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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    Water-use advantage for lianas over trees in tropical seasonal forests
    Chen, Y.J. ; Cao, K.F. ; Schnitzer, S.A. ; Fan, Z.X. ; Zhang, J.L. ; Bongers, F. - \ 2015
    New Phytologist 205 (2015)1. - ISSN 0028-646X - p. 128 - 136.
    rain-forest - canopy trees - soil-water - sw china - aboveground biomass - secondary forest - eastern amazonia - stomatal control - stable-isotopes - woody-plants
    •Lianas exhibit peak abundance in tropical forests with strong seasonal droughts, the eco-physiological mechanisms associated with lianas coping with water deficits are poorly understood. •We examined soil water partitioning, sap flow, and canopy eco-physiological properties for 99 individuals of 15 liana and 34 co-occurring tree species in three tropical forests that differed in soil water availability. •In the dry season, lianas used a higher proportion of deep soil water in the karst forest (KF; an area with severe seasonal soil water deficit (SSWD)) and in the tropical seasonal forest (TSF, moderate SSWD), permitting them to maintain a comparable leaf water status than trees in the TSF or a better status than trees in the KF. Lianas exhibited strong stomatal control to maximize carbon fixation while minimizing dry season water loss. During the dry period, lianas significantly decreased water consumption in the TSF and the KF. Additionally, lianas had a much higher maximum photosynthetic rates and sap flux density in the wet season and a lower proportional decline in photosynthesis in the dry season compared with those of trees. •Our results indicated that access to deep soil water and strong physiological adjustments in the dry season together with active wet-season photosynthesis may explain the high abundance of lianas in seasonally dry forests.
    Phenological development of East African highland banana involves trade-offs between physiological age and chronological age
    Taulya, G. ; Asten, P.J.A. van; Leffelaar, P.A. ; Giller, K.E. - \ 2014
    European Journal of Agronomy 60 (2014). - ISSN 1161-0301 - p. 41 - 53.
    relative growth-rate - musa-spp. - plant-growth - life-history - soil-water - leaf-area - photosynthesis - acclimation - temperature - yield
    The phenology of East African highland banana (Musa acuminata AAA-EA, hereafter referred to as ‘highland banana’) is poorly understood. We tested three hypotheses: (1) the physiological age at flowering is independent of site effects, (2) there is no difference in threshold size at flowering between sites with different growth potential, and (3) morphological and physiological components of highland banana relative growth rate (RGR) contribute equally to mitigate growth reduction in response to limiting supply of water, K or N. The physiological age of highland banana plants from field trials at Kawanda (central Uganda) and Ntungamo (south-western Uganda) was computed from daily temperature records. Growth analysis was conducted using RGR, net assimilation rate (NAR), specific leaf area (SLA) and leaf mass ratio (LMR) estimated from allometry. Growth response coefficients were used for quantifying the relative contribution of NAR, SLA and LMR to RGR. Physiological age at flowering was delayed by 739 °C d at Kawanda compared with that at Ntungamo whose chronological age at flowering was in turn 51 d older. At both sites a threshold total dry mass of 1.5 kg per plant was required for flowering. Faster absolute growth rate and NAR fostered by wet conditions, K input and cooler temperatures enabled plants at Ntungamo to attain the threshold total dry mass sooner than those at Kawanda, hence the phenotypic plasticity in age at flowering. Net assimilation rate contributed at least 90% to RGR increase due to wet conditions at both sites. The contribution of NAR to RGR increase in response to K at Kawanda reduced to 38% while that for SLA increased to 49%. Net assimilation rate contributes more to highland banana RGR modulation than SLA except when warmer conditions reduce NAR. Differences in crop growth rate cause phenotypic plasticity in highland banana rate of phenological development.
    East African highland bananas (Musa spp. AAA-EA) 'worry' more about potassium deficiency than drought stress
    Taulya, G. - \ 2013
    Field Crops Research 151 (2013). - ISSN 0378-4290 - p. 45 - 55.
    foliar nutrient status - biomass allocation - osmotic adjustment - plant-growth - root ratio - soil-water - nitrogen - shoot - fertilizer - weevil
    Drought stress, potassium (K) and nitrogen (N) deficiencies are major constraints to rain-fed East African highland banana (EAHB) production in Uganda. It was hypothesised that the reduction in fresh bunch mass and increase in dry matter (DM) allocation to corms with drought stress, K and N deficiency is additive. Individual plant measurements at harvest from two field trials in central and south western Uganda were analyzed to evaluate effects of cumulative rainfall (CRF) received 365 days from sucker emergence, mineral K and N inputs on EAHB bunch yields. Dry matter content in aerial shoot (leaves and pseudostems) relative to that in the subterranean corm was also analyzed to evaluate DM allocation plasticity due to drought stress, K and N deficiency. This was verified with allometric analysis using pre-harvest stage plants from farms of known K and N nutritional status and plants from a screen house drought stress pot trial in Uganda. Dry matter production and yields were mainly driven by K interacting with CRF. Within 12 months, K input (250-600 kg K ha(-1) yr(-1)) increased bunch yield from 8 to 15 Mg ha(-1) yr(-1) irrespective of whether dry (CRF <1100 mm) or wet (CRF >= 1100 mm) conditions prevailed, possibly due to K-mediated osmotic adjustment under dry conditions. Without K input, wet conditions increased bunch yield from 6 to 8 Mg ha(-1) yr(-1) while dry conditions decreased it from 6 to 4 Mg ha(-1) yr(-1) within 12 months. Total DM and its distribution between the biomass structures followed similar trends. Nitrogen input (150-400 kg N ha(-1) yr(-1)) neither affected bunch yield nor DM allocation at harvest stage. At pre-harvest stage, reduction in DM allocation to the corm per unit increase in total DM was 14-22% significantly lower with N and/or K deficiency compared with that under sufficient K and N. Drought stress per se had no effect on DM allocation but enhanced DM allocation shifts due to K deficiency. Drought-stressed EAHB thus increase DM allocation to subterranean structures only if K-deficient, unlike responses reported for other plant species. Potassium nutrition is perhaps a more viable entry point for mitigation of drought stress in EAHB cropping systems than irrigation but this requires further agronomic and economic evaluation. It may be important to account for carbon allocated to osmotic adjustment for realistic simulation of water- and K-limited growth in EAHB. (c) 2013 Elsevier B.V. All rights reserved.
    Evaluation of MODIS gross primary productivity for Africa using eddy covariance data
    Sjostrom, M. ; Zhao, M. ; Archibald, S. ; Veenendaal, E.M. - \ 2013
    Remote Sensing of Environment 131 (2013). - ISSN 0034-4257 - p. 275 - 286.
    net primary production - deciduous broadleaf forest - primary production gpp - light use efficiency - ecosystem exchange - soil-water - spatial variability - terrestrial gross - savanna ecosystem - carbon-dioxide
    MOD17A2 provides operational gross primary production (GPP) data globally at 1 km spatial resolution and 8-day temporal resolution. MOD17A2 estimates GPP according to the light use efficiency (LUE) concept assuming a fixed maximum rate of carbon assimilation per unit photosynthetically active radiation absorbed by the vegetation (emax). Minimum temperature and vapor pressure deficit derived from meteorological data down-regulate emax and constrain carbon assimilation. This data is useful for regional to global studies of the terrestrial carbon budget, climate change and natural resources. In this study we evaluated the MOD17A2 product and its driver data by using in situ measurements of meteorology and eddy covariance GPP for 12 African sites. MOD17A2 agreed well with eddy covariance GPP for wet sites. Overall, seasonality was well captured but MOD17A2 GPP was underestimated for the dry sites located in the Sahel region. Replacing the meteorological driver data derived from coarse resolution reanalysis data with tower measurements reduced MOD17A2 GPP uncertainties, however, the underestimations at the dry sites persisted. Inferred emax calculated from tower data was higher than the emax prescribed in MOD17A2. This, in addition to uncertainties in fraction of absorbed photosynthetically active radiation (FAPAR) explains some of the underestimations. The results suggest that improved quality of driver data, but primarily a readjustment of the parameters in the biome parameter look-up table (BPLUT) may be needed to better estimate GPP for African ecosystems in MOD17A2.
    Pressure Heads and Simulated Water Uptake Patterns for a Severely Stressed Bean Crop
    Durigon, A. ; Santos, M.A. dos; Lier, Q.D. van; Metselaar, K. - \ 2012
    Vadose Zone Journal 11 (2012)3. - ISSN 1539-1663
    root hydraulic conductivity - flux potential approach - polymer tensiometers - soil-water - wilting point - transpiration - evaporation - model - architecture
    In modeling, actual crop transpiration as a function of soil hydraulic conditions is usually estimated from a water content or pressure head dependent reduction function. We compared the performance of the empirical pressure head based reduction function of Feddes (FRF) and a more physically based reduction function using matric flux potential as the main parameter (DRF), both available in the SWAP ecohydrological model. Model performance was evaluated by comparison of SWAP predictions and observed water contents and pressure head values in a field experiment with a common bean (Phaseolus vulgaris L.) crop. For >50 d, no rain occurred and the soil reached very dry conditions with pressure heads in the range -100 to -150 m. The SWAP-DRF-predicted pressure head and water content values were less sensitive to root length density distribution than those predicted by SWAP-FRF. Varying wilting pressure head did not improve predictive performance. Root water uptake distribution with time and depth simulated by SWAP showed very different patterns depending on the reduction function used. Root water uptake estimated by SWAP-FRF showed smooth transitions with time and between layers, whereas SWAP-DRF, highly sensitive to hydraulic conditions, generally predicted uptake to be concentrated at a few depths. The order of magnitude of the pressure head difference between root xylem and root surface based on SWAP-DRF-predicted uptake rates, root length density, and reported values of root conductance was the same as the order of magnitude of the limiting root water pressure head, implying the necessity to include root hydraulic resistance in the DRF.
    Genetic dissection of drought tolerance and recovery potential by quantitative trait locus mapping of a diploid potato population
    Anithakumari, A.M. ; Nataraja, K.N. ; Visser, R.G.F. ; Linden, C.G. van der - \ 2012
    Molecular Breeding 30 (2012)3. - ISSN 1380-3743 - p. 1413 - 1429.
    carbon-isotope discrimination - water-use efficiency - chlorophyll fluorescence - solanum-tuberosum - transpiration efficiency - soil-water - arabidopsis-thaliana - arid conditions - winter-wheat - leaf growth
    Potato is the third most important staple food crop in terms of consumption, yet it is relatively susceptible to yield loss because of drought. As a first step towards improving drought tolerance in this crop, we set out to identify the genetic basis for drought tolerance in a diploid potato mapping population. Experiments were carried out under greenhouse conditions in two successive years by recording four physiological, seven growth and three yield parameters under stress and recovery treatments. Genotypes showed significant variation for drought and recovery responses. The traits measured had low to moderately high heritabilities (ranging from 22 to 74 %). A total of 47 quantitative trait loci (QTL) were identified, of which 28 were drought-specific, 17 under recovery treatment and two under well-watered conditions. The majority of these growth and yield QTL co-localized with a QTL for maturity on chromosome 5. Four QTL for d13C, three for chlorophyll content and one for chlorophyll fluorescence (Fv/Fm) were found to co-localize with yield and other growth trait QTL identified on other chromosomes. Several multi-year and multi-treatment QTL were detected and QTL 9 environment interaction was found for d13C. To our knowledge, this is the first comprehensive QTL study on water deficit and recovery potential in potato.
    Tillage and crop residue effects on rainfed wheat and maize production in Northern China
    Wang Xiaobin, ; Wu Huijin, ; Dai Kuai, ; Zhang Dingchen, ; Feng Donghui, ; Zhao Quansheng, ; Wu Xueping, ; Jin Ke, ; Cai Diangxiong, ; Oenema, O. ; Hoogmoed, W.B. - \ 2012
    Field Crops Research 132 (2012). - ISSN 0378-4290 - p. 106 - 116.
    conservation tillage - management-practices - thermal-properties - soil-water - no-tillage - yield - availability - agriculture - adoption - stubble
    Dryland farming in the dry semi-humid regions of northern China is dominated by mono-cropping systems with mainly maize (Zea mays L.) or wheat (Triticum aestivum), constrained by low and variable rainfall, and by improper management practices. Addressing these problems, field studies on tillage and residue management for winter wheat and spring maize were conducted at 4 sites in Linfen, Tunliu and Shouyang (Shanxi province) and Luoyang (Henan province). These studies (a.o.) explored the impacts of different tillage and residue application methods on soil physical conditions, water storage, water use, water use efficiency (WUE) and crop yields of wheat and maize. An analysis of the results of these studies is presented. Conservation tillage, comprising no-till as well as reduced tillage practices (subsoiling, deep ploughing) showed benefits which were more prominent in combination with residue application. Benefits compared to conventional tillage were found in the form of improved soil physical conditions, such as higher topsoil bulk densities but lower subsoil bulk densities. This resulted in a better water storage during the summer fallow or rainy season in winter wheat fields, and a better water conservation and soil protection in spring maize fields. Compared to conventional methods, reduced tillage gave yields around 13–16% higher in spring maize and round 9–37% higher in winter wheat. Yields under no-till were very close to those from conventional methods. Surface application of crop residue for maize was found to increase the risk for delayed seedling emergence, because of low temperatures, leading to a recommendation for incorporation of residue in combination with reduced tillage. For winter wheat, subsoiling in combination with straw mulching after harvest in summer every other two or three year, and no-till seeding is a promising practice for sandier soils and low rainfall conditions. For heavier clay loam soils, deep ploughing with straw mulching after wheat harvest in summer every other two or three year, and no-till seeding practice is recommended. For spring maize, deep ploughing with straw and fertilizers incorporation after harvest in fall, and no-till seeding practices are recommended. Subsoiling or no-till with residue mulching after harvest in fall, and no-till seeding practices in spring are also promising practices, the latter only in situations where low spring temperatures are not a problem. Continuous no-till is not recommended
    The spatial pattern of grasses in relation to tree effects in an arid savannah community: Inferring the relative importance of canopy and root effect
    Xu, C. ; Liu, M.S. ; Zhang, M. ; Chen, B. ; Huang, Z. ; Uriankhai, T. ; Sheng, S. - \ 2011
    Journal of Arid Environments 75 (2011)10. - ISSN 0140-1963 - p. 953 - 959.
    below-ground competition - positive interactions - plant-communities - soil-water - facilitation - distributions - ecosystems - woody - productivity - understorey
    Both aboveground and belowground processes play important roles in tree-grass interactions in savannas. Little consideration has been given to within-site heterogeneity in the strengths of co-occurring canopy and root effects of trees on grasses in savanna communities. Here, we attempted to correlate the spatial pattern of grass morphological traits with the strengths of canopy and root effects. The results from a spatial analysis suggested that the grass traits had lower variability within the operating domain of the root effect than within that of the canopy effect in sub-canopy areas; in contrast, the operating domain of the root effect presented higher variability of grass traits than that of the canopy effect in inter-canopy areas. Combined with root investigations on vertical distribution patterns, these results suggested that the root effect appeared to outweigh the canopy effect in the sub-canopy areas, where apparent vertical root separation between trees and grasses was shown; while the canopy effect could outweigh the root effect in the inter-canopy areas, where root separation was not observed. This study could provide correlative information on the relative importance of canopy and root effects, and has some useful implications on within-site heterogeneity in terms of aboveground and belowground components in savannas.
    Scales in single root water uptake models: a review, analysis and synthesis
    Metselaar, K. ; Lier, Q.D. van - \ 2011
    European Journal of Soil Science 62 (2011)5. - ISSN 1351-0754 - p. 657 - 665.
    zea-mays l - soil-water - plant-roots - porous-media - hydraulic conductivity - computed-tomography - system architecture - nutrient-uptake - sample-size - volume
    Scales in transport of water to roots are compared with the length and volume scales by using the concepts associated with the representative elementary volume (REV). The possibility of a mismatch between model scale and system scale when using a Darcy-Buckingham-based model to describe soil water transport to a single root is evaluated. In the absence of a mismatch, the replication requirements for evaluating the Darcy-Buckingham-based model near a single root are discussed by using a synthesis of the elementary scales involved, including those for soil, plant and roots, and of the measurement device. By using REV scales from lattice-Boltzmann simulations, the effective half-root mean distance and the available measurement techniques, the evaluation of Darcy-based single root uptake models is possible in roughly 50% of the combinations of soil- and root-system properties. On the basis of an assessment of the scale characterizing natural soil variability, the number of replicates required to assess the average root water uptake profile near a single root is large, and either requires miniaturization of the measurement methods for the hydraulic transport characteristics, or very homogeneous (artificial) growing media with little variability. Variability of water uptake per unit root length will increase the number of samples required.
    Drought is a major yield loss factor for rainfed East African highland banana
    Asten, P. van; Asten-Fermont, A.M. van; Taulya, G. - \ 2011
    Agricultural Water Management 98 (2011)4. - ISSN 0378-3774 - p. 541 - 552.
    a pan evaporation - boundary line - musa-spp. - water-use - soil-water - growth - irrigation - uganda - crop - management
    Although drought stress has been identified among the production constraints of East African highland bananas (Musa spp., AAA-EA genome), no quantitative data were available to support this assumption. This study uses data from three on-station fertilizer trials (5–6 cycles) in Central and Southwest Uganda to quantify the effect of drought stress on banana production and explore possible interactions with nutrient availability. Production data were collected at individual plant basis from 1996 to 2002 in one trial and from 2004 to 2009 in two trials. Cumulative rainfall in the 12 months before harvest (CRF12) was computed per plant from daily rainfall measurements. Average bunch weight ranged from 8.0 to 21.9 kg between trials and cycles and was 8–28% less in dry (CRF12 = 905 mm) than in normal (905
    Nitrogen Leaching in Intensive Cropping Systems in Tam Duong District, Red River Delta of Vietnam
    Trinh, M.V. ; Keulen, H. van; Roetter, R.P. - \ 2010
    Water Air and Soil Pollution 210 (2010)1-4. - ISSN 0049-6979 - p. 15 - 31.
    flooded rice fields - north china plain - water-movement - balance model - soil-water - nitrate - simulation - dynamics - groundwater - management
    The environmental and economic consequences of nitrogen (N) lost in rice-based systems in Vietnam is important but has not been extensively studied. The objective of this study was to quantify the amount of N lost in major cropping systems in the Red River Delta. An experiment was conducted in the Red River Delta of Vietnam, on five different crops including rose, daisy, cabbage, chili, and a rice–rice–maize rotation during 2004 and 2005. Core soil samples were taken periodically in 20-cm increments to a depth of 1 m and analyzed for nitrate–nitrogen and ammonium–nitrogen. The results indicate appreciable leaching losses on N in high-rainfall and irrigation conditions, especially when fertilizer application was not well synchronized with crop N demand. Highest annual leaching losses of N were recorded in flowers with 185–190 mm of percolation and 173–193 kg N ha-1, followed by vegetable (cabbage and chili) with 120–122 mm of percolation and 112–115 kg N ha-1, while it was lowest in rice with about 50 kg N ha-1. We developed a simple N transport model that combined water and N movement through the soil profile. In most cases, the model accurately predicted the seasonal dynamics of N as well as N flow between soil layers and the amounts of N lost from the soil profile. The simulated results of N leaching with soil “puddling” conditions illustrate the advantage of an impermeable or hardpan layer in increasing water and nutrient use efficiencies in these soils. These model results also showed that it is possible to accurately estimate N losses with only a few parameters and helped us identify the risks of N leaching.
    Root water extraction under combined water and osmotic stress
    Jong van Lier, Q. de; Dam, J.C. van; Metselaar, K. - \ 2009
    Soil Science Society of America Journal 73 (2009). - ISSN 0361-5995 - p. 862 - 875.
    irrigating forage crops - soil-water - nutrient-uptake - saline waters - plant - simulation - growth - transpiration - transport - flux
    Using a numerical implicit model for root water extraction by a single root in a symmetric radial flow problem, based on the Richards equation and the combined convection-dispersion equation, we investigated some aspects of the response of root water uptake to combined water and osmotic stress. The model implicitly incorporates the effect of simultaneous pressure head and osmotic head on root water uptake, and does not require additional assumptions (additive or multiplicative) to derive the combined effect of water and salt stress. Simulation results showed that relative transpiration equals relative matric flux potential, which is defined as the matric flux potential calculated with an osmotic pressure head-dependent lower bound of integration, divided by the matric flux potential at the onset of limiting hydraulic conditions. In the falling rate phase, the osmotic head near the root surface was shown to increase in time due to decreasing root water extraction rates, causing a more gradual decline of relative transpiration than with water stress alone. Results furthermore show that osmotic stress effects on uptake depend on pressure head or water content, allowing a refinement of the approach in which fixed reduction factors based on the electrical conductivity of the saturated soil solution extract are used. One of the consequences is that osmotic stress is predicted to occur in situations not predicted by the saturation extract analysis approach. It is also shown that this way of combining salinity and water as stressors yields results that are different from a purely multiplicative approach. An analytical steady state solution is presented to calculate the solute content at the root surface, and compared with the outputs of the numerical model. Using the analytical solution, a method has been developed to estimate relative transpiration as a function of system parameters, which are often already used in vadose zone models: potential transpiration rate, root length density, minimum root surface pressure head, and soil -h and K-h functions
    Macroscopic root water uptake distribution using a matric flux potential approach
    Jong van Lier, Q. de; Dam, J.C. van; Metselaar, K. ; Jong, R. de; Duijnisveld, W.H.M. - \ 2008
    Vadose Zone Journal 7 (2008)3. - ISSN 1539-1663 - p. 1065 - 1078.
    bodemwater - bodem-plant relaties - wateropname (planten) - modellen - soil water - soil plant relationships - water uptake - models - soil-water - extraction patterns - numerical-simulation - stomatal conductance - gas-exchange - sap flow - stress - photosynthesis - transpiration - recovery
    Hydrological models featuring root water uptake usually do not include compensation mechanisms such that reductions in uptake from dry layers are compensated by an increase in uptake from wetter layers. We developed a physically based root water uptake model with an implicit compensation mechanism.
    Hydrological models featuring root water uptake usually do not include compensation mechanisms such that reductions in uptake from dry layers are compensated by an increase in uptake from wetter layers. We developed a physically based root water uptake model with an implicit compensation mechanism. Based on an expression for the matric flux potential (M) as a function of the distance to the root, and assuming a depth-independent value of M at the root surface, uptake per layer is shown to be a function of layer bulk M, root surface M, and a weighting factor that depends on root length density and root radius. Actual transpiration can be calculated from the sum of layer uptake rates. The proposed reduction function (PRF) was built into the SWAP model, and predictions were compared to those made with the Feddes reduction function (FRF). Simulation results were tested against data from Canada (continuous spring wheat [(Triticum aestivum L.]) and Germany (spring wheat, winter barley [Hordeum vulgare L.], sugarbeet [Beta vulgaris L.], winter wheat rotation). For the Canadian data, the root mean square error of prediction (RMSEP) for water content in the upper soil layers was very similar for FRF and PRF; for the deeper layers, RMSEP was smaller for PRF. For the German data, RMSEP was lower for PRF in the upper layers and was similar for both models in the deeper layers. In conclusion, but dependent on the properties of the data sets available for testing,the incorporation of the new reduction function into SWAP was successful, providing new capabilities for simulating compensated root water uptake without increasing the number of input parameters or degrading model performance.
    Sensitivity of a crop growth simulation model to variation in LAI and canopy nitrogen used for run-time calibration
    Jongschaap, R.E.E. - \ 2007
    Ecological Modelling 200 (2007)1-2. - ISSN 0304-3800 - p. 89 - 98.
    leaf-area index - hyperspectral vegetation indexes - chlorophyll density - light reflectance - soil-water - maize - field - balances - equation - system
    Run-time calibration, i.e. adjusting simulation results for field observations of model driving variables during run-time, may allow correcting for deviations between complex mechanistic simulation model results and actual field conditions. Leaf area index (LAI) and canopy nitrogen contents (LeafNWt) are the most important driving variables for these models, as they govern light interception and photosynthetic production capacity of the crop. Remote sensing may provide (spatial) data from which such information can be estimated. How, when and at what frequency such additional information is integrated in the simulation process may have various effects on the simulations. The objective of this study was to quantify the effects of different run-time calibration scenarios for final grain yield (FGY) simulations in order to optimize remote sensing image (RS) acquisition. The PlantSys model was calibrated on LAI and LeafNWt for maize in France and used to simulate maize crop growth in the Argentina and the USA, for which non-destructive estimates of LAI and leaf chlorophyll contents were acquired by optical measurement techniques. Leaf chlorophyll data were used to estimate LeafNWt. Due to its structure, the PlantSys model was more susceptible to run-time calibration with LeafNWt than with LAI. Run-time calibration with LAI showed the largest effect on FGY before and around flowering, and could mainly be related to maintenance respiration costs. Run-time calibration with LeafNWt showed the largest effect on FGY at and after flowering and could mainly be related to the change in effective radiation interception due to change in leaf life. The accuracy of LAI estimates showed a major effect on FGY for underestimations but was small in absolute sense. The accuracy of LeafNWt estimates had significant impact at all crop development stages, but was the strongest after flowering where crop growth and nitrogen uptake are less able to recuperate from changes in LeafNWt. In absolute sense, the effect on FGY was as strong as the accuracy of the LeafNWt estimates when applied in the early reproductive stages. Based on these results it was concluded that remotely sensed in-field variability of LAI and LeafNWt is valuable information that can be used to spatially differentiate model simulations. Run-time calibration at sub-field level may lead to more accurate simulation results for whole fields.
    Water use of tree lines: importance of leaf area and micrometeorology in sub-humid Kenya
    Radersma, S. ; Ong, C.K. ; Coe, R. - \ 2006
    Agroforestry Systems 66 (2006)3. - ISSN 0167-4366 - p. 179 - 189.
    eucalyptus-grandis trees - pinus-radiata - soil-water - growth - transpiration - model - stand - evaporation - simulation - efficiency
    In this research the relative importance of leaf area and microclimatic factors in determining water use of tree lines was examined in sub-humid Western Kenya. Measurements of tree water-use by a heat-balance technique, leaf area, bulk air saturation deficit, daily radiation, and soil water content were done in an experiment with tree lines within crop fields. The tree species were Eucalyptus grandis W. Hill ex Maiden, Grevillea robusta A. Cunn. and Cedrella serrata Royle, grown to produce poles on a phosphorus-fixing Oxisol/Ferralsol with (+P) or without (-P) phosphorus application. Doubling the leaf area of Cedrella and Grevillea doubled water use in a leaf area (LA) range of 1-11 m(2) per tree. The response of Eucalyptus water use (W) to increases in leaf area was slightly less marked, with W = LA(n), n <1. Transpiration rate per unit leaf area (Tr) was the other important determinant of water use, being affected by both tree species and phosphorus fertilization. A doubling of the saturation deficit (SD) halved the water use of all trees except for Cedrella +P, in which water use increased. A direct effect of soil water content on water use was only found in Grevillea -P, with a small increase (60%) as available water increased from 1.4 to 8.9% above wilting point (32%). This low direct response to soil water content is probably due to the extensive tree-root systems and the deep clayey soils supplying sufficient water to meet the evaporative demand. Indirect responses to soil water content via decreases in leaf area occurred in the dry season. The results showed that water use of tree lines was more determined by leaf area and transpiration rate per unit leaf area than by micro meteorological factors. The linear response of tree water use to leaf area, over a wide range leaf areas, is a specific characteristic of tree line configurations and distinguished them from forest stands. In tree lines light interception and canopy conductance increase with leaf area much more than a similar leaf area increase would have caused in a closed forest canopy.
    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.
    Root characteristics of selected field crops: data from the Wageningen Rhizolab (1990-2002)
    Smit, A.L. ; Groenwold, J. - \ 2005
    Plant and Soil 272 (2005)1-2. - ISSN 0032-079X - p. 365 - 384.
    nitrogen catch crops - shoot-atmosphere interactions - nematodes globodera-pallida - brussels-sprouts - cyst nematodes - succeeding crop - winter-wheat - soil-water - growth - dynamics
    Since being built in 1990, the rhizotron facility in Wageningen, the Wageningen Rhizolab, has been used for experiments on crops (e.g. Alfalfa, Brussels sprouts, common velvet grass, field bean, fodder radish, leeks, lupins, maize, potato, beetroot, ryegrass, spinach, spring wheat, winter rye and winter wheat). In the experiments, horizontal glass minirhizotron tubes combined with auger sampling were used to assess rooting characteristics. For this paper we took the root data from these experiments and looked for a general relationship between thermal time/time after planting and rooting depth, the velocity of the root front and root proliferation. For certain depths (fixed by the depth at which the horizontal minirhizotrons were installed) a simple linear regression was established between the average root number per cm2 minirhizotron surface area and thermal time after planting. The compartments selected for each crop were those in which there had been a control treatment and/or in which conditions for rooting were considered to be optimal. We performed regression analyses per compartment and per depth, but only for the period after planting in which a linear increase of root numbers vs. thermal time was observed. After averaging the results, the regression procedure yielded two parameters of rooting for each crop: (a) the actual or thermal time at which the first root appeared at a certain depth and (b) the root proliferation rate after the first root had appeared. In this way, inherent crop differences in rooting behaviour (rooting depth and root proliferation) became apparent. For each crop, the velocity of the root front after planting could be established (calculated in cm(°C day)-1). This parameter differed greatly between crops. Some crops (such as leeks and common velvet grass) explored the soil profile slowly: the root front moved at a velocity of only 0.07cm(°C day)-1. Among the crops whose roots grew down much faster (0.18-0.26cm (°C day)-1) were cereals and fodder radish. For a day with an average temperature of 15°C these rates would have corresponded with the root front travelling approximately 1-4cm per day. In the crops studied the root front velocity did not correlate with the root proliferation rate
    History and prospect of catchment biogeochemistry: a european perspective based on acid rain
    Breemen, N. van; Wright, R.F. - \ 2004
    Ecology 85 (2004)9. - ISSN 0012-9658 - p. 2363 - 2368.
    verzuring - oppervlaktewater - zure regen - luchtverontreiniging - biogeochemie - monitoring - stroomgebieden - aquatisch milieu - acidification - surface water - acid rain - air pollution - biogeochemistry - monitoring - watersheds - aquatic environment - experimental lakes area - experimental acidification - ecosystem experiments - nitrogen saturation - ammonium-sulfate - soil-water - forest - deposition - project - budgets
    Hydrochemical monitoring of catchments provided a philosophical framework as well as hard data to understand and quantify the linked biological and abiotic processes that explain how atmospheric deposition of S and N changed soils and waters in nonagricultural areas across Europe. Initially, as a tool to collect relevant data in a representative and systematic way, hydrochemical monitoring provided evidence for widespread surface water acidification related to atmospheric pollution and long-range air transport. Recognizing the strong effect biota can have on their chemical environment, in the context of catchment biogeochemistry, these data provided new insights into individual processes of soil and water acidification and helped to quantify the relative importance of natural and anthropogenic sources of H+. Furthermore, combined with large-scale ecosystem manipulation and modeling, catchment biogeochemistry offered an effective tool to investigate risks of acidification and of nitrogen saturation of soils and waters
    Evapotranspiration components determined by stable isotope, sap flow and eddy covariance techniques
    Williams, D.G. ; Cable, W. ; Hultine, K. ; Hoedjes, J.C.B. ; Yepez, E.A. ; Simonneaux, V. ; Er-Raki, S. ; Boulet, G. ; Debruin, H.A.R. ; Chehbouni, A. ; Hartogensis, O.K. ; Timouk, F. - \ 2004
    Agricultural and Forest Meteorology 125 (2004)3-4. - ISSN 0168-1923 - p. 241 - 258.
    water-vapor - soil-water - flux measurements - carbon-dioxide - forest canopy - gas-exchange - leaf water - heat - surface - desert
    Understanding and modeling water exchange in and and semiarid ecosystems is complicated by the very heterogeneous distribution of vegetation and moisture inputs, and the difficulty of measuring and validating component fluxes at a common scale. We combined eddy covariance (EC), sap flow, and stable isotope techniques to investigate the responses of transpiration and soil evaporation to an irrigation event in an olive (Olea europaea L.) orchard in Marrakech, Morocco. The primary goal was to evaluate the usefulness of stable isotope measurements of water vapor in the turbulent boundary layer for partitioning evapotranspiration under Such dynamic conditions. The concentration and deuterium isotope composition (delta(2)H) of water vapor was collected from different heights within the ecosystem boundary layer of the olive canopy before and over several days following a 100mm surface irrigation. 'Keeling plots' (isotope turbulent mixing relationships) were generated from these data to estimate the fractions of evaporation and transpiration contributing to the total evapotranspiration (ET) flux. Transpiration accounted for 100% of total ET prior to irrigation, but only 69-36% of ET during peak midday fluxes over the 5-day period following irrigation. The rate of soil evaporation and plant transpiration at the stand level was calculated from eddy covariance measurements and the evaporation and transpiration fractions from isotope measurements. Soil evaporation rate was positively correlated with daily atmospheric vapor pressure deficit (D), but transpiration was not. Component fluxes estimated from the isotope technique were then compared to those obtained from scaled sap flow measurements. Sap flow in multiple-stemmed trees increased following the irrigation, but large single-stemmed trees did not. We matched the source area for eddy covariance estimates of total ET fluxes with scaled sap flow estimates developed for the different tree types. Soil evaporation was determined from the difference between total ET and the scaled sap flow. Ecosystem-level transpiration and soil evaporation estimated by the isotope approach were within 4 and 15% of those estimated by scaled sap flow, respectively, for periods of peak fluxes at midday. Our data illustrate the utility of the isotope 'Keeling plot' approach for partitioning ET at the ecosystem scale on short time steps and the importance of accurate spatial representation of scaled sap flow for comparison with eddy covariance measurements of ET. (C) 2004 Elsevier B.V. All rights reserved.
    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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