Evapotranspiration modules for crop growth simulation. Implementation of the algorithms from Penman, Makkink and Priestley-Taylor

Calculation of evapotranspiration is essential for the estimation of crop water use or for studying the effect of drought stress on crop performance with simulation models. Several methods are available for calculation of evapotranspiration. This report describes three different methods : the Penman method (1948) and the approaches of Makkink (1957) and Priestley -Taylor (1972). The modules described in this report are developed for use in general crop growth models for water-limited conditions, such as in Van Laar et al. (1992). The application of the modules, however, is not limited to the SUCROS type models

The possible effects of climate change on the spatial and temporal variation of the altitudinal temperature gradient and the consequences for growth potential in the uplands of northern England

This thesis studies the potential impacts of lapse rate changes on the altitudinal thermal resource gradient in Northern England and hence of climate change on upland climate. The extreme marginality of the Pennine uplands in terms of climatic potential for plant growth is explained by reference to the maritime climate. Because the ground-based temperature lapse rate controls the altitudinal thermal resource gradient, the variation of daily temperature lapse rates by season and airflow is described, using 22 stations ranging from 8 to 847 metres above sea-level. Multiple regression models developed for each airflow in each month successfully describe surface temperature variation in most cases. Such models are used as a basis upon which to describe altitudinal variations in growing season parameters such as accumulated temperatures and frost frequency, for the present climate. Airflow scenarios, based on the regression models, describe the effects of changes in relative frequencies of airflow patterns. The altitudinal gradient in, and absolute values of, growing season parameters depend strongly on relative frequencies of Atlantic westerlies and more blocked conditions. Assuming the annual l000 dºC (degree-day) isotherm to represent the altitudinal limit to agricultural cultivation, individual annual elevations between 1801 and 1990 vary by over 300 metres. Extreme sensitivity to the circulatory pattern is also illustrated. Effects of temperature variability within airflows are at least as strong as those of mean conditions in many cases. The use of General Circulation Model output (UKHI 2 times C0(_2)) leads to strong changes in climatic potential. For example, few areas retain an annual temperature accumulation below 1000 dºC. Changes in frost parameters are also marked. Other climatic and non-climatic factors would have to be considered to predict land-use change. Preliminary analysis suggests that changes in other climatic elements (e.g. windiness or precipitation) will complement the effects of a temperature increase

Phenology and growth of European trees in relation to climate change

Research topicsThe relationships between climate and both phenology and growth of some important European tree species were studied to evaluate the potential impacts of climate change on trees and forests in Europe. In order to make such assessments, insight is required on the mechanisms how climatic variables interact with plant processes. The topics addressed in this study were: (1) the modelling of phenology, (2) the consequences of climate change on spring frost damage, (3) the importance of phenotypic plasticity, (4) the importance of phenology on the effects of climate change on growth of monospecies deciduous forests, and (5) the importance of phenology on the effects of climate change on growth of mixed-species deciduous forests.Modelling phenologyTo evaluate the impacts of climate change on growth of temperate deciduous tree species, the onset and cessation of the growth must be accurately described. A review is presented on eight models predicting the date of leaf unfolding depending on temperature. These models were fitted using 57 years of observations on the date of leaf unfolding of Fagus sylvatica in The Netherlands, and used to predict 40 years of similar observations collected in Germany. As conflicting experimental evidence exist on the role of photoperiod on leaf unfolding of Fagus sylvatica, photoperiod was incorporated into each of these models.The timing of leaf unfolding could best be described by a model in which the effects of chilling temperatures (-5 to +10°C) and forcing temperatures (>0°C) operate sequentially in time, according to a triangular and logistic function, respectively. Including photoperiod reduced the predicting power of this model.Spring frost damageTwo studies presented in literature evaluate the effect of increasing winter temperature on the probability of spring frost damage to trees. However, one study predicted an increase, while the other predicted a decrease in the probability of spring frost damage. It is unclear whether the disparity is because: (1) different models were used, (2) different climatic warming scenarios used, or (3) the tree species at the different locations respond differently to warmer winters. To evaluate the effects of climatic warming to Larix decidua, Betula pubescens, Tilia platyphylla, Fagus sylvatica, Tilia cordata, Quercus rubra, Quercus robur, Fraxinus excelcior, Quercus petraea, Picea abies and Pinussylvestris in The Netherlands and in Germany, both models were fitted to long series of observations on the date of leaf unfolding of these tree species. The impact of the two scenarios (uniformly and non-uniformly changing winter temperature) on the date of leaf unfolding and on the probability of freezing temperature around that date was evaluated. To test the importance of adaptation to local climate, hypothetical provenance transfers were analysed.For tree species in The Netherlands and Germany the probability of spring frost damage will decrease, provided the variability in temperature does not change. The contradictory results found in literature could be ascribed to differences among provenances adapted to their local climate, rather than to differences between either the models or the climatic warming scenarios used in these studies.PlasticityTo evaluate the potential response of individual trees to climatic warming, phenological observations of clones of Larix decidua, Betula pubescens, Tilia cordata, Populus canescens, Quercus robur, Fagus sylvatica, and Picea abies transferred over a large latitudinal range in Europe were analysed. The magnitude of the clone's response was compared to that of genetically different trees of the same species along a part of the latitudinal range, which were assumed to have adapted to their local climate.The responses of the date of leaf unfolding and leaf fall of the clones to temperature are similar in magnitude to those of the genetically different trees. This demonstrates that trees possess a considerable plasticity and are able to respond phenotypically to a major change in their local climate. For the clones of Larix decidua and Quercus robur the growing season may shorten with increasing temperature, because leaf fall is advanced more than leaf unfolding. In Betula pubescens and Populus canescens, leaf unfolding and leaf fall are advanced equally, whereas in Tilia cordata and Fagus sylvatica the date of leaf fall seems to be unaltered but leaf unfolding advances with increasing temperature. These differences in the duration of the growing season in response to increasing temperature may alter the competitive balance between the species in mixed stands.Descriptive dynamic models showed that most of the variance of the date of leaf unfolding can be accounted for by temperature. However, a generally applicable model of leaf fall based on temperature and/or photoperiod could not improve the null model, i.e. the mean date of leaf fall, because of variability in other environmental factors.The lowest temperature around the date of leaf unfolding and leaf fall differed among the clones. The hypothesis that the survival of the clones is curtailed by spring frosts was supported. Thus, these lowest temperatures around leaf unfolding may represent thresholds below which the species cannot survive.It is argued that these thresholds may be a particularly sensitive means to evaluate the impacts of climatic warming on the geographical distribution of tree species.Growth of monospecies forestsThe importance of three phenological types of deciduous tree for the effects of climate change on growth of monospecies forests was evaluated using the model FORGRO. The climate change scenarios used were a doubling of the C02 concentration (700 μmol mol -1) and an increase in temperature ranging from 0 to 7°C. To elucidate the relative importance of photosynthesis and allocation for this evaluation, models with different levels of mechanistic detail of photosynthesis and allocation were used. The photosynthesis approach of FORGRO was compared to the Farquhar and Von Caernmerer approach as formulated in PGEN (FORGRO-PGEN). Similarly, the allocation approach of FORGRO was compared to the transport-resistance approach, as formulated in the ITE-Edinburgh model (ITE-FORGRO). A sensitivity analysis was performed to ascertain whether the response of gross photosynthesis to a climate change scenario depends on the value assigned to parameters in these models, and to compare this sensitivity with the differences found between the phenological types. The differences in the response of annual gross photosynthesis ( Pg,a ) to the climate change scenarios between the phenological types were smaller according to ITE- FORGRO as compared to FORGRO. These differences are of a similar magnitude when comparing the two photosynthesis models. Furthermore, FORGRO-PGEN showed that the response of Pg,a to a 2 x [ 2 CO ] increases with rising temperature, thus compensating for the increase in respiration. For both FORGRO and ITEFORGRO, this C0 2 and temperature interaction was not found. Consequently, in these models the increase in respiration exceeded the increase in gross photosynthesis at the higher range of temperature rise. The sensitivity analysis showed that the models differ in the sensitivity of the response of Pg,a to a 2 x [C 2 O ] scenario combined with a temperature rise of 2°C ( C700 / T2 ), when parameter values change by ±25%. In FORGRO-PGEN, the magnitude of the response of Pg,a depended on the values of some of its parameters, especially those determining the Michaelis-Menten kinetics of Rubisco, which for these parameters exceeded the differences between the phenological types in this scenario. In both FORGRO and ITE-FORGRO, this sensitivity is similar to or less than the difference between the phenological types in the C700 / T2 scenario.Growth of mixed-species forestsUsing the same three phenological types and climate change scenarios, the effects of differences in phenology and spring frost damage on growth in mixed-species stands were evaluated using the models FORGRO and HYBRID. FORGRO highlights potential growth in managed forests, whereas HYBRID highlights feedbacks of carbon, water and nitrogen cycles in General Vegetation Types, based on gap model theory. Furthermore, the importance of inaccuracy of the phenological model for growth in mixed-species stands was evaluated by comparing the modelling approach with a regression approach.The results of the climate change scenarios indicate for both FORGRO and HYBRID that: (1) the differences in NPP of the three phenological types considered are enhanced when grown in a mixed-species stand compared to a monospecies stand; and (2) the consequences of frost damage on growth is more prominent in mixed-species stands than in monospecies stands.Considering the accuracy of the modelling approach compared to the regression approach for the timing of leaf unfolding and spring frost damage, the sequential model of leaf unfolding shows a similar response of the NPP as the regression approach, both for the monospecies and the mixed-species situation. The modelling approach yields, however, larger differences in the NPP between the phenological types because the model predicts a greater advancement of leaf unfolding than the regression model. Comparing the regression approach to the modelling approach for frost hardiness, the regression approach shows a greater frequency of frost damage, because according to the model, the minimum level of frost hardiness is attained after the date of leaf unfolding, thus reducing this frequency.The differences in phenological response to temperature can be used to evaluate the consequences of climate change on the geographical distributions of species

Spatial crop and soil landscape processes under special consideration of relief information in a loess landscape

[no abstract

Modelling the Spatial Variation in Alopecurus myosuroides for Precision Weed Management

Alopecurus myosuroides Huds. (black-grass) grows in patches within fields. This presents an opportunity for site-specific management by patch spraying. Despite the economic and environmental benefits of this type of management, it is not being readily taken up by farmers, largely due to the risk of missing weeds that fall outside of established patches. I focus on the environmental determinants of patch location in A. myosuroides and the scale-dependence of relationships between A. myosuroides and environmental properties. Understanding these relationships allowed me to determine which abiotic factors can be used to identify A. myosuroides vulnerable zones within fields and if these relationships occur at scales appropriate for management. This presents a more conservative approach than patch spraying according to observations of previous years’ infestations, as a greater area of the field is sprayed, yet the overall use of pesticide is still reduced. By combining field work, pot experiments, and modelling, I discovered that soil organic matter, water, and pH, amongst other environmental properties, show strong scale-dependent relationships with the within-field distribution of A. myosuroides. These relationships between A. myosuroides and soil properties were often strongest at coarse scales making them particularly useful for the implementation of management practices, which are often limited to coarse-scale implementation by the available machinery. The effects of these soil properties on A. myosuroides are both direct (affecting the plant’s life-cycle) and indirect (altering herbicide efficacy). The incremental changes I observed to different aspects of the life-cycle due to soil properties may seem too small to be of consequence when studied independently, yet when combined in a modelling approach their additive nature revealed them as important determinants of the within-field distribution of this species and the coarse-scale relationships observed in the field are an emergent property of the model

Modelling crop-weed interactions.

Competition between plants for the capture of the essential resources for plant growth (i.e. light, water and nutrients) determines the performance of both natural and agricultural ecosystems. The topic has been studied extensively by ecologists and physiologists, leading to the development of several approaches to describe the outcome of competition. This book reviews these modelling approaches and their potential for predicting yield loss as a result of crop-weed competition. The authors provide a detailed description of the model INTERCOM and of methods to parameterize and evaluate the model using experimental data. Examples are given of how the model can be used to understand the effects of weeds on crops in field situations

Modelling the spatial variation in Alopecurus myosuroides for precision weed management

Alopecurus myosuroides Huds. (black-grass) grows in patches within fields. This presents an opportunity for site-specific management by patch spraying. Despite the economic and environmental benefits of this type of management, it is not being readily taken up by farmers, largely due to the risk of missing weeds that fall outside of established patches. I focus on the environmental determinants of patch location in A. myosuroides and the scale-dependence of relationships between A. myosuroides and environmental properties. Understanding these relationships allowed me to determine which abiotic factors can be used to identify A. myosuroides vulnerable zones within fields and if these relationships occur at scales appropriate for management. This presents a more conservative approach than patch spraying according to observations of previous years’ infestations, as a greater area of the field is sprayed, yet the overall use of pesticide is still reduced. By combining field work, pot experiments, and modelling, I discovered that soil organic matter, water, and pH, amongst other environmental properties, show strong scale-dependent relationships with the within-field distribution of A. myosuroides. These relationships between A. myosuroides and soil properties were often strongest at coarse scales making them particularly useful for the implementation of management practices, which are often limited to coarse-scale implementation by the available machinery. The effects of these soil properties on A. myosuroides are both direct (affecting the plant’s life-cycle) and indirect (altering herbicide efficacy). The incremental changes I observed to different aspects of the life-cycle due to soil properties may seem too small to be of consequence when studied independently, yet when combined in a modelling approach their additive nature revealed them as important determinants of the withinfield distribution of this species and the coarse-scale relationships observed in the field are an emergent property of the model