Browsing by Subject "Energy balance"

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Comparative performance of annual and perennial energy cropping systems under different management regimes
(2007) Böhmel, Ute Constanze; Claupein, Wilhelm
The theme of this thesis was chosen against the background of the necessary substitution of fossil fuels and the need to reduce greenhouse gas emissions. One major solution for these topics may be the energy generation from domestically produced biomass. The overall aim of this thesis was the identification of one or more efficient energy cropping systems for Central Europe. The target was set to supply high quality biomass for existent and currently developing modern conversion technologies. Renewable energy production is thought to be environmentally benign and socially acceptable. The existence of diverse production environments necessitates further diversification and the identification of several energy crops and the development of energy cropping systems suited to those diverse environments. This thesis starts with an introductory essay (chapter 1), which provides the background for renewable energy production, its features, demands and potentials, and the scientific basis of this thesis. Chapters 2 to 6 consist of five manuscripts to be published in reviewed journals (Papers I, II, IV and V) or in a multi-author book (Paper III). Subsequently, the results from all papers are discussed in a general setting (chapter 7), from which a general conclusion is formulated (chapter 8). The basis of the research formed four field experiments, which were conducted at the experimental sites Ihinger Hof, Oberer Lindenhof and Goldener Acker of the University of Hohenheim, in south-western Germany. Paper I addresses the overall objective of this thesis. Selected cropping systems for this experiment were short rotation willow, miscanthus, switchgrass, energy maize and two different crop rotation systems including winter oilseed rape, winter wheat and winter triticale with either conventional tillage or no-till. The systems were cultivated with three different nitrogen fertilizer applications. An energy balance was calculated to evaluate the biomass and energy yields of the different cropping systems. Results indicate that perennial lignocellulosic crops combine high biomass and net energy yields with low input and potential ecological impacts. Switchgrass, which produced low yields at the study site, may better perform on marginal sites. Switchgrass is an example of the need to grow site-adapted energy crops. The annual energy crop maize required the highest input, but at the same time yielded the most. The two crop rotation systems did not differ in yield and energy input, but the system with no-till may be more environmentally benign as it has the potential to sequester carbon. The objective of Paper II was the optimization of crop cultivation through the differentiation of input parameters to enhance the quality of the energy crop triticale, without influencing the biomass yield. The intention was to minimize the content of combustion-disturbing elements (potassium and chlorine) and the ash residue of both aboveground plant parts (grain and straw). It was done through different straw and potassium fertilizer treatments. It could be shown that the removal of straw from the previously cultivated crop and no additional potassium fertilizer could reduce the amount of combustion-disturbing elements. A high influence must also be expected from site and weather conditions. Papers III to V address the supply of different high quality biomasses, with the focus on maize for anaerobic digestion. The objective of Paper III was the assessment of the requirements of biogas plants and biomass for anaerobic digestion. It introduces potential energy crops, along with their advantages and disadvantages. Alongside maize, many other biomass types, which are preserved as silage and are high in carbohydrates and low in lignocelluloses, can be anaerobically digested. The development of potential site-specific crop rotation systems for biomass production are discussed. The objective of Papers IV and V was the identification of suitable biomass and production systems for the anaerobic digestion. The focus lay on the determination of (i) suitable energy maize varieties for Central Europe, (ii) optimal growth periods of energy crops, (iii) the influence of crop management on quality parameters and (iv) environmentally benign crop rotation systems. Differently maturing maize varieties were grown in six different crop rotation systems (continuous maize with and without an undersown grass, maize as a main crop partially preceded by different winter catch crops and followed by winter wheat) and tested at two sites. Additional factors were sowing and/or harvest dates. Maize and cumulative biomass yields of the crop rotation systems were compared. Specific methane yield measurements were carried out to evaluate the energy performance of the tested crops. Quality was assessed either by measurements of the dry matter content or by using the near infrared reflectance spectroscopy for the determination of chemical composition. Results indicate that an environmentally benign crop rotation system requires nearly year-round soil cover to minimize nitrogen leaching. This can be achieved through the cultivation of undersown or catch crops and additional main crops alongside maize, such as winter wheat. Late maturing maize varieties can be cultivated at a site where the maize can build adequate dry matter contents due to a long growth period (late harvest date). The energy generation in terms of methane production was primarily dependent on high biomass yields. It could be further shown that the specific methane yield of maize increased with increasing starch content, digestibility and decreasing fiber content. To conclude, selected site-specific energy crops and crop rotation systems, with suitable crop management, (fertilizer and soil tillage) can produce high quality biomass and the highest net energy return. Lignocellulosic biomass can be optimized for combustion. Wet biomass is an optimal substrate for anaerobic digestion. Profitable energy production is characterized by a high land and energy use efficiency and especially high net energy yields.
Metabolic chamber studies on energy- and macronutrient metabolism : impact of meal skipping and energy flux
(2018) Nas, Alessa; Bosy-Westphal, Anja
The classical concept of body weight regulation attributes the development of obesity to a chronically positive energy balance. There is, however, evidence indicating that beyond this basic concept, the effectiveness of body weight regulation is affected by the circadian regulation of metabolism and the level of energy flux (EF, level of energy balance). Meal skipping affects circadian regulation and might therefore also affect the regulation of body weight. In addition, an asymmetric regulation of body weight is hypothesized with improved effectiveness when EF is high (active lifestyle) and less effectiveness at a low EF (sedentary lifestyle). Metabolic chambers offer the opportunity to acquire short-term parameters of energy and macronutrient balance that precede long-term weight gain and therefore, can help to understand the impact of nutrition and physical activity interventions on body weight regulation. This thesis presents the implementation of a metabolic chamber system (Chapter II) and investigates the acute impact of meal skipping (Chapter III) and energy flux (Chapter IV) on energy and macronutrient metabolism by performing two well-controlled, cross-over intervention studies using metabolic chambers. The implementation of the metabolic chambers revealed, that thorough considerations must be made in terms of the metabolic chamber environment (room ventilation and position of analyzer unit), the additional devices (e.g. air conditioner) used as well as the study protocol, in order to obtain good data quality. The study on meal skipping includes 17 healthy participants who underwent 3 isocaloric 24-h interventions (55%, 30%, and 15% carbohydrate, fat and protein, respectively): a breakfast skipping day (BSD) and a dinner skipping day (DSD) separated by a conventional 3-meal-structure day (control). Energy and macronutrient balance were measured and postprandial glucose and insulin concentrations, as well as 24-h glycemia and 24-h insulin secretion (C-peptide), were analyzed. When compared with the 3-meal control, 24-h energy expenditure was higher on DSD (DSD: +69 kcal/d; p < 0.05), but not on BSD. Whereas, fat oxidation increased on the BSD only (+13 g/d; p < 0.01). Spontaneous physical activity, 24-h glycemia, and 24-h insulin secretion did not differ between intervention days. The postprandial homeostasis model assessment index (+54%) and glucose concentrations after lunch (+46%) were, however, higher on the BSD than on the DSD (both p < 0.05). When compared with 3 meals/d, dinner skipping increased energy expenditure. In contrast, higher postprandial insulin concentrations and increased fat oxidation with breakfast skipping show the development of metabolic inflexibility in response to prolonged fasting that may in the long-term lead to impaired glucose homeostasis. The study on energy flux includes 16 healthy participants who underwent three 24-h interventions with different levels of EF: (i) low EF, physical activity level (PAL) = 1.3 – 1.4 (ii) medium EF, PAL = 1.5 – 1.6 and (iii) high EF, PAL = 1.7 – 1.8 each at energy balance (EB), caloric restriction (CR), and overfeeding (OF) (100%, 75% and 125% of individual energy requirement with 50% carbohydrate, 35% fat, 15% protein). Different levels of EF were accomplished by walking (4 km/h) on a treadmill (0, 165 and 330 min). Sleeping energy expenditure (SEE), 24-h macronutrient oxidation and relative macronutrient balance (oxidation relative to intake) were determined. During EB and OF, 24-h fat oxidation increased with higher EF. This resulted in a higher relative fat balance at medium EF (EB: +17%, OF: +14%) and high EF (EB: +23%, OF: +17%) compared to low EF (all p < 0.05). SEE during EB and OF was higher at medium (EB: +5 kcal/3h and OF: +12 kcal/3h) and high (EB: +7 kcal/3h and OF: +18 kcal/3h) EF compared to low EF (all, p < 0.05). In contrast, during CR 24-h fat oxidation was only higher at high EF compared to low EF and neither relative fat balance nor SEE differed between the EF levels. A higher EF might have beneficial effects on body weight regulation during short-term overfeeding and energy balance because it increased SEE and improved relative fat balance. However, during short-term caloric restriction, a higher EF had no impact on the regulation of energy or fat balance. Therefore, a high EF especially can attenuate the adverse effects of short-term overfeeding. Altogether, this thesis emphasizes the importance of physical activity in daily life and suggests that the adverse metabolic outcome of breakfast skipping (caused by a positive energy balance after lunch with a preceding prolonged fasting period) might be attenuated by a high EF.
Optimierung und Bewertung der Produktion von Getreidekorngut als Rohstoff für die Bioethanolerzeugung
(2001) Rosenberger, Alexander; Aufhammer, Walter
Varied cultivation of high yielding winter cereals to be used as bioethanol grains were examined regarding agronomic and fermentation traits as well as with respect to energetic, economic and environmental aspects. Empirical data were taken from biennial factorial field trials with winter cereals at two different experimental sites of Hohenheim University. These are the central conclusions: A-state-of-the-art conversion process presupposed, the cultivation of high-yielding cereals in crop rotations including previous legume crops is an energetically and economically efficient option to optimize the production of bioethanol grain and hence of bioethanol. From the ecologic view, crop production aligned to high grain yields is conflicting with respect to the enhancement of fossil primary energy conservation and thus the avoidance of greenhouse gas emissions relative to the reference fossil fuel and incremental releases of other ecologically relevant substances as compared to low-input crop management.
The prediction of energy balance of dairy cows from animal, feed, and milk traits with special regard to milk fatty acids
(2017) Becher, Vera; Rodehutscord, Markus
The objective of the present study was to predict the energy balance (EB) of dairy cows from animal, feed, and milk traits. As the milk fatty acid (FA) profile is known to react to physiological conditions like an energy deficit, special regard was given to milk FA in order to identify new potential indicators for negative EB. Visiting six experimental stations in Germany, single milk samples were taken from dairy cows between their 6th and 133th day in milk to create a dataset covering a large spectrum of EB and a variety of practical diets. The milk composition was analyzed by mid-infrared spectrometry, and the milk FA profile via gas chromatography. Energy balance (MJ NEL/d), as response variable, was calculated by subtracting the cow’s energy requirements from energy intake. As candidate variables parity, day of lactation, dietary nutrient composition, milk yield, milk composition, and the milk FA profile were provided resulting in a pool of 62 potential predictors. The prediction of EB was performed in two different ways: first, an automated stepwise variable selection was performed with the whole variable pool (GLMs-N) and with FA only (GLMs-FA-N). As this method recently earned criticism, some other methods were also tested for a first variable selection: the regularized linear regression models Lasso, elastic net (ENET), adaptive Lasso (AdaLasso), and adaptive elastic net (ADAENET). As a machine learning method which also considers interactions and non-linear relationships random forests were also applied. The first variable selection was performed using a five-fold cross-validation which resulted in five models per selection method. All chosen effects were combined to one model (MODEL1) for each method, respectively. Following this, the individual effects of the MODEL1 were used for a forward selection based on the corrected Akaike Information Criterion (AICC) for further model reduction, resulting in MODEL2. Then, the non-significant effects were removed from the MODEL2, achieving the final MODEL3 for each method. The final models were validated using leave-one-out cross-validation. The models showed adequate correlations (r) between the predicted and the observed EB in leave-one-out cross-validation: although GLMs-FA-N had the lowest accuracy (r = 0.79), the result was still remarkable and showed how much information milk FA alone can provide. GLMs-N and AdaLasso performed best with r = 0.86 and 0.85 containing 21 and 18 predictors, respectively. However, other models like ADAENET achieved only slightly lower accuracy (r = 0.83) with only 6 predictors. The composition of the predictors was relatively similar in all models. All (except for GLMs-FA-N) contained days in milk, milk yield, C18:1c9, C15:0iso, and the ratio of omega-6 to omega-3 FA (n-6/n-3) as effects with the strongest impacts on the prediction. While milk yield, days in milk, and C18:1c9 mirrored physiologically obvious effects, the strong and positive impact of n-6/n-3 and C15:0iso was unexpected. The n-6/n-3 ratio might be physiologically connected to EB as might reflect the dietary forage-to-concentrate ratio which influences dietary energy content and thus EB. The importance of C15:0iso, a FA arising from microbial FA synthesis in the rumen, could not be explained satisfyingly. The nature of the potential physiological connections between EB and some FA like C15:0iso or n-6 or n-3 FA might require further research. The present study showed that it is possible to predict the cow’s EB from animal and milk traits with an adequate accuracy. As long as the diets have similar composition and not contain ingredients which strongly affect the milk FA profile, dietary effects have not to be taken into account. However, a practical application of the obtained models is not yet possible: First, as the dataset was relatively small (n = 248), it is not clear whether or not the models would perform adequately with independent datasets. Second, FA analysis by gas chromatography is very expensive. Third, even if gas chromatographic analysis were affordable for standard milk analysis, there are some highly variable, very low concentrated FA as predictors in the models, which might be prone to laboratory effects, and this could spoil the predictions. Although under criticism, automatic stepwise selection provided the best performing model and thus seems sufficient for practical issues like the one dealt with in the present study. However, the differences in accuracy between the applied methods were very small and as regularized linear regression methods, especially ENET and ADAENET, are supposed to deal better with highly correlated variables, it might be safer to use them with datasets containing highly correlated variables such as the one used in the present work.
Towards a better understanding of land surface exchange processes over agricultural crop stands
(2020) Bohm, Kristina; Streck, Thilo
Weather and climate models are useful tools for projecting the influence of global climate change on the regional scale. These models are critically dependent on an accurate representation of soil-plant-atmosphere interactions, which are simulated by Land Surface Models (LSMs). The present PhD thesis was designed to improve the representation of land surface exchange processes of croplands in the Noah-MP land surface model. This thesis aims: a) to elucidate the nature of the energy imbalance over a winter wheat stand and to identify the appropriate post-closure method for the study region Kraichgau, southwest Germany; b) to improve the representation of the green vegetation fraction (GVF) dynamics of croplands in the Noah-MP for a more accurate computation of surface energy and water fluxes; and c) to determine the effect of aggregating different crop types with various shares into a single generic cropland class on the simulation of water and energy exchange between land surface and atmosphere.