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The leaf photosynthesis models developed by Farquhar et al. (1980, https://doi.org/10.1007/BF00386231) (FvCB) and Goudriaan et al. (1985, https://doi.org/10.1007/978-1-4899-3665-3_10) (G85) are both used in Earth system and weather models to quantify ecosystem carbon assimilation. Despite their common role, a systematic comparison between these two photosynthesis models is currently lacking in scientific literature. In this technical report we compared the two models in a systematic way. Hereto we performed a comparative analysis of the model structures as well as the modeled responses of photosynthesis to light and CO2 at leaf level. To facilitate future model comparison, we also constructed a lookup table that presents FvCB model parameters fitted to CO2-response curves from G85 in a wide natural range in photosynthetic capacity at standardized temperature. The structure of the FvCB model differs fundamentally from the G85 model as the FvCB model considers rate-limiting processes due to Rubisco capacity, electron transport and triose phosphate utilization in parallel, whereas the G85 model considers Rubisco activity and triose phosphate utilization limitation to act in series scaled with quantum use efficiency. The models also differ fundamentally in terms of the parametrization of dark respiration. Still, both models calculate near-similar responses of photosynthesis to changes in light and CO2 across a wide range in photosynthetic capacity with only two free parameters each. Our work thereby highlights functional similarities between these model approaches despite fundamental differences in model structure. Hence, standardized parameter sets that yield similar photosynthesis responses to light and CO2 may facilitate intercomparison of Earth system and weather models.

The leaf photosynthesis models developed by Farquhar et al. (1980) (FvCB) and Goudriaan et al. (1985) (G85) are both used in Earth system and weather models to quantify ecosystem carbon assimilation. Despite their common role, a systematic comparison between these two photosynthesis models is currently lacking in scientific literature. In this technical report we compared the two models in a systematic way. Hereto we performed a comparative analysis of the model structures as well as the modeled responses of photosynthesis to light and CO2 at leaf level. To facilitate future model comparison, we also constructed a lookup table that presents FvCB model parameters fitted to CO2-response curves from G85 in a wide natural range in photosynthetic capacity at standardized temperature. The structure of the FvCB model differs fundamentally from the G85 model as the FvCB model considers rate-limiting processes due to Rubisco capacity, electron transport and triose phosphate utilization in parallel, whereas the G85 model considers Rubisco activity and triose phosphate utilization limitation to act in series scaled with quantum use efficiency. The models also differ fundamentally in terms of the parametrization of dark respiration. Still, both models calculate near-similar responses of photosynthesis to changes in light and CO2 across a wide range in photosynthetic capacity with only two free parameters each. Our work thereby highlights functional similarities between these model approaches despite fundamental differences in model structure. Hence, standardized parameter sets that yield similar photosynthesis responses to light and CO2 may facilitate intercomparison of Earth system and weather models.

Radioactive contamination of seawater has often caused concern, for example about releases from Sellafield and Le Havre and later about the Fukushima disaster. Repeated reporting has contributed to the general feeling that the sea is particularly sensitive to radioactive contamination (Greenpeace,1998). This is not the case, it is rather the opposite. Marine life is much better protected against radioactive contamination than life on land. This protection is due to three natural factors: shielding, dilution and isotope competition.

Any agricultural production process is characterized by input¿output relations. In this paper we show that the production functions of Liebig, Mitscherlich and Liebscher for the relation between nutrient supply and crop production can be regarded as special variants of one 'integrated model'. The model is elaborated for two nutrients, nitrogen and phosphorus, and is based on the Michaelis-Menten hyperbolic equation. This basic equation has two main terms and one multiplicative interaction term. The parameter values determine which one of the aforementioned functions is generated. 'Greenwood's variant of the Michaelis-Menten function' is approached if the main terms dominate. 'De Wit's variant of the Mitscherlich function' is approached if the multiplicative term dominates. Liebig's function emerges from any of these variants if nutrient supply is constrained to such an extent that nutrient uptake continually exhausts the nutrient stock. The 'Liebscher variant' - considered the most appropriate for most empirical situations - is intermediate between those of Liebig, Michaelis-Menten and 'De Wit's Mitscherlich', and can be obtained by parameter calibration. Generally, these functions result in 'decreasing marginal returns' with increasing nutrient supply. However, if interacting nutrients are supplied in precisely the required proportion, the variant with a multiplicative term does show 'increasing marginal returns', but only in conditions of low nutrient supply rates, low nutrient affinities and / or high nutrient losses

During the 20th century hunger has become a problem of poverty amidst plenty rather than absolute food scarcity. The question is whether this will remain so or whether the hunger of the poor will once more be exacerbated by rising food prices. In this paper we discuss biophysical conditions, social forces and non-linear interactions that may critically influence the global availability of food in the long term. Until 2050, the global demand for primary phytomass for food will more than double, while competing claims to natural resources for other purposes (including biobased non-foods) will increase. A sober assessment of the earth¿s biophysical potential for biomass production, which recognizes competing claims and unavoidable losses, suggests that this is in itself still large enough for accommodating this rising demand. However, the exploitation of this biophysical potential proceeds through technical paradigms that set a relative maximum to food production. In addition, socio-economic mechanisms make the food economy run up against a ceiling even before this maximum is reached. As a consequence, current developments may well entail a new trend change in international markets. These developments include the depletion of land and water reserves, the stagnation of the potential yields of major crops, the rise in energy prices, and the way in which systemic socio-economic factors lead to a strong underutilization of production possibilities in the developing world. Given these conditions, the avoidance of steep rises in food prices may depend on the timely relaxation of socio-economic constraints in developing countries and on timely breakthroughs in sustainable yield increases, biorefinement and non-farm production systems. Myopic expectations make it doubtful whether spontaneous market forces will provide the necessary incentives for this, which may be reason for societal actors to consider the need for more active policies

Any agricultural production process is characterized by input-output relations. In this paper we show that the production functions of Liebig, Mitscherlich and Liebscher for the relation between nutrient supply and crop production can be regarded as special variants of one ‘integrated model’. The model is elaborated for two nutrients, nitrogen and phosphorus, and is based on the Michaelis-Menten hyperbolic equation. This basic equation has two main terms and one multiplicative interaction term. The parameter values determine which one of the aforementioned functions is generated. ‘Greenwood’s variant of the Michaelis-Menten function’ is approached if the main terms dominate. ‘De Wit’s variant of the Mitscherlich function’ is approached if the multiplicative term dominates. Liebig’s function emerges from any of these variants if nutrient supply is constrained to such an extent that nutrient uptake continually exhausts the nutrient stock. The ‘Liebscher variant’ – considered the most appropriate for most empirical situations – is intermediate between those of Liebig, Michaelis-Menten and ‘De Wit’s Mitscherlich’, and can be obtained by parameter calibration. Generally, these functions result in ‘decreasing marginal returns’ with increasing nutrient supply. However, if interacting nutrients are supplied in precisely the required proportion, the variant with a multiplicative term does show ‘increasing marginal returns’, but only in conditions of low nutrient supply rates, low nutrient affinities and / or high nutrient losses

Studie naar het veranderenv an het beleid bij ingrijpen bij oevererosie, met name langs de Maas. Rapport bevat ook achterliggende studies, en case studies. Het rapport beoogt de criteria aan te leveren om al dan niet in te grijpen bij spontaan optredende oevererosie, dus niet voor trajecten waar de oeververdediging actief wordt verwijderd! Voorlopig wordt uitgegaan van trajecten waar spontane oevererosie plaatsvindt. Dit is op dit moment ca 6 km in het beheersgebied van de directie Limburg (buiten de Lus van Linne en Grensmaas). Het actief verwijderen van oeververdediging waarvoor nu een aantal proefprojecten lopen (Maaswerken), valt buiten de scope van dit project. Beide projecten zijn wel met elkaar afgestemd. Het rapport is het resultaat van een onderzoeksproject dat door de afdeling ANW in samenwerking met de dienstkringen in de periode 2001-2003 is uitgevoerd1, in het kader van BPN.

If dew formation cannot be measured it has to be estimated. Available simulation models for estimating dew formation require hourly weather data as input. However, such data are not available for places without an automatic weather station. In such cases the diel pattern of weather variables might be used to run the simulation model. To investigate the possibility of using diel patterns of weather variables to estimate dew formation, a field experiment was carried out from February to April 1994 at the International Rice Research Institute (IRRI), Los Baños, Philippines. The seasonally averaged diel patterns of weather variables were derived from hourly records. Both the hourly recorded weather data and the seasonally averaged (‘mean’) diel patterns derived from these weather variables were used to run a simulation model based on an energy-balance approach. Hourly recorded weather data as input gave the best estimation of dew formation at crop height. Substituting the hourly records of wind speed and air temperature by their mean diel patterns gave slightly worse but still acceptable dew estimates, as confirmed by a Wilcoxon signed rank test. This test showed that for water vapour pressure and nocturnal net radiation, however, the substitution of actual values by mean diel patterns resulted in unacceptably large estimation errors.

Studie naar het veranderenv an het beleid bij ingrijpen bij oevererosie, met name langs de Maas. Rapport bevat ook achterliggende studies, en case studies. Het rapport beoogt de criteria aan te leveren om al dan niet in te grijpen bij spontaan optredende oevererosie, dus niet voor trajecten waar de oeververdediging actief wordt verwijderd! Voorlopig wordt uitgegaan van trajecten waar spontane oevererosie plaatsvindt. Dit is op dit moment ca 6 km in het beheersgebied van de directie Limburg (buiten de Lus van Linne en Grensmaas). Het actief verwijderen van oeververdediging waarvoor nu een aantal proefprojecten lopen (Maaswerken), valt buiten de scope van dit project. Beide projecten zijn wel met elkaar afgestemd. Het rapport is het resultaat van een onderzoeksproject dat door de afdeling ANW in samenwerking met de dienstkringen in de periode 2001-2003 is uitgevoerd1, in het kader van BPN.

Keywords: Imaging spectroscopy, imaging spectrometry, remote sensing, reflection, reflectance, grass sward, white clover, recognition, characterisation, ground cover, growth monitoring, stress detection, heterogeneity quantificationThe potential of imaging spectroscopy as a tool for characterisation of grass swards was explored with respect to growth monitoring, detection of nitrogen and drought stress, and assessment of dry matter yield, clover content, nutrient content, feeding value, sward heterogeneity and production capacity. To this end, an experimental imaging spectroscopy system was developed. The system detects reflection in image lines in the wavelength range from 405-1659 nm with three different sensors at 1.3 m above the soil surface. Spectral resolution varies between 5-13 nm, and spatial resolution between 0.28-1.45 mm 2per pixel at the soil. As a result of system design, reflection intensity is a function of leaf height and leaf angle. The system was tested on mini swards grown in containers. For each mini sward, 42 image lines were recorded in a regular sampling pattern per recording event.Five experiments were conducted with Lolium perenne L. and/or Trifolium repens L. mini swards. In these experiments degree of sward damage, level of nitrogen (N) application (two experiments), water supply and white clover content were varied. In the sward damage experiment and in one N experiment light interception was recorded regularly; at harvest, also crop height and canopy reflectance (with a Cropscan) was measured. Mini swards were harvested at a fixed level and in one of the N experiments in three strata. During the experiments, hyperspectral reflectance was recorded 2-4 times per week.Image lines were classified to separate pixels containing soil, dead material and green leaves. These classes were subdivided into reflection intensity classes. Ground cover (GC), reflection intensity, image line texture, spatial heterogeneity and patterns, and spectral chara

A simple method was developed to estimate the fraction radiation intercepted by small eastern white cedar plants (Thuja occidentalis 'Brabant'). The method, which describes the crop canopy as rows of cuboids, was compared with methods used for estimating radiation interception by crops with homogeneous canopies and crops grown in rows. The extinction coefficient k was determined at different plant arrangements and an average k-value of 0.48 ± 0.03 (R2 = 0.89) was used in the calculations. Effects of changing plant characteristics and inter- and intra-row plant distances were explored. The fraction radiation intercepted that was estimated with the method for rows of cuboids was up to 20% and for row crops up to 8% lower than estimated with the method for homogeneous canopies at low plant densities and a LAI of 1. The fraction radiation intercepted by small plants of Thuja occidentals 'Brabant' was best estimated by the simple method described in this paper

RIVM rapport:Abstract niet beschikbaar, Methane (CH4) is a potent greenhouse gas. Wetland rice fields constitute one of the major anthropogenic CH4 sources but the source strength is surrounded by a large uncertainty. The work presented in this report aims at reducing the uncertainty in emissions from wetland rice fields by making independent estimates of regional CH4 source strengths: "up-scaling" from the soil-rice ecosystem perspective and "down-scaling" from the atmosphere perspective. Case studies in Java and the Philippines described the upscaling from point to regional scale, the Chinese case study focused on the regional to national scale. A process-based field scale model for CH4 emissions from rice paddies was made, validated and coupled to a Geographic Information System to scale up regional CH4 emissions from rice paddies. Potential land use changes for Java and China were quantified with a land use change model and predicted changes were evaluated using the CH4 emission model, proxy methods and emission factors. Simultaneously, trend analysis of rice field emissions indicates that (1) rice yield increases have usually not resulted in increased methane emissions per unit of harvested area and, (2) global annual emission from rice fields may be considerably lower than generally assumed, partly because of recent decreases in the use of organic amendments. Rice agriculture is a dynamic activity, economical changes and technological advances influenced the emission levels and will continue to do so. This makes fixing the CH4 source strength of rice paddies difficult and increases uncertainties. Downscaling from the global scale to regional scale was pursued by inverse modelling of the sources and sinks of atmospheric CH4. Improvements were made in the availability of measurements and a priori information, the accuracy of the atmospheric transport model, and the applied inverse modeling technique. Constraining the global rice CH4 source using inverse modelling, was explored by comparing a standard

niet beschikbaar, Methane (CH4) is a potent greenhouse gas. Wetland rice fields constitute one of the major anthropogenic CH4 sources but the source strength is surrounded by a large uncertainty. The work presented in this report aims at reducing the uncertainty in emissions from wetland rice fields by making independent estimates of regional CH4 source strengths: "up-scaling" from the soil-rice ecosystem perspective and "down-scaling" from the atmosphere perspective. Case studies in Java and the Philippines described the upscaling from point to regional scale, the Chinese case study focused on the regional to national scale. A process-based field scale model for CH4 emissions from rice paddies was made, validated and coupled to a Geographic Information System to scale up regional CH4 emissions from rice paddies. Potential land use changes for Java and China were quantified with a land use change model and predicted changes were evaluated using the CH4 emission model, proxy methods and emission factors. Simultaneously, trend analysis of rice field emissions indicates that (1) rice yield increases have usually not resulted in increased methane emissions per unit of harvested area and, (2) global annual emission from rice fields may be considerably lower than generally assumed, partly because of recent decreases in the use of organic amendments. Rice agriculture is a dynamic activity, economical changes and technological advances influenced the emission levels and will continue to do so. This makes fixing the CH4 source strength of rice paddies difficult and increases uncertainties. Downscaling from the global scale to regional scale was pursued by inverse modelling of the sources and sinks of atmospheric CH4. Improvements were made in the availability of measurements and a priori information, the accuracy of the atmospheric transport model, and the applied inverse modeling technique. Constraining the global rice CH4 source using inverse modelling, was explored by comparing a standard

RIVM rapport:Abstract niet beschikbaar, Methane (CH4) is a potent greenhouse gas. Wetland rice fields constitute one of the major anthropogenic CH4 sources but the source strength is surrounded by a large uncertainty. The work presented in this report aims at reducing the uncertainty in emissions from wetland rice fields by making independent estimates of regional CH4 source strengths: "up-scaling" from the soil-rice ecosystem perspective and "down-scaling" from the atmosphere perspective. Case studies in Java and the Philippines described the upscaling from point to regional scale, the Chinese case study focused on the regional to national scale. A process-based field scale model for CH4 emissions from rice paddies was made, validated and coupled to a Geographic Information System to scale up regional CH4 emissions from rice paddies. Potential land use changes for Java and China were quantified with a land use change model and predicted changes were evaluated using the CH4 emission model, proxy methods and emission factors. Simultaneously, trend analysis of rice field emissions indicates that (1) rice yield increases have usually not resulted in increased methane emissions per unit of harvested area and, (2) global annual emission from rice fields may be considerably lower than generally assumed, partly because of recent decreases in the use of organic amendments. Rice agriculture is a dynamic activity, economical changes and technological advances influenced the emission levels and will continue to do so. This makes fixing the CH4 source strength of rice paddies difficult and increases uncertainties. Downscaling from the global scale to regional scale was pursued by inverse modelling of the sources and sinks of atmospheric CH4. Improvements were made in the availability of measurements and a priori information, the accuracy of the atmospheric transport model, and the applied inverse modeling technique. Constraining the global rice CH4 source using inverse modelling, was explored by comparing a standard

RIVM rapport:Abstract niet beschikbaar, Methane (CH4) is a potent greenhouse gas. Wetland rice fields constitute one of the major anthropogenic CH4 sources but the source strength is surrounded by a large uncertainty. The work presented in this report aims at reducing the uncertainty in emissions from wetland rice fields by making independent estimates of regional CH4 source strengths: "up-scaling" from the soil-rice ecosystem perspective and "down-scaling" from the atmosphere perspective. Case studies in Java and the Philippines described the upscaling from point to regional scale, the Chinese case study focused on the regional to national scale. A process-based field scale model for CH4 emissions from rice paddies was made, validated and coupled to a Geographic Information System to scale up regional CH4 emissions from rice paddies. Potential land use changes for Java and China were quantified with a land use change model and predicted changes were evaluated using the CH4 emission model, proxy methods and emission factors. Simultaneously, trend analysis of rice field emissions indicates that (1) rice yield increases have usually not resulted in increased methane emissions per unit of harvested area and, (2) global annual emission from rice fields may be considerably lower than generally assumed, partly because of recent decreases in the use of organic amendments. Rice agriculture is a dynamic activity, economical changes and technological advances influenced the emission levels and will continue to do so. This makes fixing the CH4 source strength of rice paddies difficult and increases uncertainties. Downscaling from the global scale to regional scale was pursued by inverse modelling of the sources and sinks of atmospheric CH4. Improvements were made in the availability of measurements and a priori information, the accuracy of the atmospheric transport model, and the applied inverse modeling technique. Constraining the global rice CH4 source using inverse modelling, was explored by comparing a standard

A fully mechanistic model based on diffusion equations for gas transport in a flooded rice system is presented. The model has transport descriptions for various compartments in the water-saturated soil and within the plant. Plant parameters were estimated from published data and experiments independent of the validation experiment. An independent experiment is described in which the diffusion coefficient of sulfurhexafluoride (SF6) in water-saturated soil was determined. The model was validated by experiments in which transport of SF6 through soil and plant was monitored continuously by photoacoustics. The independent default settings could reasonably predict gas release dynamics in the soil-plant system. Calculated transmissivities and concentration gradients at the default settings show that transport within the soil was the most limiting step in this system, which explains why most gases are released via plant-mediated transport. The root-shoot interface represents the major resistance for gas transport within the plant. A sensitivity analysis of the model showed that gas transport in such a system is highly sensitive to the estimation of the diffusion coefficient of SF6, which helps to understand diel patterns found for greenhouse gas emissions, and to the root distribution with depth. This can be understood from the calculated transmissivities. The model is less sensitive to changes in the resistance at the root-shoot interface and in the root fraction active in gas exchange. The model thus provides an understanding of limiting steps in gas transport, but quantitative predictions of in situ gas transport rates will be difficult given the plasticity of root distribution.

RIVM rapport:Abstract niet beschikbaar, The integrated nitrous oxide (N2O) and methane (CH4) grassland project aims to estimate and explain emissions of these greenhouse gases from two ecosystems, namely drained agricultural peat soil under grass at the experimental farm Zegveld and undrained peat in the nature preserve Nieuwkoopse Plassen. Peat soils were chosen because of their expected considerable contribution to the greenhouse gas budget considering the prevailing wet and partial anaerobic conditions. The emission dynamics of these ecosystems are considered representatives of large peat areas because the underlying processes are rather general and driven by variables like organic matter characteristics, water and nutrient conditions and type of vegetation. The research approach comprises measerements and modelling at different integration levels relating to the microbiology of the production and consumption of N2O and CH4 (laboratory studies), their movement through peat soil (rhizolab and field studies), and the resulting fluxes (field studies). Typical emissions from drained soil were 15-40 kg ha-1 y-1 N2O and virtually zero for CH4. The undrained soil in the nature preserve emitted 100-280 kg ha-1 y-1 CH4, and probably little N2O. The process knowledge collected and partly integrated in the models helps to explain these data. For example, the low methane emissions from drained peat can more coherently be understood and extrapolated because (i) upper soil layers are aerobic, thus limiting methane production and stimulating methane oxidation, (ii) absence of aerenchymatous roots of wetland plants that connect deeper anaerobic soil layers where methane is produced to the atmosphere and supply labile carbon, (iii) a low methane production potential in deep layers due to the low decomposability of organic matter, and (iv) long anaerobic periods needed in the topsoil to develop a methane production potential.

RIVM rapport:Abstract niet beschikbaar, The integrated nitrous oxide (N2O) and methane (CH4) grassland project aims to estimate and explain emissions of these greenhouse gases from two ecosystems, namely drained agricultural peat soil under grass at the experimental farm Zegveld and undrained peat in the nature preserve Nieuwkoopse Plassen. Peat soils were chosen because of their expected considerable contribution to the greenhouse gas budget considering the prevailing wet and partial anaerobic conditions. The emission dynamics of these ecosystems are considered representatives of large peat areas because the underlying processes are rather general and driven by variables like organic matter characteristics, water and nutrient conditions and type of vegetation. The research approach comprises measerements and modelling at different integration levels relating to the microbiology of the production and consumption of N2O and CH4 (laboratory studies), their movement through peat soil (rhizolab and field studies), and the resulting fluxes (field studies). Typical emissions from drained soil were 15-40 kg ha-1 y-1 N2O and virtually zero for CH4. The undrained soil in the nature preserve emitted 100-280 kg ha-1 y-1 CH4, and probably little N2O. The process knowledge collected and partly integrated in the models helps to explain these data. For example, the low methane emissions from drained peat can more coherently be understood and extrapolated because (i) upper soil layers are aerobic, thus limiting methane production and stimulating methane oxidation, (ii) absence of aerenchymatous roots of wetland plants that connect deeper anaerobic soil layers where methane is produced to the atmosphere and supply labile carbon, (iii) a low methane production potential in deep layers due to the low decomposability of organic matter, and (iv) long anaerobic periods needed in the topsoil to develop a methane production potential.

RIVM rapport:Abstract niet beschikbaar, The integrated nitrous oxide (N2O) and methane (CH4) grassland project aims to estimate and explain emissions of these greenhouse gases from two ecosystems, namely drained agricultural peat soil under grass at the experimental farm Zegveld and undrained peat in the nature preserve Nieuwkoopse Plassen. Peat soils were chosen because of their expected considerable contribution to the greenhouse gas budget considering the prevailing wet and partial anaerobic conditions. The emission dynamics of these ecosystems are considered representatives of large peat areas because the underlying processes are rather general and driven by variables like organic matter characteristics, water and nutrient conditions and type of vegetation. The research approach comprises measerements and modelling at different integration levels relating to the microbiology of the production and consumption of N2O and CH4 (laboratory studies), their movement through peat soil (rhizolab and field studies), and the resulting fluxes (field studies). Typical emissions from drained soil were 15-40 kg ha-1 y-1 N2O and virtually zero for CH4. The undrained soil in the nature preserve emitted 100-280 kg ha-1 y-1 CH4, and probably little N2O. The process knowledge collected and partly integrated in the models helps to explain these data. For example, the low methane emissions from drained peat can more coherently be understood and extrapolated because (i) upper soil layers are aerobic, thus limiting methane production and stimulating methane oxidation, (ii) absence of aerenchymatous roots of wetland plants that connect deeper anaerobic soil layers where methane is produced to the atmosphere and supply labile carbon, (iii) a low methane production potential in deep layers due to the low decomposability of organic matter, and (iv) long anaerobic periods needed in the topsoil to develop a methane production potential.

This thesis describes model development and experimentation on the comprehension and prediction of methane (CH 4 ) emissions from rice paddies. The large spatial and temporal variability in CH 4 emissions and the dynamic non-linear relationships between processes underlying CH 4 emissions impairs the applicability of empirical relations. Mechanistic concepts are therefore starting point of analysis throughout the thesis.The process of CH 4 production was investigated by soil slurry incubation experiments at different temperatures and with additions of different electron donors and acceptors. Temperature influenced conversion rates and the competitiveness of microorganisms. The experiments were used to calibrate and validate a mechanistic model on CH 4 production that describes competition for acetate and H 2 /CO 2 , inhibition effects and chemolithotrophic reactions. The redox sequence leading eventually to CH 4 production was well predicted by the model, calibrating only the maximum conversion rates.Gas transport through paddy soil and rice plants was quantified by experiments in which the transport of SF 6 was monitored continuously by photoacoustics. A mechanistic model on gas transport in a flooded rice system based on diffusion equations was validated by these experiments and could explain why most gases are released via plant mediated transport. Variability in root distribution led to highly variable gas transport.Experiments showed that CH 4 oxidation in the rice rhizosphere was oxygen (O 2 ) limited. Rice rhizospheric O 2 consumption was dominated by chemical iron oxidation, and heterotrophic and methanotrophic respiration. The most abundant methanotrophs and heterotrophs were isolated and kinetically characterised. Based upon these experiments it was hypothesised that CH 4 oxidation mainly occurred at microaerophilic, low acetate conditions not very close to the root surface. A mechanistic rhizosphere model that combined production and consumption of O 2

Eddy correlation measurements of CO2 exchange were made in intensively managed peat pastures at 2 different groundwater tables during most of a growing season. F was separated into a respiratory and an assimilatory CO2 flux. The fit of the Arrhenius temperature response to Fr showed that Fr was generally higher at low groundwater tables. The fit of a hyperbolic irradiance response to Fa showed that Fa was also generally higher at low groundwater tables, more than compensating for higher Fr. The daily CO2 balance suggested that the low groundwater pasture was a larger CO2 sink or a smaller CO2 source than the high groundwater pasture during the measurement period. The difference in Fr between the groundwater tables was substantially less than the factor 2 difference in level of soil subsidence. This suggests that oxidization of soil organic matter was a relatively minor factor in soil subsidence.

Introduction and objectivesGood comprehension of the energy and mass cycles and their effect on climate dynamics is crucial to understanding, predicting and anticipating ecological changes due to possible future climate perturbations. Here direct and long-term flux density measurements of greenhouse gases from various ecosystems provide means to supply such fundamental knowledge. For the global water vapour and carbon cycles, however, the interactions between different spatial scales become important, where extrapolating from canopy flux density measurements to global budgets lead to practical and theoretical problems. This thesis focuses on the direct and long-term measurement of surface flux densities and interaction processes at the canopy (< 1 km scale within the framework of the Surface Layer Integration Measurements and Modelling (SLIMM) project. Furthermore, some characteristics and limitations of the scintillation technique are studied in two field experiments in New Zealand.As indicated in Chapter 1, the first objective of this project was the direct and continuous long-term measurement of the surface flux densities of radiation, momentum, heat, water vapour and carbon dioxide (CO 2 ) to study the effect of biological and climatic processes that regulate carbon dioxide exchange of this ecosystem at the canopy scale. At the same time these data were used to study the effect of plant related and environmental conditions on the interaction of carbon dioxide and water vapour exchange, to satisfy the second objective of the thesis. The third objective focussed on the prospect of obtaining both the spatial averaged sensible heat flux density and momentum flux density from scintillation measurements.Generally, a compromising point measurement of the mean horizontal wind speed or friction velocity is used to calculate the sensible heat flux density from the temperature structure parameter. By using two scintillometers at two heights, point measurements to obtain th

The study described in this thesis focuses on the understanding of growth of leaf area and biomass in wheat and sunflower under low phosphorus conditions.Chapters 2 and 3 address the question whether P-deficiency limits leaf area expansion directly by inhibiting the individual leaf expansion, or through its effects on the availability of assimilates for growth. Experimental and simulation techniques were used to find an answer to this question. It was concluded that in sunflower the effects of P on sink size and assimilate supply were important for determining plant leaf area expansion (Chapter 2). Instead, wheat responded to a low P supply mainly by reducing sink size (Chapter 3). A sensitivity analysis of the effects of different model parameters at different levels of P supply, on the simulated total leaf area, showed that the value of the phyllochron, in wheat and sunflower, and tillering in wheat were crucial in determining the total leaf area.Chapter 4 focuses on the effects of P on the generation of leaves and tillers in wheat. Here, it was shown that the emergence of main stem leaves in wheat plants grown under P-deficient conditions was delayed (higher phyllochron) as both, the rate of leaf primordia initiation in the apex, and the rate of individual leaf expansion were reduced.In Chapter 5, the effects of P and assimilate supply on tillering were studied in a field experiment. P deficiencies directly altered the normal pattern of tiller emergence by slowing down the emergence of leaves on the main stem, and by reducing the maximum rate of tiller emergence. In general terms, assimilate supply seemed to play a minor role determining tillering. Including the effects of P on the phyllochron and on the maximum tillering rate in a morphogenetic model of the generation of leaves and tillers, it was possible to explain the dynamics of tiller emergence of a field experiment.In Chapter 6, a comparative study of the response to P in wheat and sunflower is presented.

For a long time, the emphasis in silviculture in Western Europe was solely on even-aged, monospecific stands; many empirical stand-level growth models were developed and successfully used for managing such stands. In contrast, no generally accepted growth and yield approach has emerged so far for mixed forests. Moreover, the inexhaustible number of species combinations, management regimes, and site-dependent interactions make an empirical approach less suitable.In the present study, a mechanistic model was developed that simulates growth and yield in mixed forest stands. Douglas-fir ( Pseudotsuga menziesii (Mirb.) Franco) and beech ( Fagus sylvatica L.) were used in this research. In the model, tree growth is dependent on radiation availability. Stand development is largely driven by competition for radiation. A spatial module was developed to investigate the effects of tree and stand characteristics on radiation interception. The study showed that in heterogeneous stands a spatial approach is needed to account for competition between trees.Growth of the trees was estimated using the radiation-use efficiency concept (RUE). Results revealed that detailed process models can be used to estimate RUE and that it is a suitable tool for (mixed) forest modelling.To describe the distribution of the dry matter growth, a separate module was developed using functional relationships between tree components: the dry matter distribution is driven by the aim to maintain structural balances within the tree. The study showed that this approach is able to reproduce the development of an individual forest tree. The approach was thus considered very suitable for modelling the effects of between-tree competition for resources on growth and development of mixed forest stands.The overall growth model, COMMIX, was applied to investigate the effects of stand composition on mixed stand productivity, using a replacement series. Analysis showed that the productivity of mixed forest stands is ge

This thesis represents detailed research on the "rice-soils-weather" system of the Ebro Delta (Spain) providing knowledge on how temperature, radiation, soil properties and farm management determine rice growth. After an introductory chapter, the findings are developed step-by-step. (i) Chapter 2 is an overview of the conditions in the study area. (ii) Chapter 3 focuses on the study of the soils creating a soil geographic database of the northern part of the Ebro Delta. Four properties were used for defining soil units; soil development, drainage status, texture and salinity. (iii)Chapters 4 and 5 deal with rice growth under weather limited conditions. Potential productions of 13000 kg ha -1were estimated, while maximum yields of 11000 kg ha -1were recorded at field level. In Chapter 4, the phenological development, the daily dry matter production and the leaf area development of the rice crop were modelled. In Chapter 5, the use of remote sensing techniques at field level for monitoring the rice crop status were tested. (iv)Chapters 6 and 7 analyze rice growth in relation to soil properties and farm management. Two soil factors were found to dominate the effects on yield: one was topsoil CEC (in strong association with clay content) with a positive effect, and the other one was soil salinity with a negative effect. High groundwater tables did not have significant effects on rice yield, except when the water had a high salt content. Four main groups of causes within the cropping status limited rice growth: potassium and zinc shortage where a strong antagonism of either factor with sodium was observed, low plant establishment where a minimum number of 160-180 plants m -2was necessary to maximize yield, and length of the growing season, especially the length of the pre-heading period in which the potential size of the crop was primarily determined.Potassium and zinc shortages in the plant were mainly induced by soil salinity. High K in saline soils did not increase K

The study described in this thesis focuses on a quantification of leaf wetness formation in paddy rice crops based on insight in the physical processes of the formation of leaf wetness. For this purpose, experimental research was conducted in a tropical paddy rice field.A shielding (nocturnal net radiative loss) experiment was designed to investigate the dependence of dew formation on nocturnal net radiative loss. A simple method was developed to estimate dew amount and duration using the nightly total net radiative loss. The shielding experiment unexpectedly provided a feasible method for experimentally distinguishing dew from guttation. For a better understanding of the characteristics of the formation of leaf wetness in paddy rice crops, warm water flooding both in the paddy rice field and in a phytotron was conducted to investigate the effects of water temperature on dew formation and guttation. The experimental data indicated an optimum paddy water temperature of 30°C for rice leaf guttation. The effect of water temperature on dew formation depended on the weather condition above the canopy, especially the thermal stratification condition, net radiation and vapour pressure deficit. A simple device, the dewball, was designed to observe dew formation and to determine its threshold value of nocturnal net radiative loss from top leaves. This was shown to be a simple and accurate method for estimating daily dew duration on top leaves. The possibility of using the mean diurnal patterns of weather variables to estimate dew formation was analysed by comparing the dew estimated using a simulation model to the measured results. This helped to understand to what extent the diurnal patterns will give as good an estimate of dew formation as when the observed hourly weather data are used. Based on the observation results on the dewball and the results of the shielding experiment, a simple approach to estimate daily dew duration on top leaves of the paddy rice crops was formu