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Vandamme E.,Catholic University of Leuven | Renkens M.,Catholic University of Leuven | Pypers P.,Catholic University of Leuven | Pypers P.,Tropical Soil Biology And Fertility Institute of CIAT | And 3 more authors.
Plant and Soil | Year: 2013

Background and aims: Incorporating soybean (Glycine max) genotypes with a high nitrogen fixation potential into cropping systems can sustainably improve the livelihoods of smallholder farmers in Western Kenya. Nitrogen fixation is, however, often constrained by low phosphorus (P) availability. The selection of soybean genotypes for increased P efficiency could help to overcome this problem. This study investigated the contribution of different root traits to variation in P efficiency among soybean genotypes. Methods: Eight genotypes were grown in a Ferralsol amended with suboptimal (low P) and optimal (high P) amounts of soluble P. Root hair growth was visualized by growing plants in a novel agar system where P intensity was buffered by Al2O3 nanoparticles. Results: In the pot trial, P uptake was unaffected among the genotypes at high P but differed about 2-fold at low P. The genotypes differed in P uptake efficiency but not in P utilization efficiency. Regression analysis and mechanistic modeling indicated that P uptake efficiencies were to a large extent related to root hair development (length and density) and, to a lower extent, to colonization by mycorrhizal fungi. Conclusion: Breeding for improved root hair development is a promising way to increase P uptake efficiency in soybean. © 2012 Springer Science+Business Media Dordrecht.


Vanlauwe B.,Tropical Soil Biology And Fertility Institute of CIAT | Kihara J.,Tropical Soil Biology And Fertility Institute of CIAT | Chivenge P.,University of California at Davis | Pypers P.,Tropical Soil Biology And Fertility Institute of CIAT | And 2 more authors.
Plant and Soil | Year: 2011

Traditionally, crop production in sub-Saharan Africa (SSA) depends primarily on mining soil nutrients. Integrated Soil Fertility Management (ISFM) is an approach for intensifying agriculture in SSA that aims at maximizing the agronomic efficiency (AE) of applied nutrient inputs. ISFM contains the following essential components: proper fertilizer management, use of improved varieties, the combined application of organic inputs and fertilizer, and adaptation of input application rates to within-farm soil fertility gradients where these are important. This paper evaluates, through meta-analysis, the impact of these components on the AE of fertilizer N (N-AE), defined as extra grain yield per kg fertilizer N applied, in maize-based systems in SSA. Since N-AE is low for excessive fertilizer N application rates or when fertilizer is applied on fertile, unresponsive soil, as was confirmed by scatter plots against control yields and fertilizer N application rates, such values were removed from the database in order to focus on and elucidate the more variable and complex responses under less than ideal conditions typical for SSA. Compared with local varieties, the use of hybrid maize varieties significantly increased N-AE values (17 and 26 kg (kg N)-1, respectively) with no differences observed between local and improved, open-pollinated varieties. Mixing fertilizer with manure or compost resulted in the highest N-AE values [36 kg (kg N)-1] while organic inputs of medium quality also showed significantly higher N-AE values compared with the sole fertilizer treatment but only at low organic input application rates (40 and 23 kg (kg N)-1, respectively). High quality organic inputs (Class I) and those with a high C-to-N ratio (Class III) or high lignin content (Class IV) did not affect N-AE values in comparison with the sole fertilizer treatment. Application of N fertilizer on infields resulted in significantly higher N-AE values [31 kg (kg N)-1] compared with the outfields [17 kg (kg N)-1]. The obtained information indicates that N-AE is amenable to improved management practices and that the various components embedded in the ISFM definition result in improvements in N-AE. © 2010 Springer Science+Business Media B.V.


Six L.,Catholic University of Leuven | Pypers P.,Tropical Soil Biology And Fertility Institute of CIAT | Degryse F.,University of Adelaide | Smolders E.,Catholic University of Leuven | Merckx R.,Catholic University of Leuven
Plant and Soil | Year: 2012

Background and aims: A soil test that samples nutrients only from fractions that are accessible to plants will predict availability and uptake more robustly than empirical tests. This can be tested by comparison of the isotope ratios (specific activity, SA) of the nutrient between plant and the soil extract. This study was set up to assess this requirement for the diffusive gradients in thin films technique (DGT), recently proposed as a soil P test, in comparison with conventional soil P tests viz. Olsen, Colwell, Bray-1, Mehlich-3, ammonium oxalate, anion exchange membranes (AEM) and 0. 01 M CaCl 2 solution. Methods: Maize (Zea mays L.) was grown in two P-deficient soils from western Kenya with contrasting P sorption characteristics, amended with a low and a high P rate and labelled with 33P. Results: The SA in the plant shoot corresponded with that of the extracts of the different soil tests, except for CaCl 2 and ammonium oxalate extracts, at the low P rate in the soil with low P sorption capacity, Teso soil. For the high P rate on this soil, differences in SA between maize shoot and soil test were small for all established soil tests, but significant for the Colwell, Bray-1, Mehlich-3 and AEM tests. The SA in the soil extracts was significantly smaller than that in the maize shoot for Sega the strongly P-sorbing soil at both P rates for all conventional tests, including AEM. This indicates that these tests extracted P from a pool that is not accessible to the plant. For the DGT test, however, there was no difference in SA between the maize shoot and the soil test, for any of the treatments. Conclusions: Most conventional soil tests can extract a fraction of P which is not available to maize. The DGT technique, however, only samples P from the plant-accessible pool. © 2012 Springer Science+Business Media B.V.


Gentile R.M.,University of California at Davis | Vanlauwe B.,Tropical Soil Biology And Fertility Institute of CIAT | Vanlauwe B.,International Institute Of Tropical Agriculture | Six J.,University of California at Davis | Six J.,ETH Zurich
Soil Biology and Biochemistry | Year: 2013

Soil organic matter is important to improve and sustain soil fertility in tropical agroecosystems. The combined use of organic residue and fertilizer inputs is advocated for its positive effects on short-term nutrient supply, but the effect of the integrated use on long-term stabilization of soil organic C and N is still unclear. We conducted a 1.5-y soil incubation experiment with maize (Zea mays) residue and urea fertilizer to examine the stabilization of C and N in four Sub-Saharan African soils differing in texture (sand, sandy loam, clay loam, and clay). The inputs were enriched with 13C and 15N in a mirror-labelling design to trace the fate of residue-C and N, and fertilizer-N in combination. We hypothesized that combining inputs would enhance the stabilization of C and N relative to either input alone across a range of soil textures. The treatments were destructively sampled after 0.25, 0.5, and 1.5y to assess input-derived C and N stabilization in soil macro- and microaggregate fractions. The combination treatment had a significant but small (2% of residue-applied C) increase in residue-C stabilized in the total soil after0.25y, but this increase did not persist after 0.5 and 1.5y. While combining residue and fertilizer decreased the amount of residue-N stabilized within 53- to 2000-μm sized soil aggregates (e.g., 7% less at1.5y), it increased the stabilization of fertilizer-N at all sampling times (e.g., 20% more at 1.5y). The increased amount of fertilizer-N stabilized was significantly greater than the amount of residue-N lost in the combined input treatments in the three finer textured soils at 1.5y, indicating an interactive increase in the stabilization of new N. Our results indicate that combining residue with fertilizer inputs can increase the short-term stabilization of N, which has the potential to improve soil fertility. However, benefits to N stabilization from combining organic residues and fertilizer seem to be less in coarser-textured soils. © 2013 Elsevier Ltd.


Rufino M.C.,Wageningen University | Dury J.,Wageningen University | Tittonell P.,Wageningen University | van Wijk M.T.,Wageningen University | And 5 more authors.
Agricultural Systems | Year: 2011

In communal areas of NE Zimbabwe, feed resources are collectively managed, with herds grazing on grasslands during the rainy season and mainly on crop residues during the dry season, which creates interactions between farmers and competition for organic resources. Addition of crop residues or animal manure is needed to sustain agricultural production on inherently poor soils. Objectives of this study were to assess the effect of village-level interactions on carbon and nutrient flows, and to explore their impact on the long-term productivity of different farm types under climate variability. Crop and cattle management data collected in Murewa Communal area, NE Zimbabwe was used together with a dynamic farm-scale simulation model (NUANCES-FARMSIM) to simulate village-level interactions. Simulations showed that grasslands support most cattle feed intake (c. 75%), and that crop residues produced by non-cattle farmers sustain about 30% of the dry season feed intake. Removal of crop residues (0.3-0.4tCha-1yr-1) from fields of non-cattle farmers resulted in a long-term decrease in crop yields. No-access to crop residues of non-cattle farmers increased soil C modestly and improved yields in the long-term, but not enough to meet household energy requirements. Harvest of grain and removal of most crop residues by grazing cattle caused a long-term decline in soil C stocks for all farm types. The smallest decrease (-0.5tCha-1) was observed for most fertile fields of cattle farmers, who manure their fields. Cattle farmers needed to access 4-10ha of grassland to apply 3t of manure ha-1yr-1. Rainfall variability intensifies crop-livestock interactions increasing competition for biomass to feed livestock (short-term effect) or to rehabilitate soils (long-term effect). Prolonged dry seasons and low availability of crop residues may lead to cattle losses, with negative impact in turn on availability of draught power, affecting area under cultivation in consecutive seasons until farmers re-stock. Increasing mineral fertiliser use concurrently with keeping crop residues in fertile fields and allocating manure to poor fields appears to be a promising strategy to boost crop and cattle productivity at village level. The likelihood of this scenario being implemented depends on availability of fertilisers and decision of farmers to invest in rehabilitating soils to obtain benefits in the long-term. Adaptation options cannot be blind to what occurs beyond field and farm level, because otherwise recommendations from research and development do not fit the local conditions and farmers tend to ignore them. © 2010 Elsevier Ltd.


Pauli N.,University of Western Australia | Pauli N.,Tropical Soil Biology And Fertility Institute of CIAT | Barrios E.,Tropical Soil Biology And Fertility Institute of CIAT | Conacher A.J.,University of Western Australia | Oberthur T.,Land Use Project
Applied Soil Ecology | Year: 2011

Smallholder agroforestry systems often incorporate features that are associated with abundant, diverse soil macrofauna populations. This study sampled soil macrofauna communities across four major land uses present within agricultural landscapes where the Quesungual Slash-and-Mulch Agroforestry System (QSMAS) has been increasingly adopted by smallholder farmers in western Honduras. The four land uses were: secondary forest (F), agroforestry plots of less than two years of age (AF<2), agroforestry plots of more than 10 years of age (AF>10), and silvipastoral fields (SP). Transect-based sampling of soil macrofauna using the standard Tropical Soil Biology and Fertility Institute (TSBF) method was employed in both the dry season and wet season. All four land uses sampled in this study harboured diverse, abundant and highly variable soil macrofauna populations. In the dry season, total density of soil macrofauna ranged from 1265±308individualsm-2 in F sites to 1924±436individualsm-2 in AF<2 sites. In the wet season, total density ranged from 907±294individualsm-2 in F, to 1637±358individualsm-2 in AF<2. Biomass values followed a similar pattern, ranging from 4.3±1.1gm-2 to 24.8±8.2gm-2 in the dry season and from 13.1±3.0gm-2 to 41.9±11.1gm-2 in the wet season. In order of decreasing strength of statistical relationship, soil depth, land use and season were all related to some aspects of soil macrofauna density, biomass and community composition. At a broad functional group level, soil macrofauna community composition was very similar across all four land uses. The results suggest that the agricultural practices associated with the 'Quesungual' agroforestry system may promote a relatively abundant, diverse soil macrofauna community. The presence of an abundant soil macrofauna community may have important effects on aspects of soil quality that are particularly important to resource-limited smallholder farmers. © 2010 Elsevier B.V.


Cobo J.G.,University of Hohenheim | Cobo J.G.,Tropical Soil Biology And Fertility Institute of CIAT | Dercon G.,University of Hohenheim | Cadisch G.,University of Hohenheim
Agriculture, Ecosystems and Environment | Year: 2010

Nutrient balances are useful tools as indicators of potential land degradation and for optimizing nutrient use, and are thus highly relevant in the African context. A comprehensive literature review on nutrient balances in Africa was carried out to illustrate the main approaches, challenges, and progress, with emphasis on issues of scale. The review showed nutrient balances being widely used across the continent. The collected dataset from 57 peer-reviewed studies indicated, however, that most of the balances were calculated at plot and farm scale, and generated in East Africa. Data confirmed the expected trend of negative balances in the continent for nitrogen and potassium, where >75% of selected studies had mean values below zero. For phosphorus only 56% of studies showed negative mean balances. Several cases with positive nutrient balances indicated that soil nutrient mining cannot be generalized across the continent. Land use systems of wealthier farmers mostly presented higher nitrogen and phosphorus balances than systems of poorer farmers (p < 0.001). Plots located close to homesteads also usually presented higher balances than plots located relatively farther away (p < 0.05). Partial nutrient balances were significantly higher (p < 0.001) than full balances calculated for the same systems, but the later carried more uncertainties. The change in magnitude of nutrient balances from plot to continental level did not show any noticeable trend, which challenges prevailing assumptions that an increasing trend exists. However, methodological differences made a proper inter-scale comparison of results difficult. Actually, the review illustrated the high diversity of methods used to calculate nutrient balances and highlighted the main pit-falls, especially when nutrient flows and balances were scaled-up. Major generic problems were the arbitrary inclusion/exclusion of flows from the calculations, short evaluation periods, and difficulties on setting of spatial-temporal boundaries, inclusion of lateral flows, and linking the balances to soil nutrient stocks. The need for properly describing the methods used and reporting the estimates (i.e. appropriate units and measure of variability and error) were also highlighted. Main challenges during scaling-up were related to the type of aggregation and internalization of nutrient flows, as well as issues of non-linearity, and spatial variability, resolution and extent, which have not been properly addressed yet. In fact, gathered information showed that despite some few initiatives, scaling-up methods are still incipient. Lastly, promising technologies and recommendations to deal with these challenges were presented to assist in future research on nutrient balances at different spatial scales in Africa and worldwide. © 2009 Elsevier B.V. All rights reserved.


Isaac M.E.,Montpellier SupAgro | Isaac M.E.,University of Toronto | Harmand J.-M.,Montpellier SupAgro | Lesueur D.,Montpellier SupAgro | And 2 more authors.
Forest Ecology and Management | Year: 2011

Acacia senegal, an important leguminous tree in arid and semi-arid environments, has shown promise as a multipurpose species, including gum production and soil fertility improvement, linked with N2-fixation capabilities. Of particular interest are ontogenetic and edaphic effects on A. senegal performance in natural populations. Our research objectives were to investigate the effect of tree age and site phosphorus conditions on (1) tree N2-fixation and (2) soil N and C dynamics in natural stands of A. senegal var. senegal, Baringo District, in the Rift Valley, Kenya. Sites consisted of A. senegal saplings (9 months) and mature A. senegal trees (7 years) along an edaphic gradient of soil P availability. A single-tree neighborhood approach was employed using a two by two factorial design: site conditions [high and low soil P contents] and tree age class [juvenile and mature]. Soil (N and C pools and fluxes) and plant metrics were quantified. A soil transfer experiment was also employed to confirm age and site effects on soil N mineralization. On the high soil P site, A. senegal had significantly lower foliar (15N levels than neighboring non-leguminous species (Balanites aegyptiaca), while foliar δ15N values in A. senegal on the low P site exhibited no significant difference with our reference plant, B. aegyptiaca. Across P sites, B. aegyptiaca had similar foliar δ15N values. These results indicate that the rate of N2-fixation of A. senegal trees, as determined with foliar 15N natural abundance methodology, increased with increasing soil P availability in these natural populations. However, N2-fixation rates declined with age. Although soil texture and soil CO2 efflux did not differ between sites or across ages, soils under mature A. senegal at the high P site exhibited significantly greater total N content and total C content in comparison to soils at the low P site and under juvenile plants. Furthermore, under mature A. senegal trees, soil N mineralization rates were significantly greater as compared to under saplings. Soil transplants confirmed that soil microbial activity may be stimulated under mature trees as N mineralization rates were 2-3 fold greater compared to under A. senegal saplings. Our findings suggest that tree age and soil P availability are important factors in the nitrogen budget of natural populations of A. senegal, determining N2-fixation rates, and potentially influencing soil total N and C pools and soil mineral N. This study provides information regarding the adaptation of A. senegal under differing edaphic conditions thus increasing accuracy of management support for A. senegal populations as productive agroforests. © 2010 Elsevier B.V.


Pypers P.,Tropical Soil Biology And Fertility Institute of CIAT | Sanginga J.-M.,Centro Internacional Of Agricultura Tropical | Kasereka B.,Centro Internacional Of Agricultura Tropical | Walangululu M.,Catholic University of Bukavu | Vanlauwe B.,Tropical Soil Biology And Fertility Institute of CIAT
Field Crops Research | Year: 2011

Smallholder farmers in sub-Saharan Africa are confronted by low productivity and limited investment capacity in nutrient inputs. Integrated soil fertility management (ISFM) aims at increased productivity through the combined use of improved germplasm, judicious fertilizer application and organic matter management, adapted to the local farming conditions. We hypothesize that the application of these different ISFM components can result in significant increases in productivity and economic benefits of cassava-legume intercropping systems. Participatory demonstration trials were conducted in the highlands of Sud-Kivu, DR Congo with 12 farmer groups during 3 seasons. Treatments included the farmers' common practice (local common bean and cassava varieties, seed broadcast and manure addition) and sequentially added ISFM components: improved bean and cassava germplasm, modified crop arrangements, compound NPK fertilizer application and alternative legume species (groundnut or soybean). The use of improved germplasm did not result in yield increases without simultaneous implementation of other ISFM components. Modifying the crop arrangement by planting cassava at 2m between rows and 0.5m within the row, intercropped with four legume lines, increased bean yields during the first season and permits a second bean intercrop, which can increase total legume production by up to 1tha -1 and result in an additional revenue of almost 1000USDha -1. Crop arrangement or a second legume intercrop did not affect cassava storage root yields. Fertilizer application increased both legume and cassava yield, and net revenue by 400-700USDha -1 with a marginal rate of return of 1.6-2.7. Replacing the common bean intercrop by groundnut increased net revenue by 200-400USDha -1 partly because of the higher market value of the grains, but mostly due to a positive effect on cassava storage root yield. Soybean affected cassava yields negatively because of its high biomass production and long maturity period; modifications are needed to integrate a soybean intercrop into the system. The findings demonstrate the large potential of ISFM to increase productivity in cassava-legume systems in the Central-African highlands. Benefits were, however, not observed in all study sites. In poor soils, productivity increases were variable or absent, and soil amendments are required. A better understanding of the conditions under which positive effects occur can enable better targeting and local adaptation of the technologies. © 2010 Elsevier B.V.


Tittonell P.,Wageningen University | Tittonell P.,CIRAD - Agricultural Research for Development | Corbeels M.,CIRAD - Agricultural Research for Development | Corbeels M.,Tropical Soil Biology And Fertility Institute of CIAT | And 2 more authors.
European Journal of Agronomy | Year: 2010

Resources for crop production are often scarce in smallholder farming systems in the tropics, particularly in sub-Saharan Africa (SSA). Decisions on the allocation of such resources are often made at farm rather than at field plot scale. To handle the uncertainty caused by both lack of data and imperfect knowledge inherent to these agricultural systems, we developed a dynamic summary model of the soil-crop system that captures essential interactions determining the short- and long-term crop productivity, while keeping a degree of simplicity that allows its parameterisation, use and dissemination in the tropics. Generic, summary functions describing crop productivity may suffice for addressing questions concerning trade-offs on resource allocation at farm scale. Such functions can be derived from empirical (historical) data or, when they involve potential or water-limited crop yields, can be generated using process-based, detailed crop simulation models. This paper describes the approach to simulating crop productivity implemented in the model FIELD (Field-scale Interactions, use Efficiencies and Long-Term soil fertility Development), based on the availability of light, water, nitrogen, phosphorus and potassium, and the interactions between these factors. We describe how these interactions are simulated and use examples from case studies in African farming systems to illustrate the use of detailed crop models to generate summary functions and the ability of FIELD to capture long-term trends in soil C and crop yields, crop responses to applied nutrients across heterogeneous smallholder farms and the implications of overlooking the effects of intra-seasonal rainfall variability in the model. An example is presented that evaluates the sensitivity of the model to resource allocation decisions when operating (linked to livestock and household models) at farm scale. Further, we discuss the assessment of model performance, going beyond the calculation of simple statistics to compare simulated and observed results to include broader criteria such as model applicability. In data-scarce environments such as SSA, uncertainty in parameter values constrains the performance of detailed process-based models, often forcing model users to 'guess' (or set to default values) parameters that are seldom measured in practice. The choice of model depends on its suitability and appropriateness to analyse the relevant scale for the question addressed. Simpler yet dynamic models of the various subsystems (crop, soil, livestock, manure) may prove more robust than detailed, process-based models when analysing farm scale questions on system design and resource allocation in SSA. © 2009 Elsevier B.V. All rights reserved.

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