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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    The effect of developmental nutrition on life span and fecundity depends on the adult reproductive environment in Drosophila melanogaster
    May, C.M. ; Doroszuk, A. ; Zwaan, B.J. - \ 2015
    Ecology and Evolution 5 (2015)6. - ISSN 2045-7758 - p. 1156 - 1168.
    thrifty phenotype hypothesis - ischemic-heart-disease - dietary restriction - larval nutrition - caenorhabditis-elegans - resource-allocation - prenatal exposure - history evolution - food limitation - body-size
    Both developmental nutrition and adult nutrition affect life-history traits; however, little is known about whether the effect of developmental nutrition depends on the adult environment experienced. We used the fruit fly to determine whether life-history traits, particularly life span and fecundity, are affected by developmental nutrition, and whether this depends on the extent to which the adult environment allows females to realize their full reproductive potential. We raised flies on three different developmental food levels containing increasing amounts of yeast and sugar: poor, control, and rich. We found that development on poor or rich larval food resulted in several life-history phenotypes indicative of suboptimal conditions, including increased developmental time, and, for poor food, decreased adult weight. However, development on poor larval food actually increased adult virgin life span. In addition, we manipulated the reproductive potential of the adult environment by adding yeast or yeast and a male. This manipulation interacted with larval food to determine adult fecundity. Specifically, under two adult conditions, flies raised on poor larval food had higher reproduction at certain ages – when singly mated this occurred early in life and when continuously mated with yeast this occurred during midlife. We show that poor larval food is not necessarily detrimental to key adult life-history traits, but does exert an adult environment-dependent effect, especially by affecting virgin life span and altering adult patterns of reproductive investment. Our findings are relevant because (1) they may explain differences between published studies on nutritional effects on life-history traits; (2) they indicate that optimal nutritional conditions are likely to be different for larvae and adults, potentially reflecting evolutionary history; and (3) they urge for the incorporation of developmental nutritional conditions into the central life-history concept of resource acquisition and allocation
    On the fate of seasonally plastic traits in a rainforest butterfly under relaxed selection
    Oostra, V. ; Brakefield, P.M. ; Hiltemann, Y. ; Zwaan, B.J. ; Brattström, O. - \ 2014
    Ecology and Evolution 4 (2014)13. - ISSN 2045-7758 - p. 2654 - 2667.
    sexual size dimorphism - bicyclus-anynana - phenotypic plasticity - reaction norms - life-history - evolutionary significance - artificial selection - geographic-variation - resource-allocation - thermal plasticity
    Many organisms display phenotypic plasticity as adaptation to seasonal environmental fluctuations. Often, such seasonal responses entails plasticity of a whole suite of morphological and life-history traits that together contribute to the adaptive phenotypes in the alternative environments. While phenotypic plasticity in general is a well-studied phenomenon, little is known about the evolutionary fate of plastic responses if natural selection on plasticity is relaxed. Here, we study whether the presumed ancestral seasonal plasticity of the rainforest butterfly Bicyclus sanaos (Fabricius, 1793) is still retained despite the fact that this species inhabits an environmentally stable habitat. Being exposed to an atypical range of temperatures in the laboratory revealed hidden reaction norms for several traits, including wing pattern. In contrast, reproductive body allocation has lost the plastic response. In the savannah butterfly, B. anynana (Butler, 1879), these traits show strong developmental plasticity as an adaptation to the contrasting environments of its seasonal habitat and they are coordinated via a common developmental hormonal system. Our results for B. sanaos indicate that such integration of plastic traits – as a result of past selection on expressing a coordinated environmental response – can be broken when the optimal reaction norms for those traits diverge in a new environment
    The 'One cow per poor family' programme: Current and potential fodder availability within smallholder farming systems in southwest Rwanda
    Klapwijk, C.J. ; Bucagu, C. ; Wijk, M.T. van; Udo, H.M.J. ; Vanlauwe, B. ; Munyanziza, E. ; Giller, K.E. - \ 2014
    Agricultural Systems 131 (2014). - ISSN 0308-521X - p. 11 - 22.
    soil fertility management - exploring diversity - resource-allocation - central highlands - western kenya - napier grass - agroforestry - productivity - variability - growth
    Livestock is an essential component of smallholder farming systems in the East African highlands. The ‘One cow per poor family’ programme was initiated in Rwanda as part of a poverty alleviation strategy, aiming to increase the livestock population. A four month-study was conducted in Umurera village (Simbi sector), southern Rwanda with the objectives to (1) quantify the on-farm fodder availability, (2) quantify the amount and quality of fodder on offer to livestock, (3) analyse potential fodder availability under five future scenarios and (4) evaluate the implications and feasibility of the programme. Farmers’ surveys, measurements of field sizes, together with daily measurements of fodder on offer, milk production and fodder refusals were conducted. Feeds used were diverse, comprising grasses (53%), banana plant parts (25%), residues of several crops (9%) and other plants (10%). Herbs collected from valley-bottoms, uncultivated grasses and crop residues were predominant fodder types on poorer (Resource group 1 – RG1) farms while Pennisetum and Calliandra were predominant fodder types for moderate (RG2) and better resource endowed (RG3) farms. The amount of fodder on offer for cattle ranged from 20 to 179 kg fresh weight animal-1 day-1 (9–47 kg DM). The milk yield ranged between 1.3 and 4.6 L day-1. The amount of Pennisetum and Calliandra fodder available decreased in the dry season with a concomitant increase in reliance on banana leaves and pseudo-stems. The poorest farmers (RG1) were not able to feed a local cow under all scenarios. RG2 farmers can sustain a local cow during both seasons when using all possible fodder resources, but can sustain a European cow under just two scenarios during the rainy season. RG3 farmers can feed a European cow during the rainy season under all scenarios and for four scenarios during the dry season. We conclude that the ‘One cow per poor family’ programme needs to be adjusted to increase its effectiveness. Our main recommendations are to shift to livestock that require less fodder, for example local cattle or small ruminants such as goats.
    Can we define the term 'farming systems'? A question of scale : Guest Editorial
    Giller, K.E. - \ 2013
    Outlook on Agriculture 42 (2013)3. - ISSN 0030-7270 - p. 149 - 153.
    soil fertility management - smallholder farms - exploring diversity - resource-allocation - western kenya - land-use - variability - methodology - space
    Soil heterogeneity and soil fertility gradients in smallholder agricultural systems of the east african highlands
    Tittonell, P.A. ; Muriuki, A. ; Klapwijk, C.J. ; Shepherd, K.D. ; Coe, R. ; Vanlauwe, B. - \ 2013
    Soil Science Society of America Journal 77 (2013)2. - ISSN 0361-5995 - p. 525 - 538.
    western kenya - resource-allocation - organic-matter - management - maize - variability - quality - productivity - indicators - tropics
    Heterogeneity in soil fertility in these smallholder systems is caused by both inherent soil-landscape and human-induced variability across farms differing in resources and practices. Interventions to address the problem of poor soil fertility in Africa must be designed to target such diversity and spatially heterogeneity. Data on soil management and soil fertility from six districts in Kenya and Uganda were gathered to understand the determinants of soil heterogeneity within farms. Analysis of the variance of soil fertility indicators across 250 randomly selected farms (i.e., 2607 fields), using a mixed model that considered site, sampling frame, farm type, and field as random terms, revealed that the variation in soil organic C (6.5–27.7 g kg-1), total N (0.6–3.0 g kg-1), and available P (0.9–27 mg kg-1) was mostly related to differences in the inherent properties of the soils across sites (50 to 60% of total variance). Exchangeable K+ (0.1–1.1 cmol(+) kg-1), Ca2+ (1.5–14.5 cmol(+) kg-1), Mg2+ (0.6–3.7 cmol(+) kg-1), and pH (5.1–6.9) exhibited larger residual variability associated with field-to-field differences within farms (30 to 50%). Soil fertility indicators decreased significantly with increasing distance from the homesteads. When this variable was included in the model, the unexplained residual variances—associated with soil heterogeneity within farms—were 38% for soil C; 32% for total N; 49% for available P; 56, 49, and 38% for exchangeable K+, Ca2+ and Mg2+, respectively; and 49% for the pH. In allocating nutrient resources, farmers prioritized fields they perceived as most fertile, reinforcing soil heterogeneity. Categorization of fields within a farm with respect to distance from the homestead, and soil fertility classes as perceived by farmers, were identified as entry points to target soil fertility recommendations to easily recognizable, distinct entities.
    Managing Tephrosia mulch and fertilizer to enhance coffee productivity on smallholder farms in the Eastern African Highlands
    Bucagu, C. ; Vanlauwe, B. ; Giller, K.E. - \ 2013
    European Journal of Agronomy 48 (2013). - ISSN 1161-0301 - p. 19 - 29.
    resource-allocation - nitrogen release - cropping systems - improved fallows - bukoba district - western kenya - cover crops - decomposition - variability - management
    In Maraba, Southwest Rwanda, coffee productivity is constrained by poor soil fertility and lack of organic mulch. We investigated the potential to produce mulch by growing Tephrosia vogelii either intercropped with smallholder coffee or in arable fields o
    Interactive effects of mechanical stress, sand burial and defoliation on growth and mechanical properties in Cynanchum komarovii
    Xu, L. ; Yu, F.H. ; Werger, M. ; Dong, M. ; Anten, N.P.R. - \ 2013
    Plant Biology 15 (2013)1. - ISSN 1435-8603 - p. 126 - 134.
    biomass allocation - resource-allocation - plant-response - lateral shade - gas-exchange - wind speeds - stem - thigmomorphogenesis - stimulation - tolerance
    In drylands, wind, sand burial and grazing are three important factors affecting growth and mechanical properties of plants, but their interactive effects have not yet been investigated. Plants of the semi-shrub Cynanchum komarovii, common in semi-arid parts of NE Asia, were subjected to brushing, burial and defoliation. We measured biomass allocation and relative increment rates of dry mass (RGRm), height (RGRh) and basal diameter (RGRd). We also measured the stem mechanical properties, Young’s modulus (E), second moment of area (I), flexural stiffness (EI) and breaking stress (sb), and scaled these traits to the whole-plant level to determine the maximum lateral force (Flateral) and the buckling safety factor (BSF). Brushing increased RGRm; neither burial nor defoliation independently affected RGRm, but together they reduced it. Among buried plants, brushing positively affected stem rigidity and strength through increasing RGRd, E, I and EI, and at whole plant level this resulted in a larger BSF and Flateral. However, among unburied plants this pattern was not observed. Our results thus show that effects of mechanical stress and grazing on plants can be strongly modified by burial, and these interactions should be taken into account when considering adaptive significance of plant mechanical traits in drylands.
    Strict mast fruiting for a tropical dipterocarp tree: a demographic cost–benefit analysis of delayed reproduction and seed predation
    Visser, M.D. ; Jongejans, E. ; Breugel, M. van; Zuidema, P.A. ; Chen, Y.Y. ; Kassim, A.R. ; Kroon, H. de - \ 2011
    Journal of Ecology 99 (2011)4. - ISSN 0022-0477 - p. 1033 - 1044.
    rain-forest - evolutionary ecology - spatial-patterns - resource-allocation - woody-plants - el-nino - recruitment - dispersal - dynamics - impact
    1. Masting, the production of large seed crops at intervals of several years, is a reproductive adaptation displayed by many tree species. The predator satiation hypothesis predicts that starvation of seed predators between mast years and satiation during mast years decreases seed predation and thus enhances tree regeneration. 2. Mast fruiting comes at demographic costs such as missed reproduction opportunities and increased density-dependence of recruits, but it remains unknown if predator satiation constitutes a sufficiently large benefit for masting to evolve as a viable life-history strategy. So far, no studies have quantified the net fitness consequences of masting. 3. Using a long-term demographic data set of the dipterocarp Shorea leprosula in a Malaysian forest, we constructed stochastic matrix population models and performed a demographic cost–benefit analysis. 4. For observed values of mast frequency and seed predation rates, we show that strict masting strongly increases fitness compared with fruiting annually. Model results also show that the demographic costs of mast fruiting are very low compared to the demographic losses due to seed predation in a scenario of annual fruiting. Finally, we find that mast fruiting would still be selected for even at low levels of seed predation and when including additional costs such as decreased adult growth rates, limiting crop size and density-dependent seedling survival. 5. Synthesis. Our results are consistent with the predictions of the predator satiation hypothesis: mast fruiting increases fitness for a range of seed predation levels. Under seed predation pressure annually fruiting species are at a strong disadvantage and as a result a mast fruiting strategy may swiftly confer a fitness advantage. Our study shows that demographic modelling allows the weighing of fitness benefits and costs of life-history phenomena such as strict masting.
    Communicating complexity: Integrated assessment of trade-offs concerning soil fertility management within African farming systems to support innovation and development
    Giller, K.E. ; Tittonell, P.A. ; Rufino, M.C. ; Wijk, M.T. van; Zingore, S. ; Mapfumo, P. ; Adjei-Nsiah, S. ; Herrero, M. ; Chikowo, R. ; Corbeels, M. ; Rowe, E.C. ; Baijukya, F.P. ; Mwijage, A. ; Smith, J. ; Yeboah, E. ; Burg, W.J. van der; Sanogo, O. ; Misiko, M. ; Ridder, N. de; Karanja, S. ; Kaizzi, C.K. ; K'ungu, J. ; Mwale, M. ; Nwaga, D. ; Pacini, C. ; Vanlauwe, B. - \ 2011
    Agricultural Systems 104 (2011)2. - ISSN 0308-521X - p. 191 - 203.
    nutrient use efficiencies - crop-livestock systems - western kenya - smallholder farms - land-use - southern mali - cycling efficiencies - exploring diversity - resource-allocation - dynamics
    African farming systems are highly heterogeneous: between agroecological and socioeconomic environments, in the wide variability in farmers’ resource endowments and in farm management. This means that single solutions (or ‘silver bullets’) for improving farm productivity do not exist. Yet to date few approaches to understand constraints and explore options for change have tackled the bewildering complexity of African farming systems. In this paper we describe the Nutrient Use in Animal and Cropping systems – Efficiencies and Scales (NUANCES) framework. NUANCES offers a structured approach to unravel and understand the complexity of African farming to identify what we term ‘best-fit’ technologies – technologies targeted to specific types of farmers and to specific niches within their farms. The NUANCES framework is not ‘just another computer model’! We combine the tools of systems analysis and experimentation, detailed field observations and surveys, incorporate expert knowledge (local knowledge and results of research), generate databases, and apply simulation models to analyse performance of farms, and the impacts of introducing new technologies. We have analysed and described complexity of farming systems, their external drivers and some of the mechanisms that result in (in)efficient use of scarce resources. Studying sites across sub-Saharan Africa has provided insights in the trajectories of change in farming systems in response to population growth, economic conditions and climate variability (cycles of drier and wetter years) and climate change. In regions where human population is dense and land scarce, farm typologies have proven useful to target technologies between farmers of different production objectives and resource endowment (notably in terms of land, labour and capacity for investment). In such regions we could categorise types of fields on the basis of their responsiveness to soil improving technologies along soil fertility gradients, relying on local indicators to differentiate those that may be managed through ‘maintenance fertilization’ from fields that are highly-responsive to fertilizers and fields that require rehabilitation before yields can improved. Where human population pressure on the land is less intense, farm and field types are harder to discern, without clear patterns. Nutrient cycling through livestock is in principle not efficient for increasing food production due to increased nutrient losses, but is attractive for farmers due to the multiple functions of livestock. We identified trade-offs between income generation, soil conservation and community agreements through optimising concurrent objectives at farm and village levels. These examples show that future analyses must focus at farm and farming system level and not at the level of individual fields to achieve appropriate targeting of technologies – both between locations and between farms at any given location. The approach for integrated assessment described here can be used ex ante to explore the potential of best-fit technologies and the ways they can be best combined at farm level. The dynamic and integrated nature of the framework allows the impact of changes in external drivers such as climate change or development policy to be analysed. Fundamental questions for integrated analysis relate to the site-specific knowledge and the simplification of processes required to integrate and move from one level to the next. Keywords: Crop–livestock systems; Soil fertility; Smallholders; Farm types; Simulation modelling
    Integrated soil fertility management: Operational definition and consequences for implementation and dissemination
    Vanlauwe, B. ; Bationo, A. ; Chianu, J. ; Giller, K.E. ; Merckx, R. ; Mokwunye, U. ; Ohiokpehai, O. ; Pypers, P. ; Tabo, R. ; Shepherd, K.D. ; Smaling, E.M.A. ; Woomer, P.L. ; Sanginga, N. - \ 2010
    Outlook on Agriculture 39 (2010)1. - ISSN 0030-7270 - p. 17 - 24.
    smallholder farms - western kenya - exploring diversity - resource-allocation - nutrient flows - variability - tropics - maize
    Traditional farming systems in Sub-Saharan Africa depend primarily on mining soil nutrients. The African green revolution aims to intensify agriculture through the dissemination of integrated soil fertility management (ISFM). This paper develops a robust and operational definition of ISFM based on detailed knowledge of African farming systems and their inherent variability and of the optimal use of nutrients. The authors define ISFM as a set of soil fertility 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, aimed at maximizing agronomic use efficiency of the applied nutrients and improving crop productivity. All inputs need to be managed in accordance with sound agronomic principles. The integration of ISFM practices into farming systems is illustrated with the dual-purpose grain legume-maize rotations in the savannas and fertilizer micro-dosing in the Sahel. Finally, the dissemination of ISFM practices is discussed
    Multiple growth-correlated life history traits estimated simultaneously in indivuals
    Mollet, F.M. ; Ernande, B. ; Brunel, T.P.A. ; Rijnsdorp, A.D. - \ 2010
    Oikos 119 (2010)1. - ISSN 0030-1299 - p. 10 - 26.
    north-sea plaice - pleuronectes-platessa l - herring clupea-harengus - evolving fish stocks - indeterminate growth - back-calculation - somatic growth - reaction norms - resource-allocation - arctica-islandica
    We present a new methodology to estimate rates of energy acquisition, maintenance, reproductive investment and the onset of maturation (four-trait estimation) by fitting an energy allocation model to individual growth trajectories. The accuracy and precision of the method is evaluated on simulated growth trajectories. In the deterministic case, all life history parameters are well estimated with negligible bias over realistic parameter ranges. Adding environmental variability reduces precision, causes the maintenance and reproductive investment to be confounded with a negative error correlation, and tends, if strong, to result in an underestimation of the energy acquisition and maintenance and an overestimation of the age and size at the onset of maturation. Assuming a priori incorrect allometric scaling exponents also leads to a general but fairly predictable bias. To avoid confounding in applications we propose to assume a constant maintenance (three-trait estimation), which can be obtained by fitting reproductive investment simultaneously to size at age on population data. The results become qualitatively more robust but the improvement of the estimate of the onset of maturation is not significant. When applied to growth curves back-calculated from otoliths of female North Sea plaice Pleuronectes platessa, the four-trait and three-trait estimation produced estimates for the onset of maturation very similar to those obtained by direct observation. The correlations between life-history traits match expectations. We discuss the potential of the methodology in studies of the ecology and evolution of life history parameters in wild populations
    Identifying key entry-points for strategic management of smallholder farming systems in sub-Saharan Africa using the dynamic farm-scale simulation model NUANCES-FARMSIM
    Wijk, M.T. van; Tittonell, P.A. ; Rufino, M.C. ; Herrero, M. ; Pacini, C. ; Ridder, N. de; Giller, K.E. - \ 2009
    Agricultural Systems 102 (2009)1-3. - ISSN 0308-521X - p. 89 - 101.
    soil fertility management - term crop response - western kenya - exploring diversity - resource-allocation - use efficiencies - field-scale - productivity - nitrogen - integration
    African smallholder farming systems are complex, dynamic systems with many interacting biophysical subcomponents. In these systems the major inputs and outputs are managed by human agency ¿ the farmers. To analyse potential developmental pathways of smallholder farming systems in sub-Saharan Africa (SSA), we recognised the need for a tool that can capture the effects and consequences of decision-making on the use of resources. Here we describe and apply such a new modelling tool, developed within the NUANCES framework (Nutrient Use in ANimal and Cropping systems: Efficiencies and Scales), called NUANCES-FARMSIM (FARM SIMulator), an integrated crop ¿ livestock model developed to analyse African smallholder farm systems. NUANCES-FARMSIM was used to analyse a representative case study farm in the highlands of Western Kenya, a site for which each of the components of FARMSIM has been thoroughly tested. We present the results of a sensitivity analysis which showed the model to be sufficiently robust to identify key management options that explain most of the variability in farm productivity, and the long-term consequences of these options for the case study farm. The analyses showed clearly that the most important decisions are those related to the interactions between the different components of the farm and therefore justify the need of integrating crop and livestock components within one modelling tool. The allocation of limited resources across the farm, and the way organic matter is recycled or redistributed within the farm determines the long-term production capacity of the system. The results of the sensitivity analyses further showed that for the case study farm in Western Kenya a strong focus on improving the reliability of the subsystem level or process descriptions will only result in minor improvement in simulating productivity at farm level
    Multiple benefits of manure: the key to maintenance of soil fertility and restoration of depleted sandy soils on African smallholder farms
    Zingore, S. ; Delve, R.J. ; Nyamangara, J. ; Giller, K.E. - \ 2008
    Nutrient Cycling in Agroecosystems 80 (2008)3. - ISSN 1385-1314 - p. 267 - 282.
    organic-matter - cattle manure - resource-allocation - crop production - western kenya - acid soils - management - zimbabwe - tropics - variability
    Manure is a key nutrient resource on smallholder farms in the tropics, especially on poorly buffered sandy soils, due to its multiple benefits for soil fertility. Farmers preferentially apply manure to fields closest to homesteads (homefields), which are more fertile than fields further away (outfields). A three-year experiment was established on homefields and outfields on sandy and clayey soils to assess the effects of mineral nitrogen (N) fertilizer application in combination with manure or mineral phosphorus (P) on maize yields and soil chemical properties. Significant maize responses to application of N and manure were observed on all fields except the depleted sandy outfield. Large amounts of manure (17 t ha¿1 year¿1) were required to significantly increase soil organic carbon (SOC), pH, available P, and base saturation, and restore productivity of the depleted sandy outfield. Sole N as ammonium nitrate (100 kg N ha¿1) or in combination with single superphosphate led to acidification of the sandy soils, with a decrease of up to 0.8 pH units after three seasons. In a greenhouse experiment, N and calcium (Ca) were identified as deficient in the sandy homefield, while N, P, Ca, and zinc (Zn) were deficient or low on the sandy outfield. The deficiencies of Ca and Zn were alleviated by the addition of manure. This study highlights the essential role of manure in sustaining and replenishing soil fertility on smallholder farms through its multiple effects, although it should be used in combination with N mineral fertilizers due to its low capacity to supply N.
    Yield gaps, nutrient use efficiencies and response to fertilisers by maize across heterogeneous smallholder farms of western Kenya
    Tittonell, P.A. ; Vanlauwe, B. ; Corbeels, M. ; Giller, K.E. - \ 2008
    Plant and Soil 313 (2008)1-2. - ISSN 0032-079X - p. 19 - 37.
    soil fertility - quantitative-evaluation - resource-allocation - crop productivity - management - variability - gradients - quefts - rice
    The need to promote fertiliser use by African smallholder farmers to counteract the current decline in per capita food production is widely recognised. But soil heterogeneity results in variable responses of crops to fertilisers within single farms. We used existing databases on maize production under farmer (F-M) and researcher management (R-M) to analyse the effect of soil heterogeneity on the different components of nutrient use efficiency by maize growing on smallholder farms in western Kenya: nutrient availability, capture and conversion efficiencies and crop biomass partitioning. Subsequently, we used the simple model QUEFTS to calculate nutrient recovery efficiencies from the R-M plots and to calculate attainable yields with and without fertilisers based on measured soil properties across heterogeneous farms. The yield gap of maize between F-M and R-M varied from 0.5 to 3 t grain ha-1 season-1 across field types and localities. Poor fields under R-M yielded better than F-M, even without fertilisers. Such differences, of up to 1.1 t ha-1 greater yields under R-M conditions are attributable to improved agronomic management and germplasm. The relative response of maize to N-P-K fertilisers tended to decrease with increasing soil quality (soil C and extractable P), from a maximum of 4.4-fold to -0.5- fold relative to the control. Soil heterogeneity affected resource use efficiencies mainly through effects on the efficiency of resource capture. Apparent recovery efficiencies varied between 0 and 70% for N, 0 and 15% for P, and 0 to 52% for K. Resource conversion efficiencies were less variable across fields and localities, with average values of 97 kg DM kg-1 N, 558 kg DM kg-1 P and 111 kg DM kg-1 K taken up. Using measured soil chemical properties QUEFTS over-estimated observed yields under F-M, indicating that variable crop performance within and across farms cannot be ascribed solely to soil nutrient availability. For the R-M plots QUEFTS predicted positive crop responses to application of 30 kg P ha-1 and 30 kg P ha-1 + 90 kg N ha-1 for a wide range of soil qualities, indicating that there is room to improve current crop productivity through fertiliser use. To ensure their efficient use in sub-Saharan Africa mineral fertilisers should be: (1) targeted to specific niches of soil fertility within heterogeneous farms; and (2) go hand-in-hand with the implementation of agronomic measures to improve their capture and utilisation.
    Combining Organic and Mineral Fertilizers for Integrated Soil Fertility Management in Smallholder Farming Systems of Kenya: Explorations Using the Crop-Soil Model FIELD
    Tittonell, P.A. ; Corbeels, M. ; Wijk, M.T. van; Vanlauwe, B. ; Giller, K.E. - \ 2008
    Agronomy Journal 100 (2008)5. - ISSN 0002-1962 - p. 1511 - 1526.
    western kenya - exploring diversity - resource-allocation - use efficiencies - variability - gradients - dynamics - manure - scale - simulation
    Integrated soil fertility management (ISFM) technologies for African smallholders should consider (i) within-farm soil heterogeneity; (ii) long-term dynamics and variability; (iii) manure quality and availability; (iv) access to fertilizers; and (v) competing uses for crop residues. We used the model FIELD (Field-scale resource Interactions, use Efficiencies and Long term soil fertility Development) to explore allocation strategies of manure and fertilizers. Maize response to N fertilizer from 0 to 180 kg N ha¿1 (±30 kg P ha¿1) distinguished poorly responsive fertile (e.g., grain yields of 4.1¿5.3 t ha¿1 without P and of 7.5¿7.5 t ha¿1 with P) from responsive (1.0¿4.3 t ha¿1 and 2.2¿6.6 t ha¿1) and poorly responsive infertile fields (0.2¿1.0 t ha¿1 and 0.5¿3.1 t ha¿1). Soils receiving manure plus fertilizers for 12 yr retained 1.1 to 1.5 t C ha¿1 yr¿1 when 70% of the crop residue was left in the field, and 0.4 to 0.7 t C ha¿1 yr¿1 with 10% left. Degraded fields were not rehabilitated with manures of local quality (e.g., 23¿35% C, 0.5¿1.2% N, 0.1¿0.3% P) applied at realistic rates (3.6 t dm ha¿1 yr¿1) for 12 yr without fertilizers. Mineral fertilizers are necessary to kick-start soil rehabilitation through hysteretic restoration of biomass productivity and C inputs to the soil.
    Grazing, differential size-class dynamics and survival of the Mediterranean sponge Corticium candelabrum
    Caralt, S. de; Uriz, M.J. ; Wijffels, R.H. - \ 2008
    Marine Ecology Progress Series 360 (2008). - ISSN 0171-8630 - p. 97 - 106.
    crambe-crambe poecilosclerida - coral-reef sponges - growth dynamics - population-structure - resource-allocation - mass-mortality - summer 1999 - deep-water - demospongiae - rates
    The growth dynamics and survival of the sponge Corticium candelabrum (Demospongiae: Homosclerophorida) were surveyed in the northwestern Mediterranean for more than 3 yr. Growth and regeneration rates, fission and fusion events and survival were monitored monthly. Moreover, in situ punctual clearance experiments were conducted seasonally searching for possible relationships between food uptake and sponge dynamics. The monthly growth rates (GR) of C. candelabrum were low (0.19 ± 0.02 mean [±SE] for the 3 yr of study), variable and seasonal, with the highest values in summer. The cumulative survival function followed a stepped profile with several consecutive months without mortality separated by shorter mortality events, which mainly occurred in cold months (winter¿spring). However, an event of high mortality (76% of the monitored individuals died) took place in the particularly warm summer 2003. Fission events were frequent after previous damage (e.g. partial predation) and only one fusion event was recorded along the study period. The diet of C. candelabrum was highly heterogeneous. Differences in clearance rates (CR) among picoplankton types with season indicated that the sponge retained with different efficiency the several picoplankton types present in the water. Survival and GRs were significantly different for small, medium and large individuals (size-classes I, II and III), with the small sponges showing the lowest survival (56.6% cumulative mortality for the last 2 yr of study) and the highest GRs (0.18 ± 0.03 mo¿1, mean ± SE). On the whole, the results indicate that C. candelabrum is a slow-growing but dynamic sponge.
    The interplay between shifts in biomass allocation and costs of reproduction in four grassland perennials under simulated successional change
    Jongejans, E. ; Kroon, H. de; Berendse, F. - \ 2006
    Oecologia 147 (2006)2. - ISSN 0029-8549 - p. 369 - 378.
    resource-allocation - nutrient availability - sexual reproduction - population-dynamics - species-diversity - clonal plant - competition - vegetation - heathland - growth
    When perennial herbs face the risk of being outcompeted in the course of succession, they are hypothesized to either increase their biomass allocation to flowers and seeds or to invest more in vegetative growth. We tested these hypotheses in a 3-year garden experiment with four perennials (Hypochaeris radicata, Cirsium dissectum, Succisa pratensis and Centaurea jacea) by growing them in the midst of a tall tussock-forming grass (Molinia caerulea) that may successionally replace them in their natural habitat. In all species except for the short-lived H. radicata, costs of sexual reproduction were significant over the 3 years, since continuous bud removal enhanced total biomass or rosette number. To mimic succession we added nutrients, which resulted in a tripled grass biomass and higher death rates in the shorter-lived species. The simulated succession resulted also in a number of coupled growth responses in the survivors: enhanced plant size as well as elevated seed production. The latter was partly due to larger plant sizes, but mostly due to higher reproductive allocation, which in turn could be partly explained by lower relative somatic costs and by lower root¿shoot ratios in the high-nutrient plots. Our results suggest that perennial plants can increase both their persistence and their colonization ability by simultaneously increasing their vegetative size and reproductive allocation in response to enhanced competition and nutrient influxes. These responses can be very important for the survival of a species in a metapopulation context.
    Flexible life history responses to flower and rosette bud removal in three perennial herbs
    Hartemink, N. ; Jongejans, E. ; Kroon, H. de - \ 2004
    Oikos 105 (2004). - ISSN 0030-1299 - p. 159 - 167.
    resource-allocation - meristem allocation - succisa-pratensis - fruit removal - clonal plant - patterns - growth - reproduction - populations - simulation
    Flexible life history responses to flower and rosette bud removal in three perennial herbs Nienke Hartemink, Eelke Jongejans and Hans de Kroon, In a garden experiment we investigated the response to continuous removal of either flower buds or rosette buds in three perennial grassland species (Hypochaeris radicata, Succisa pratensis and Centaurea jacea), which differ in longevity and flowering type. We distinguished two possible responses: compensation for lost buds by making more buds of the same type, and switching towards development of other life history functions. Both responses were demonstrated in our experiment, but bud removal had significantly different effects in each of the three species. The degree of compensation and the expression of trade-offs between life history functions differed markedly between species and seem related to longevity and developmental constraints. With respect to switching, our results suggest costs of reproduction and a trade-off between life history functions, at least for Hypochaeris and Succisa. For these species weight of new rosettes increased when resource allocation to flowering was inhibited. In Hypochaeris, we see that both compensation for lost flower buds and switching from lost rosette buds increased production of flower buds, underscoring the pivotal role of sexual reproduction in this short-lived species. The most prominent response seen in Centaurea is compensation for lost rosette buds, indicating that this long-lived species with monocarpic rosettes relies on rosette formation. Although Succisa does respond to bud removal, time is an important constraint in this species with long-lived rosettes and preformed flowering stalks. Trade-offs in Succisa seem to operate at a larger time scale, requiring long-lasting experiments to reveal them. We conclude that the response of these species to inflicted damage is likely to be linked to their longevity and developmental constraints.
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