Yield Gap Analysis for Tanzania – The Impacts of Climate, Management, and Socio-economic Impacts on Maize Yields

AbstractFood security will be the biggest challenge for Tanzania in the next decades. Besides, Tanzania has a multifarious ecosystem, which is endangered through not adapted agronomic practices. Current innovation strategies focus mostly either on the issue of food security or on environmental damages, but rarely on both issues. However, both issues are very crucial. With crop models, a wide range of agricultural practices can be investigated to show possibilities to optimize the application of these practices. Model assessments allow to separate the effects of agronomic and climatic conditions. The process-based model SWIM (Soil and Water Integrated Model) can compute the impacts of agronomic practices and thus develop strategies to decrease the yield gap between actual (farm) yields (Ya) and potential yields (Yp). The Yp are limited through the nutrient (Yn) and water supply and reduced by pests, diseases, and weeds. Furthermore, socio-economic impacts are also relevant (knowledge, tradition, or culture). These impacts can be captured by statistical crop models. Due to regional-adapted, integrated agronomic practices, Ya can be increased and thus the yield gap between Ya and Yp can be decreased. However, enhanced yields due to sufficient nutrient supply are more sensitive on climate (higher yield volatility). In particular, for innovative farmers increase the production risk of climate change impacts. These endangered adaptation from farmers and therefore both food security and the environment. However, not all influences between Ya and Yn can be explained by agronomic (fertilizer application, harvest time, tillage, and plant protection) and climatic conditions. Additionally, the Ya are affected by a broad range of non- biophysical, socio economic constraints. To decrease the yield gap on regional level, agricultural practices and knowledge are required, which consider regional-specific the issue of food security and environmental protection in a balanced ratio

Study on the influence of weather periods on the occurrence of leaf rust and powdery mildew in winter wheat using an interval-based correlation approach

Braunrost des Weizens (Puccinia triticina) und Echter Mehltau des Weizens (Blumeria graminis f. sp. tritici) gehören zu den wichtigsten Schadorganismen an Win­terweizen in Deutschland. Der Einfluss von Witterungsperioden auf beide Krankheiten ist bisher wenig verstanden. Daten zur Befallsstärke von Braunrost und echtem Mehltau an Winterweizen der Jahre 1976 bis 2010 konnten für verschiedene Standorte in Sachsen-Anhalt analysiert werden. Ein „window pane“ Algorithmus wurde verwendet, um Zusammenhänge zwischen Witterung und Schaderregerauftreten zu analysieren und für beide Schaderreger zu vergleichen. Mit diesem Ansatz war es möglich über 300 000 mögliche Zusammenhänge zwischen klimatischen Parametern und dem Auftreten der agrarischen Schaderreger zu untersuchen. Um tiefer gehende Einblicke in die Zusammenhänge zwischen Witterung und Schaderregerentwicklung und ihre zeitliche Variabilität während der Vegetationszeit zu bekommen, wurden Korrelogramme erstellt. Es wurde der Einfluss von Temperatur, Niederschlagssumme, Globalstrahlung und weiteren Parametern untersucht. Dabei konnten zahlreiche signifikant positive und negative Effekte auf das Auftreten der Pilzkrankheiten belegt werden. Zum Beispiel stand das Auftreten von P. triticina im direkten positiven Zusammenhang mit der mittleren Temperatur im Frühjahr, Winter und Herbst. Das Auftreten von Blumeria graminis f. sp. tritici zeigte einen signifikant negativen Zusammenhang mit der täglichen Anzahl an Sonnenstunden von Jahresbeginn bis zur Blüte. Die Ergebnisse werden mit Literaturangaben verglichen und neue Erkenntnisse diskutiert.    Leaf rust (Puccinia triticina) and powdery mildew (Blumeria graminis f. sp. tritici) are among the most important diseases on winter wheat in Germany. The influence of weather periods on both diseases is little understood. Data on leaf rust and powdery mildew severity from 1976 to 2010 at different sites in the state of Saxony-Anhalt were used in the present study. The “window pane” algorithm was used to analyze and compare the disease-weather relationships for both pathogens. Over 300,000 possible relationships between climate variables and disease occurrence were analyzed using this approach. The results were displayed as correlograms to gain profound insight into disease-weather relationships and their temporal variability during the epidemic year. Our analysis of the influence of temperature, precipitation sums, radiation and further climatic variables on leaf rust and powdery mildew infestation on winter wheat showed numerous significantly positive and negative effects on the occurrence of both diseases. The occurrence of P. triticina showed positive relationships with mean daily temperatures during spring, winter and autumn. There were significant negative correlations between B. graminis occurrence and mean sunshine duration per day from the beginning of the year until anthesis. Finally, our findings are compared to those in the literature, and new perceptions are discussed.   &nbsp

Level normalized modeling approach of yield volatility for winter wheat and silage maize on different scales within Germany

Wetterbedingte Ertragsschwankungen stellen für die Landwirtschaft ein Produktionsrisiko dar. Besonders problematisch sind dabei negative Ertragsanomalien, die sich durch den Klimawandel häufen können. Im Rahmen dieser Studie wurden statistische Ertragsmodelle entwickelt und getestet, mit denen Ertragsanomalien modelliert und fortgeschrieben werden können. Für die Modellierung wurden als winterannuelle Kultur Winterweizen und als sommerannuelle Kultur Silomais als die Kulturen mit dem jeweils größten Anbauumfang in Deutschland ausgewählt. Die Erträge dieser beiden Kulturen wurden auf Landkreisebene modelliert und dann auf der Ebene der Bundesländer, Flusseinzugsgebiete und für Deutschland verglichen. Dazu wurden drei statistische Ansätze verwendet: separate Zeitreihenmodelle, Paneldatenmodelle und Zufallskoeffizientenmodelle. Über die funktionale Form der Cobb-Douglas-Produktionsfunktion wurden relative Änderungen im Vergleich zum Vorjahr (Ertrags- und Faktoranomalien) miteinander in Beziehung gesetzt. Halb- und vierteljährlich summierte Klimavariablen gingen in die Modellbildung ein. Den Klimaeinfluss verzerrende ökonomische Einflüsse wurden von Proxyvariablen quantifiziert. Die Ergebnisse (gemessen am Nash-Sutcliffe Modell-Effizienz-Koeffizienten) der Studie zeigten, dass die methodisch einfachsten separaten Zeitreihenmodelle Ertragsanomalien durchgehend besser (0.81) erklärten als die Paneldatenmodelle (0.72) und auch außergewöhnliche, landkreisindividuelle Ertragsänderungen erfassten. Die Erklärungskraft der Zufallskoeffizientenmodelle lag zwischen den separaten Zeit­reihenmodellen und den Paneldatenmodellen (0.78). Durch die Aggregation der Landkreiserträge zu Fluss­einzugsgebiets- und Bundesländererträgen wurden höhere Erklärungswerte erreicht (+0.14). Dieser Aggrega­tionseffekt war am höchsten beim Paneldatenmodell für Flusseinzugsgebiete (+0.26). Für beide Kulturen werden ähnliche Erklärungswerte erreicht. Die räumliche Verteilung der Modellparameter spiegelte die vorherrschenden Boden- und Klimaeigenschaften Deutschlands in den unterschiedlichen Entwicklungsperioden wieder. Durch die Normierung sind die Erträge einerseits unabhängig vom technologischen Niveau, andererseits können sie ohne Fehlerkorrektur direkt mit simulierten Wetter- und Klimamodellen kombiniert werden. Durch die grobe zeitliche Einteilung der Klimavariablen lassen sich mit den Modellen robuste Projektionen abgeben. Unsere statistischen Modelle erfassten kollinear verlaufende Faktoren der Ertragsbildung, beispielsweise Schädlinge oder das Anpassungsverhalten der Landwirte an sich ändernde klima­tische oder ökonomische Bedingungen. Dadurch konnten sie Praxiserträge besser abbilden als prozessbasierte Modelle. Die geschätzten statistischen Modelle sind geeignet, um Ertragsanomalien für Wetter- und Klimaprojek­tionen fortzuschreiben. Die separaten Zeitreihenmodelle reproduzierten insgesamt am besten die gemessenen Ertragsänderungen. DOI: 10.5073/JfK.2015.06.01, https://doi.org/10.5073/JfK.2015.06.01Weather-related yield volatility is an important production risk for agriculture. Especially, negative yield anomalies could increase through climate change. We develop and investigate statistical crop yield models which can be used to predict crop yield impacts of weather and climate projections. The models are applied to winter wheat and silage maize, which are the most important annual crops as winter and spring crops, respectively, in Germany. The yields of both crops were modelled on county level, but evaluated on federal state, river basin or national level. We use three regression methods: separate time series model, panel data model, and random coefficient model. Within the Cobb-Douglas production function, relative changes (of yield and factor anomalies) are related to each other. To include the conditions of vegetative and generative plant development, we use climate variables summed to quarter- and half-year values. Furthermore, our models are controlled with proxy variables for economic impacts to estimate unbiased climatic parameters. Our study shows that the simple separate time series models explain (measured by the Nash-Sutcliffe model efficiency coefficient) yield anomalies best. They perform generally better (0.81) than the panel data models (0.72) due to a more accurate reproduction of exceptional yield changes at the county level. The random coefficient models performed between the separate time series models and panel data models (0.78). The aggregation of county yields to federal state and river basin yields improves the model accu­racy by + 0.14. The aggregation effect is at highest for the panel data model on river basin scale (+0.26). The models for both crops achieve a similar goodness of fit. The spatial distribution of model parameters reflects the prevailing soil and climate characteristics within Germany relevant for the different plant development periods. Our statistical models capture collinear factors within yield formation. These are, for example, pests and diseases, or the adaptation behaviour of farmers on changing climatic or economic conditions. Due to the normalization, the yield changes are independent of technological levels and can be combined with weather and climate projection without any bias correction. The coarse temporal subdivision of the climatic variables supports robust assessments of climate change pro­jections. To conclude, our models are suitable for the combination of yield assessments with weather and climate projections, because they reproduce yields from out-of-sample years robustly. In general, the separate time series models reproduce best the measured yield changes. DOI: 10.5073/JfK.2015.06.01, https://doi.org/10.5073/JfK.2015.06.0

THERMODYNAMIC ASPECTS OF DESIGNING THE NEW SIEMENS HIGH PRESSURE STEAM TURBINE WITH OVERLOAD VALVE FOR SUPERCRITICAL APPLICATIONS

Abstract Huge coal fueled power plants in the 1000MW el class are requiring high efficient steam turbines which can handle supercritical steam conditions up to 300bar and 600°C. Besides these boundary conditions, the capability for stabilising the grid fluctuations is also one key requirement. Siemens is focussing on this topic by using the so-called overload valve(s), which enhance the maximum amount of main steam mass flow entering the high-pressure turbine by use of additional valve(s). Using this technique, a power increase in the range of up to 20% is theoretically achievable. Siemens PG has collected a lot of positive service experiences throughout the past decades with this technique, and therefore this principle is being well established in the field. The connection between the additional steam mass flow passing through the overload valve and the standard blading path is somewhat downstream from the first stage. These connecting points can be varied (for this current turbine design) -if necessary -between the third and fifth stage after the turbine inlet. From an economic point of view, the approach of extending the power range via overload valves is even better than throttling the whole machine during standard operating condition and opening the valves fully at certain peak load requirements. Historically based, Siemens designs and manufactures reaction stages, 'reaction turbines', which must be thrust compensated via a separate piston to equalize and reduce the overall axial thrust down to a small number. Increasing the main steam temperatures up to the previously mentioned levels makes the internal cooling device of this thrust equilibrium piston a major key point for the whole turbine. No external cooling pipe-work or special materials are required. In • Developing a turbine-internal cooling system for the thrust equilibrium/balancing piston as well as for the inner and outer casing. • Evaluation of staged piston with new internal cooling system adjusted for the impact on heat rate. • Quantification of all related mass flows, temperatures and pressures. • Axial thrust calculation to determine the required diameters of the staged piston. • General remarks concerning efficiency behaviour of hp-turbines with different geometrical designs. Turbine internal bypass cooling A schematic overview of the internal cooling concept is given in Due to this temperature reduction by the cooling steam, the turbine is capable of handling 600°C main steam temperatures and -in principle -pressure levels up to 300bar. As a consequence, the wall-thickness of the outer casing could be reduced significantly, which is a benefit in overall weight (and therefore costs) and start up behaviour. In addition to these advantages, all bolts for the inner casings could be manufactured out of well established material. Without the internal bypass cooling, these bolts must be made out of a special (very expensive) not proven material. Another major advantage could be seen in the low cycle fatigue performance of the inner casing at the overload admission regime. Without the internal bypass cooling system, the inner casing has to withstand high temperature gradients when the overload valve(s) switch(es) on or off. With this cooling principle, temperatures remain almost constant, regardless of the amount of steam admission. In In front of the first hp-drum a low reaction diagonal inlet stage (impulse blade design) is designated to rapidly reduce the high inlet temperatures, typically with a high stage load number. The corresponding stator vanes are being built as one ring, avoiding high leakage losses compared to conventional stator vanes. The guide vanes of the diagonal stage create a swirl in the direction of rotation, which reduces the static temperature for the first rotor (blade-roots). Additionally, the (often) limited axial length of the blading path can be used more effectively; the possible enthalpy drop within the turbine is enlarged. Different techniques handling overload requirements A brief overview of possible concepts and their impact on the heat rate versus different power settings is given in the next figure, Pure throttling of the turbine control valves is a simple technique for supporting frequency control demands from the grid. The turbine operates up to the rated conditions with the control valves throttled. They can be opened quickly if more power is required. The increased electrical output available to the grid is approx. 3s after reduction of the throttling. A 5% reduction in throttling results in an approx. 2.5% increase in electrical output. If the control valve is throttled by 2%, the increased electrical output from opening the valve is approx. 1.2%. Reducing the throttling from 5% to 2% improves the heat requirement due to a reduction in throttling losses. Using this concept, the best heat rat values are obtained during the peak load requirements of the turbine. The valves are fully open at this position without causing any additional throttling losses. A second alternative technique to handle overload requirements is the use of so called 'control stages' in front of the blade path of the high pressure turbine, see Lowest heat rate during sliding pressure mode No further pressure increase in front of the hpturbine required when the extra power is needed Minimal radial forces acting on the shaft compared to the control-stages principle Fewer components required during maintenance Short outage time due to less complexity In conjunction with the internal bypass cooling pipe work, some additional benefits could be outlined: Symmetrical steam mass flow around the inner casing, which reduces the thermal stress and thermal deformation within the turbine, leading to minimal required radial clearances and therefore maximal overall efficiency and best operation behavior 'Preheating' of some major turbine components, which will result in a reduction of the required heat up time Almost constant temperature level in critical turbine sections, independent of the overload admission whether active or not No impact on turbine life time with respect to numbers of overload cycles As already mentioned in the introductory phrase, Siemens PG has collected a lot of positive field experiences throughout the past decades with the overload-technique, starting in the mid 50s. Today, more than 40 high pressure turbines have been delivered using the overload admission principle. The position inside the turbine at which the admission steam is mixed together with the main steam -varies for different turbine types -and depends of the specified amount of extra power. Location of the overload steam admission within the newly designed hp-turbine In this chapter some calculations regarding the connection of the overload steam admission are presented. The later the overload steam admission occurs, the higher the power or mass flow gain is achieved. By bypassing an increasing number of front stages of a turbine through separate overload valves, more and more additional mass flow can be fed into the turbine without increasing the main steam pressure. Presuming that the cooling steam for the staged piston is being extracted one stage before the overload inlet -as shown in On the other hand, 'excessively cold steam' for the piston and for the outer surface of the inner casing is not recommended. The temperature gradient across the inner casing has to stay within certain limits. With the given internal bypass cooling concept it is principally possible to maintain the 'optimum' cooling temperature for the inner and outer casing as well as for the large piston diameter. The next More information concerning the required piston diameter D 2 is given in A sketch of the internal bypass cooling concept for the hpturbine including the major data for the piston and pipe-work is drawn in 5 Copyright © 2006 by ASME Additionally, the heat rate effect of a staged piston versus a standard piston was being evaluated. Significant lower heat rate behaviour was calculated for the staged piston compared to a 'conventional' one. On one hand, the sealing length for the staged piston could be designed longer than the corresponding length of the standard piston because the main steam inlet area could be placed above the small piston diameter, see Further on, the splitting of each axial sealing length on the piston was optimized. The best variant of all possible combinations for l k1 , l k2 and l k3 was chosen for the current design, which leads to the minimal heat-rate value, see To summarize, during the design phase of the new hp-turbine the overall concept was optimised, taken the followingsometimes counteracting parameters -into account: The resulting leakage mass flow throughout all sealing as a function of the pitch, radial clearance between the sealing strips and the metal as well as the radial clearance between metal and metal, length, existing pressure difference and the steam density The required cooling temperature The required piston diameter to balance the axial thrust when changing the position of the internal bypass cooling concept Blading interactions and restrictions of thinkable positions for the internal bypass cooling within the blading path Mechanical demands Design demands Rotor-dynamic criteria Evaluation of different design features for the newly developed turbine having the internal bypass cooling with respect to the heat rate, power output and hp-efficiency Looking at the power output, heat rate and the hp-efficiency of the new hp-turbine, a comparison of different design features for this turbine is quite important. In a sensitivity study the following major points were analyzed and evaluated. With the new cooling device, the outer surface of the inner casing is cooled down to a certain level. Taken this effect into account leads to the fact that the integral-temperature of the inner casing is not that much higher than the shafttemperature, compared to a 'standard' turbine. Therefore, the radial clearances across the piston and across the first hpdrum are reduced. However, the metal to metal clearances are kept constant to comparable turbines -the so called 'cold' radial clearances -at no load conditions. Due to that more homogeneous temperature field within the turbine at operating conditions the radial clearances will then be smaller. Especially, a reduction in the leakage mass flow across the larger piston -at turbine operating conditionsplays quite an important role in the overall heat rate of the whole turbo-set. Without having the internal bypass cooling, the available axial length for the blading path increases because one extraction slot into the turbine blade-path for this purpose becomes obsolete, see A relatively huge impact on the inner efficiency could be found when the connecting point of the internal cooling could be varied in a wide range. For instance, by lowering the pressure before the larger piston diameter of the staged piston, when connecting this position to a point further downstream in the machine, the leakage mass flow across that piston reduces accordingly. A thermodynamic optimum of this connecting point is somewhere in the middle of the machine. But, this comparison is only valid for turbines with a 'free choice' of the connecting point, which doesn't have an overload capability, mechanic criteria or casting restrictions to fulfil. As well, those that definitely don't prohibit the extraction of too 'cold' cooling steam from the expansion line. When connecting the internal cooling far downstream, the turbine costs will rise. The expensive outer casing at the front end, with 10%Chromium content, gets bigger, whereas the cheaper rear end (1%Cr) gets smaller at the same time. Summary: The net effect of the new cooling principle is at the very least, heat rate invariant (conservative comparison/approximation) or slightly better compared to a conventional turbine design. On average, one will 'loose' half a blade-row, but be able to reduce the radial clearances across the piston as well as for the first drum. Impact of the piston cooling steam from the inner casin

Increasing stomatal conductance inresponse to rising atmospheric CO2

Background and Aims: Studies have indicated that plant stomatal conductance (gs) decreases in response to elevated atmospheric CO2, a phenomenon of significance for the global hydrological cycle. However, gs increases across certain CO2 ranges have been predicted by optimisation models. The aim of this work was to demonstrate that under certain environmental condition, gs can increase in response to elevated CO2. Methods: When using (i) an extensive, up-to-date, synthesis of gs responses in FACE experiments, (ii) in situ measurements across four biomes showing dynamic gs responses to a CO2 rise of ~50ppm (characterising the change in this greenhouse gas over the past three decades) and (iii) a photosynthesis-stomatal conductance model, it is demonstrated that gs can in some cases increase in response to increasing atmospheric CO2. Key Results: Field observations are corroborated by an extensive synthesis of gs responses in FACE experiments showing that 11.8% of gs responses under experimentally elevated CO2 are positive. They are further supported by a strong data-model fit (r2=0.607) using a stomatal optimization model applied to the field gs dataset. A parameter space identified in the Farquhar-Ball-Berry photosynthesis-stomatal conductance model confirms field observations of increasing gs under elevated CO2 in hot dry conditions. It was shown that contrary to the general assumption, positive gs responses to elevated CO2, although relatively rare, are a feature of woody taxa adapted to warm, low-humidity conditions, and that this response is also demonstrated in global simulations using the Community Land Model (CLM4). Conclusions: The results contradict the over-simplistic notion that global vegetation always responds with decreasing gs to elevated CO2, a finding that has important implications for predicting future vegetation feedbacks on the hydrological cycle at the regional level.Irish Research CouncilScience Foundation Irelan

Integrated assessment of croplands soil carbon sensitivity to recent and future climate in the Elbe river catchment (central Europe)

Carbon storage in soils is sensitive to changing climatic conditions, potentially increasing C fluxes from soils to the atmosphere. This study provides an assessment of recent climate variability (1951–2000) and potential future (2001–2055) climate change impacts on soil C storage for croplands in the German part of the Elbe River basin. Results indicate that recently (1991–2000) croplands are a net source of carbon (net annual flux of 10.8 g C m-2 year-1 to the atmosphere). The recent temperature trend for the years 1951–2000 (+0.8 K in summer and +1.4 K in winter mean temperature) alone have already caused a significant net flux of 1.8 g C m-2 year-1 to the atmosphere. Future climate change (2001–2055) derived from regionalised meteorological properties driven by the IPCC-SRES A1 scenario results in an increased net C flux of an additional 4 g C m-2 year-1 in comparison to the reference period (1951–2000). Uncertainties attached to C flux results are estimated with a standard error of 6%. Besides climate-induced alteration of net C fluxes, considerable impacts on groundwater recharge (−45.7%), river flow (−43.2%) and crop yield (−11% to −15% as a basin-wide average for different cereals) were obtained. Recent past and expected temperature changes within the Elbe basin predominantly contribute to the increase of net C fluxes to the atmosphere. However, decreased crop growth (crop yields) and decreased expected water availability counteract even higher net C losses as soil C turnover is reduced through less C input (less crop growth) and drier soil conditions (decrease in water availability). Based on this study, present-day and potential future development of net C fluxes, water components and crop yields were quantified. This allows integrated assessment of different ecosystem services (C storage, water availability and crop yield) under climate change in river basins

Global evaluation of a semiempirical model for yield anomalies and application to within-season yield forecasting

International audienc

Assessing Uncertainty of Water Availability in a Central-European River Basin (Elbe) Under Climate Change

The Elbe region is representative of humid to semi-humid landscapes in Central Europe, where water availability during the summer season is the limiting factor for plant growth and crop yields, especially in the loess areas with high crop productivity having annual precipitation lower than 500 mm. This paper summarizes the results of the first phase of the GLOWA (GLObal WAter)-Elbe project and tries to assess the reliability of water supply in the German part of the Elbe river basin for the next 50 years, a time scale relevant for the implementation of water and land use management plans. One focus of the study was developing scenarios which are consistent with climate and land use changes considering possible uncertainties. The concluding result of the study is that nature and communities in parts of Central Europe will have to deal with considerably lower water resources under scenario conditions

Nachhaltige Wasser- und Landnutzung im Guanting Einzugsgebiet (China) unter begrenzten Waserressourcen (GUANTING) - Chinesisch-deutsches Gemeinschaftsprojekt, Teilprojekt 1: Koordination, Szenarien des globalen Wandels, integrative Maßnahmenplanung : Schlussbericht ; Projektlaufzeit: 01.06.2009 - 30.11.2012

[no abstract available