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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    Climate-induced yield variability and yield gaps of maize (Zea mays L.) in the Central Rift Valley of Ethiopia
    Kassie, B.T. ; Ittersum, M.K. van; Hengsdijk, H. ; Asseng, S. ; Wolf, J. ; Rotter, R.P. - \ 2014
    Field Crops Research 160 (2014). - ISSN 0378-4290 - p. 41 - 53.
    sub-saharan africa - use systems-analysis - crop growth-models - ecological intensification - fertilizer application - simulation-model - water-uptake - agriculture - adaptation - ceres
    There is a high demand for quantitative information on impacts of climate on crop yields, yield gaps and their variability in Ethiopia, yet, quantitative studies that include an indication of uncertainties in the estimates are rare. A multi-model crop growth simulation approach using the two crop models, i.e. Decision Support System for Agro-Technology (DSSAT) and WOrld FOod STudies (WOFOST) was applied to characterize climate-induced variability and yield gaps of maize. The models were calibrated and evaluated with experimental data from the Central Rift Valley (CRV) in Ethiopia. Subsequently, a simulation experiment was carried out with an early maturing (Melkassa1) and a late maturing (BH540) cultivar using historical weather data (1984-2009) of three locations in the CRV. Yield gaps were computed as differences among simulated water-limited yield, on-farm trial yields and average actual farmers' yields. The simulation experiment revealed that the potential yield (average across three sites and 1984-2009) is 8.2-9.2 and 6.8-7.1 Mg/ha for the late maturing and early maturing cultivars, respectively; ranges indicate mean differences between the two models. The simulated water-limited yield (averaged across three sites and 1984-2009) is 7.2-7.9 Mg/ha for the late maturing and 6.1-6.7 Mg/ha for the early maturing cultivar. The water-limited yield shows high inter-annual variability (CV 36%) and about 60% of this variability in yield is explained by the variation in growing season rainfall. The gap between average farmers yield and simulated water-limited yield ranges from 4.7 to 6.0 Mg/ha. The average farmers' yields were 2.0-2.3 Mg/ha, which is about 1.1-3.1 Mg/ha lower than on-farm trial yields. In relative terms, average farmers' yields are 28-30% of the water-limited yield and 44-65% of on-farm trial yields. Analysis of yield gaps for different number of years to drive average yields indicates that yield gap estimation on the basis of few years may result in misleading conclusions. Approximately ten years of data are required to be able to estimate yield gaps for the Central Rift Valley in a robust manner. Existing yield gaps indicate that there is scope for significantly increasing maize yield in the CRV and other, similar agro-ecological zones in Africa, through improved crop and climate risk management strategies. As crop models differ in detail of describing the complex, dynamic processes of crop growth, water use and soil water balances, the multi-model approach provides information on the uncertainty in simulating crop-climate interactions. (C) 2014 Elsevier B.V. All rights reserved.
    Going back to the roots: the need to link plant functional biology with vadose zone processes
    Ploeg, M.J. van der; Teuling, A.J. - \ 2013
    Procedia Environmental Sciences 19 (2013). - ISSN 1878-0296 - p. 379 - 383.
    water-uptake - models - drought - genome
    Soil plant atmosphere continuum concepts used in vadose zone hydrology approach plants as physical entities. This approach has proven very valuable in the past decades. The need to upscale such concepts provokes the question if plant functional biology should be considered, as larger scales also imply variation in (micro)climate and soil composition. Habitat manifestation is an expression of its evolutionary history and although the spatial distribution of habitats is largely driven by current climates, a soil's water holding capacity and hence its formation over time may have played a role. Separate mechanisms involved in the soil plant atmosphere continuum are often understood and incorporated in numerical models for predictive purposes, yet interrelationships pose challenges, especially when such relationships cross traditional scientific disciplinary boundaries. In fact, the exact driver for root water uptake is itself subject of scientific debate, as there is no consensus on whether the driver for root water uptake is soil moisture content (e.g. [1]) or soil water potential (e.g. [2]). To evaluate soil water availability in relation to crop yield prognoses and the stability of natural vegetation, integrated concepts are sorely needed, especially in the perspective of climate change [3] and global water scarcity [4]. We present considerations and possible approaches for linking plant functional biology and vadose zone processes.
    Critical soil conditions for oxygen stress to plant roots: substituting the Fedds-function by a process-based model
    Bartholomeus, R.P. ; Witte, J.P.M. ; Bodegom, P.M. van; Dam, J.C. van; Aerts, R. - \ 2008
    Journal of Hydrology 360 (2008)1-4. - ISSN 0022-1694 - p. 147 - 165.
    bodemporiënsysteem - bodemlucht - wateropname (planten) - plant-water relaties - transpiratie - waterverzadiging - modellen - oxidatieve stress - bodem-plant relaties - soil pore system - soil air - water uptake - plant water relations - transpiration - waterlogging - models - oxidative stress - soil plant relationships - use systems-analysis - crop growth-models - physical-properties - water-uptake - diffusion - respiration - aeration - compaction - transport - conductivity
    Effects of insufficient soil aeration on the functioning of plants form an important field of research. A well-known and frequently used utility to express oxygen stress experienced by plants is the Feddes-function. This function reduces root water uptake linearly between two constant pressure heads, representing threshold values for minimum and maximum oxygen deficiency. However, the correctness of this expression has never been evaluated and constant critical values for oxygen stress are likely to be inappropriate. In this paper, we propose a fundamentally different approach to assess oxygen stress: we built a plant physiological and soil physical process-based model to calculate the minimum gas filled porosity of the soil at which oxygen stress occurs.
    Effects of insufficient soil aeration on the functioning of plants form an important field of research. A well-known and frequently used utility to express oxygen stress experienced by plants is the Feddes-function. This function reduces root water uptake linearly between two constant pressure heads, representing threshold values for minimum and maximum oxygen deficiency. However, the correctness of this expression has never been evaluated and constant critical values for oxygen stress are likely to be inappropriate. On theoretical grounds it is expected that oxygen stress depends on various abiotic and biotic factors. In this paper, we propose a fundamentally different approach to assess oxygen stress: we built a plant physiological and soil physical process-based model to calculate the minimum gas filled porosity of the soil (phi gas_min) at which oxygen stress occurs. First, we calculated the minimum oxygen concentration in the gas phase of the soil needed to sustain the roots through (micro-scale) diffusion with just enough oxygen to respire. Subsequently, phi gas_min that corresponds to this minimum oxygen concentration was calculated from diffusion from the atmosphere through the soil (macro-scale). We analyzed the validity of constant critical values to represent oxygen stress in terms Of phi gas_min, based on model simulations in which we distinguished different soil types and in which we varied temperature, organic matter content, soil depth and plant characteristics. Furthermore, in order to compare our model results with the Feddes-function, we linked root oxygen stress to root water uptake (through the sink term variable F, which is the ratio of actual and potential uptake). The simulations showed that phi gas-min is especially sensitive to soil temperature, plant characteristics (root dry weight and maintenance respiration coefficient) and soil depth but hardly to soil organic matter content. Moreover, phi gas-min varied considerably between soil types and was larger in sandy soils than in clayey soils. We demonstrated that F of the Feddes-function indeed decreases approximately linearly, but that actual oxygen stress already starts at drier conditions than according to the Feddes-function. How much drier is depended on the factors indicated above. Thus, the Feddes-function might cause large errors in the prediction of transpiration reduction and growth reduction through oxygen stress. We made our method easily accessible to others by implementing it in SWAP, a user-friendly soil water model that is coupled to plant growth. Since constant values for phi gas_min in plant and hydrological modeling appeared to be inappropriate, an integrated approach, including both physiological and physical processes, should be used instead. Therefore, we advocate using our method in all situations where oxygen stress could occur. (C) 2008 Elsevier B.V. All rights reserved.
    Genotype and planting density effects on rooting traits and yield in cotton (Gossypium hirsutum L.)
    Zhang, L.Z. ; Li, B.G. ; Yan, G.T. ; Werf, W. van der; Spiertz, J.H.J. ; Zhang, S.P. - \ 2006
    Journal of Integrative Plant Biology 48 (2006)11. - ISSN 1672-9072 - p. 1287 - 1293.
    water-uptake - length density - sample preparation - small-diameter - soil-water - growth - maize - systems - shoot - model
    Root density distribution of plants is a major indicator of competition between plants and determines resource capture from the soil. This experiment was conducted in 2005 at Anyang, located in the Yellow River region, Henan Province, China. Three cotton (Gossypium hirsutum L.) cultivars were chosen: hybrid Bt-cultivar CRI46, conventional Bt-cultivars CRI44 and CRI45. Six planting densities were designed, ranging from 1.5 to 12.0 plants/m2Root parameters such as surface area, diameter and length were analyzed by using the DT-SCAN image analysis method. The root length density (RLD), root average diameter and root area index (RAI), root surface area per unit land area, were studied. The results showed that RLD and RAI differed between genotypes; hybrid CRI46 had significantly higher (P <0.05) RLD and RAI values than conventional cultivars, especially under low planting densities, less than 3.0 plants/m2The root area index (RAI) of hybrid CRI46 was 61% higher than of CRI44 and CRI45 at the flowering stage. The RLD and RAI were also significantly different (P = 0.000) between planting densities. The depth distribution of RAI showed that at increasing planting densities RAI was increasingly distributed in the soil layers below 50 cm. The RAI of hybrid CRI46 was for all planting densities, obviously higher than other cultivars during the flowering and boll stages. It was concluded that the hybrid had a strong advantage in root maintenance preventing premature senescence of roots. The root diameter of hybrid CRI46 had a genetically higher root diameter at planting densities lower than 6.0 plants/m2Good associations were found between yield and RAI in different stages. The optimum planting density ranged from 4.50 plants/m2 to 6.75 plants/m2 for conventional cultivars and around 4.0¿5.0 plants/m2 for hybrids.
    Below-ground competition between trees and grasses may overwhelm the facilitative effects of hydraulic lift
    Ludwig, F. ; Prins, H.H.T. ; Berendse, F. ; Kroon, H. de; Dawson, T.E. - \ 2004
    Ecology Letters 7 (2004)8. - ISSN 1461-023X - p. 623 - 631.
    african humid savanna - mojave desert - water-uptake - rooting patterns - east-africa - plants - vegetation - shrubs - transport - nutrients
    Under large East African Acacia trees, which were known to show hydraulic lift, we experimentally tested whether tree roots facilitate grass production or compete with grasses for below-ground resources. Prevention of tree-grass interactions through root trenching led to increased soil water content indicating that trees took up more water from the topsoil than they exuded via hydraulic lift. Biomass was higher in trenched plots compared to controls probably because of reduced competition for water. Stable isotope analyses of plant and source water showed that grasses which competed with trees used a greater proportion of deep water compared with grasses in trenched plots. Grasses therefore used hydraulically lifted water provided by trees, or took up deep soil water directly by growing deeper roots when competition with trees occurred. We conclude that any facilitative effect of hydraulic lift for neighbouring species may easily be overwhelmed by water competition in (semi-) arid regions.
    Hydraulic lift in Acacia tortilis trees on an East African savanna
    Ludwig, F. ; Dawson, T.E. ; Kroon, H. de; Berendse, F. ; Prins, H.H.T. - \ 2003
    Oecologia 134 (2003)3. - ISSN 0029-8549 - p. 293 - 300.
    water-uptake - soil-water - artemisia-tridentata - grass interactions - rooting patterns - humid savanna - plants - woody - kenya - nutrients
    Recent studies suggest that savanna trees in semi-arid areas can increase understorey plant production. We hypothesized that one of the mechanisms that explains the facilitation between trees and grasses in East African savannas is hydraulic lift (HL). HL in large Acacia tortilis trees was studied during the first 3 months of the dry season during a relatively wet year (1998) and a very dry year (2000). In 1998, we found distinct diel fluctuation in soil water potential (psi(S)), with increasing values during the night and decreasing again the following day. These fluctuations in psi(S), are consistent with other observations of HL and in A tortilis were found up to 10 in from the tree. In 2000, during a severe drought, fs measurements indicated that HL was largely absent. The finding that HL occurred in wetter years and not in drier years was supported by data obtained on the 5180 values in soil, rain and groundwater. The 6180 of water extracted from the xylem water of grasses indicated that when they grew near trees they had values similar to those of groundwater. This could be because they either (1) use water from deeper soil layers or (2) use hydraulically lifted water provided by the tree; this was not seen in the same grass species growing outside tree canopies. While our data indicate that HL indeed occurs under Acacia trees, it is also true that psi(S) was consistently lower under trees when compared to outside tree canopies. We believe that this is because tree-grass mixtures take up more water from the upper soil layers than is exuded by the tree each night. This limits the beneficial effect of HL for understorey grasses and suggests that in savannas both facilitation via HL and competition are active processes. The importance of each process may depend upon how wet or dry that particular site or year is.
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