded 0.9 t ha-1. Legumes were comparatively less affected by the long dry spells which were prevalent during the study period. Response to N and P fertiliser was weak due to poor rainfall distribution. In the third season, maize in rotation with pigeonpea and without N fertiliser application yielded 5.6 t ha-1, eight times more than continuous maize which was severely infested by striga (Striga asiatica) and yielded only 0.7 t ha-1. Rainfall infiltration increased from 6 mm h-1 to 22 mm h-1 with long-term maize–legume intercropping due to a combination of good quality biomass production which provided mulch combined with no tillage. Intercropping maize and pigeonpea was profitable with a rate of return of at least 343% over sole maize cropping.
    Trade-offs between biomass use and soil cover. The case of rice-based cropping systems in the lake Alaotra region of Madagascar
    Naudin, K. ; Scopel, E. ; Andriamandroso, A.L.H. ; Rakotosolofo, M. ; Andriamarosoa Ratsimbazafy, N.R.S. ; Rakotozandriny, J.N. ; Salgado, P. ; Giller, K.E. - \ 2012
    Experimental Agriculture 48 (2012)2. - ISSN 0014-4797 - p. 194 - 209.
    conservation agriculture - residue - nitrogen - tillage - water - management - erosion - quality - maize - crops
    Farmers in the Lake Alaotra region of Madagascar are currently evaluating a range of conservation agriculture (CA) cropping systems. Most of the expected agroecological functions of CA (weed control, erosion control and water retention) are related to the degree of soil cover. Under farmers’ conditions, the grain and biomass productivity of these systems is highly variable and the biomass is used for several purposes. In this study, we measured biomass production of cover crops and crops in farmers’ fields. Further, we derived relationships to predict the soil cover that can be generated for a particular quantity of mulch. We used these relationships to explore the variability of soil cover that can be generated in farmers’ fields, and to estimate howmuch of the biomass can be removed for use as livestock feed, while retaining sufficient soil cover. Three different kinds of cropping systems were investigated in 91 farmers’ fields. The first two cropping sequences were on the hillsides: (i) maize + pulse (Vigna unguiculata or Dolichos lablab) in year 1, followed by upland rice in year 2; (ii) the second crop sequence included several years of Stylosanthes guianensis followed by upland rice; (iii) the third crop sequence was in lowland paddy fields: Vicia villosa or D. lablab, which was followed by rice within the same year and repeated every year. The biomass available prior to rice sowing varied from 3.6 t ha-1 with S. guianensis to 7.3 t ha-1 with V. villosa. The relationship between the mulch quantity (M) and soil cover (C) was measured using digital imaging and was well described by the following equation: C = 1 - exp(-Am × M), where Am is an area-to-mass ratio with R2 > 0.99 in all cases. The calculated average soil cover varied from 56 to 97% for maize + V. unguiculata and V. villosa, respectively. In order to maintain 90% soil cover at rice sowing, the average amount of biomass of V. villosa that could be removed was at least 3 t ha-1 for three quarters of the fields. This quantity was less for other annual or biennial cropping systems. On average the V. villosa aboveground biomass contained 236 kg N ha-1. The study showed that for the conditions of farmers of Malagasy, the production and conservation of biomass is not always sufficient to fulfil all the above-cited agroecological functions of mulch. Inventory of the soil cover capacity for different types of mulch may help farmers to decide how much biomass they can remove from the field
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