Browsing by Subject "Growth"

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Effects of water management on microclimate and yield physiology in irrigated rice in semi-arid environments
(2014) Stürz, Sabine; Asch, Folkard
Growth and grain yield reductions have been widely observed when traditionally flooded rice fields were subjected to water-saving irrigation measures, where a continuous floodwater layer is avoided. These observations led to the perception of rice being a plant extremely sensitive to soil water deficits even when grown in soils close to their water holding capacity. Since the rice plant’s meristem is below the water surface until the early reproductive stage in flooded fields, the difference in heat capacity between water and air can lead to changes in meristem temperature, when a ponded water layer is omitted. Therefore, the objectives of this study were to quantify the effects of water-saving irrigation on the field’s microclimate and its influence on gas-exchange parameters and to investigate growth and yield parameters under flooded and non-flooded conditions in response to microclimate and varying climatic conditions. On two sites in Senegal, field experiments were conducted, where rice was sown on bi-monthly staggered dates and grown under flooded and non-flooded conditions. In the flooded treatment, a ponded water layer was maintained in the field throughout the growing season, whereas in the non-flooded treatment, irrigation water was applied until soil saturation on a frequent basis, in order to avoid standing water and soil water deficits at the same time. Microclimatic parameters and phenology were observed and leaf gas-exchange and plant growth parameters, yield and yield components were determined. Minimum soil temperature and temperature at meristem level were usually lower without standing water, whereupon temperature differences between irrigation treatments increased with decreasing air temperature. Stomatal conductance depended mainly on minimum soil and meristem temperature and minimum relative humidity inside the canopy. Assimilation rate was positively correlated with solar radiation and soil and meristem temperature, but depended mainly on stomatal conductance. Without standing water, stomatal conductance and assimilation rate were significantly lower, but the results could be explained with differences in microclimate. In most cases, leaf area was reduced under non-flooded conditions. Leaf area expansion rate was correlated with meristem temperature during the night. With minimum meristem temperature being lower under non-flooded conditions, lower leaf area expansion rates under non-flooded conditions could be attributed to lower meristem temperature. Yield reductions under non-flooded conditions were mainly observed in the cold-dry-season, whereas slight yield increases were found in the hot-wet-season. Among the yield components, reduced number of spikelets per panicle and decreased spikelet fertility accounted for the largest share of the yield gap. Leaf area per tiller was positively correlated with meristem temperature in the observed temperature range, and a positive relationship was found between leaf area per tiller and the number of spikelets per panicle. Furthermore, spikelet fertility increased with meristem temperature between panicle initiation and booting stage. Therefore, lower meristem temperature led to smaller leaf area per tiller, less spikelets per panicle and decreased spikelet fertility under non-flooded conditions. We concluded that water-saving irrigation in lowland rice production can lead to growth and yield reductions in comparison to traditional lowland irrigation even in the absence of soil water deficits, due to changes in soil and meristem temperature when a ponded water layer is omitted. Differences in assimilation rate, leaf growth and yield between irrigation treatments increased with decreasing air temperature and a clear seasonal pattern was observed, with large growth and yield reductions in the cold-dry-season, whereas in the hot-wet-season, growth and yield were less affected by irrigation treatment. When water-saving irrigation measures are applied in areas where night temperatures below 20°C occur, the effect of changes in meristem temperature should be considered. To mitigate impairment of growth under water-saving irrigation, a floodwater layer could be used to bridge cool periods, or a less temperature-responsive variety should be chosen. Nevertheless, the physiological mechanisms of the differential effects of day and night temperature remain unknown und need further investigation. Possibly, there is a combined effect of low night temperature and high evaporative demand during the day, which could lead to growth limitations due to restrictions of the plant’s water status. Furthermore, we want to highlight the need for a robust model of water temperature in paddy fields, which should be incorporated in rice growth models, since even tough existing models simulate growth and grain yield under upland and lowland conditions, the effects of changes in microclimate due to irrigation method are inadequately considered so far.
Impact of climate change on future barley (Hordeum vulgare L.) production in Ethiopia
(2022) Gardi, Mekides W.; Graeff-Hönninger, Simone
Summary Barley (Hordeum vulgare L.) is the fourth major cereal crop in the world, and it accounts for 8% of the total cereal production in Ethiopia based on cultivation location. Farmers may face unpredictable rainfall and drought stress patterns, such as terminal drought, in which rainfall ends before crops reach physiological maturity, posing a challenge to crop production. Furthermore, climate change is expected to reduce crop production/yield due to increases in carbon dioxide (CO2) and ozone (O3) concentrations, temperatures, and extreme climate events such as floods, storms, and heatwaves, highlighting the importance of taking action to develop climate-resilient cultivars and secure future crop production. Against this background, a meta-analysis study was conducted to synthesize and summarize to assess the overall effect of elevated CO2 (eCO2), and its interaction with nitrogen (N) and temperature on barley grain yield and yield components. A climate chamber experiment was carried out to identify the impacts of projected CO2 enrichment (eCO2) on a set of landraces and released cultivars of Ethiopian barley. The crop-climate modeling approach was used to simulate future climate change and to identify the impacts of climate change on selected barley genotypes and study locations in Ethiopia. Furthermore, adaption options were simulated and identified. Publication I, aimed to answer how eCO2 and its interaction with N and temperature affects barley yield at a global level. Peer-reviewed primary literature (published between 1991-2020) focusing on barley yield responses to eCO2, temperature, and N were searched on different search engines. The response of five yield variables of barley was synthesized and summarized using a meta-analysis technique. Different experimental factors which might affect the estimation of the response of barley yield to eCO2 were calculated. The results revealed that eCO2 increased barley yield components such as vegetative biomass (23.8%), grain number (24.8%), and grain yield (27.4%) at a global level. Barley vegetative biomass and grain yield were increased under the combination of eCO2 with the higher N level (151-200 kg ha-1) compared to the lower levels. Grain number and grain yield were increased when eCO2 combined with temperature level (21-25°C) this response was not evident. The response of barley to eCO2 was different among genotypes and experimental conditions. Publication II, the genetic diversity of Ethiopian barley was screened under eCO2 enrichment in a controlled exposure experiment. The experiment was conducted at the Institute of Landscape and Plant Ecology, the University of Hohenheim in 2019. A total of 30 (15 landrace and 15 released cultivars) were grown under two levels of CO2 concentration (400 and 550 ppm) in climate chambers. Plant-development-related measurements and water consumption were recorded once a week and yield was measured at the final harvest. A significant increment in plant height by 9.5 and 6.7%, vegetative biomass by 7.6 and 9.4%, and grain yield by 34.1 and 40.6% in landraces and released cultivars, respectively were observed due to eCO2. The effect of eCO2 was genotype-dependent, for instance, the response of grain yield in landraces ranged from -25% to +122%, while it was between -42% to 140% in released cultivars. The water-use efficiency of vegetative biomass and grain yield significantly increased by 7.9 and 33.3% in landraces, with 9.5 and 42.9% improvement in released cultivars, respectively under eCO2. Comparing the average response of landraces versus released Ethiopian barley cultivars, the highest percentage yield change due to eCO2 was recorded for released cultivars. However, higher actual yields under both levels of CO2 were observed for landraces. Publication III, Current and future climate change, its impact on Ethiopian barley production, and adaptation options were simulated using the DSSAT-CERES-Barley model. Climate change scenarios were set up over 60 years using Representative Concentration Pathways (4.5 and 8.5), and five Global Climate Models. The changes in Ethiopian climate and barley production were calculated from the baseline period (1981-2010). Different sowing dates, sowing densities, and fertilizer levels were tested as climate change impact mitigation strategies in a sensitivity analysis. The analysis of a crop-climate model revealed an increasing trend of temperature (1.5 to 4.9 °C) and a mixed trend of rainfall (-61.4 to +86.1%) in the barley-producing locations of Ethiopia. The response of two Ethiopian barley cultivars was simulated under different climate change scenarios and a reduction of yield up to 98% was recorded for cv. Traveler while cv. EH-1493 exhibited a reduction of up to 63%. Even though a similar trend was observed for most of the studied locations, cv. EH-1493 showed a yield gain of up to 14.7% at Holeta. The sensitivity analysis on potential adaptation options indicated that the negative effects of climate change could be mitigated by earlier sowing dates, with a 25% higher sowing density and a 50% higher fertilizer rate than the current recommendation. The results of the present dissertation show the change in the Ethiopian climate and its impact on barley production. Barley production could benefit from eCO2; however, the response varied among genotypes, additional stress, and experimental condition. A reduction of barley grain yield under different climate change scenarios was observed mainly due to increasing temperature. However, the reduction could be minimized through different adaptation options. The information from the current dissertation could be used to identify agro-economic implications of CO2 enrichment and climate variability on yield regarding appropriate genotype selection and adaptation of regional cropping systems (e.g., management and breeding strategies). Further experimental studies assessing crop production, nutritional quality, and adaptation options under multifactor climate conditions should be carried out to increase basic understanding and identify genotypes for future breeding programs.
Seasonal variation in growth, quantitative and qualitative food consumption of milkfish, Chanos chanos (Forsskål 1775), and Nile tilapia, Oreochromis niloticus (L. 1758), in Laguna de Bay, Philippines
(2002) Richter, Hartmut; Becker, Klaus
Laguna de Bay, the largest lake in the Philippines, lies directly southeast of the capital Manila. The lake has a mean depth of only 2.8m and a muddy bottom which is stirred during windy weather, causing turbid conditions (Secchi depth <30cm). In the dry season, the water level drops below that of the nearby sea, leading to a backflow of saline water which clears the water until the return of the monsoon winds (Secchi depth >100cm) and leads to algal blooms. Since the beginning of the 1970s, the lake has been used for culturing milkfish, Chanos chanos (Forsskål), in large netpens (max. 2000ha) and Nile tilapia, Oreochromis niloticus (L.), in smaller cages (max. 200m2). Initially, it was possible during the algal blooms to grow fish from fingerling (ca. 10g) to marketable size (ca. 200g) in three months, making two harvests a year possible. Aquaculture quickly spread until in the middle of the eighties, over a third of the lake was covered with cages. At the same time the growth of the fish declined, which was attributed to the excessive use of primary production. Since then, despite a reduction in aquaculture coverage to the generally recommended level of 10% of the lake, fish growth has never reached the levels of the early days of culture. In the present work, seasonal variation in growth, feeding spectrum and daily ration of these two species was to be investigated in relation to water quality in order to find out more about the interaction between aquaculture and the lake. Between May 1995 and August 1997, milkfish and tilapia were sampled on several occasions at commercial operations over the 24-hour cycle. Since milkfish, unlike tilapia, do not receive supplemental feed, the proportion of their growth derived only from natural food could be determined from the cultured fish. Tilapia were kept in cages without feed specially for this purpose and measured and weighed twice a month between March and November 1997. At the same time, selective water quality parameters (particulate organic and inorganic matter, Chlorophyll-a, zooplankton) were analysed weekly. The growth of unfed fish was significantly faster between saltwater intrusion (mid-May) and the return of the monsoons (late July) than at other times of the year. On the other hand, food consumption was only slightly higher in tilapia when the water was clear than at other times and in milkfish hardly differed over the year. Both species mainly fed on amorphous organic detritus; significant levels of phytoplankton were only found in the stomachs at times of algal bloom. In supplemented tilapia, the daily ration still consisted of 35-75% natural food, suggesting that pelleted feed was used inefficiently. The main factor limiting fish growth therefore seemed to be food quality since detritus has often been shown to be poor quality food. The weekly water samples collected in 1997 demonstrated that the total level of phytoplankton was not necessarily higher at times of rapid fish growth. The main difference was related to algal size, since at times of turbid water, small diatoms dominated but these were replaced by larger blue-green algae after saltwater intrusion. In conjunction with the feeding method of these fish, the strongly seasonal growth of the fish could now be explained. Phytoplanktivorous fish such as milkfish and tilapia can only select their food on the basis of size. Since the organic detritus in the lake consisted of particles smaller than 15µm, it was possible for the fish to selectively filter larger blue-green algae but not smaller diatoms. This could also explain why fish growth rates did not recover after a reduction in aquaculture in the mid-eighties, since the relationship between the level of algae and that of detritus seems to be more important than total algal biomass. In order to increase production to those levels found in the early seventies, the level of detritus in the lake would have to be reduced, for which its origin would have to be investigated first.
Three essays in empirical economics
(2019) Seiffert, Sebastian Daniel; Beißinger, Thomas
In the preface of one of the most established textbooks "Economics" by Samuelson and Nordhaus (1998), the authors state that the ultimate goal of economics is to improve the living conditions of people in their everyday life". In this spirit, the underlying thesis empirically assesses three heterogenous topics which all can be linked via their impact on (economic) well-being. It contributes to the scientific landscape by tackling the questions at hand utilising novel and newly constructed data sets which have not been commonly used in economic research. The thesis comprises three chapters which will be summarised in the following. Gun Violence in the US: Correlates and Causes This chapter provides a county-level investigation of the economically-motivated gun violence in the US. To guide our empirical analysis, we develop a simple theoretical model which suggests that firearm-related robberies in a given county increase with the number of illegal guns and decrease with social capital and police intensity. Using detailed FBI data from 1986-2014, we find empirical evidence for the role of illegal guns, social capital, and police intensity in line with our theoretical predictions. To investigate the causal effect of illegal guns, we exploit plausibly exogenous variation in illegal firearm supplies due to gun thefts in contiguous states. The Size of the Middle Class and Educational Outcomes: Theory and Evidence from the Indian Subcontinent This chapter proposes a stylised model to derive the effect of a sizeable middle class on average educational outcomes. Under the reasonable assumptions, the model predicts that the spending share on education increases if the middle class becomes larger such that the size of the middle class has a positive impact on education. We test the relationship empirically by using village/neighbourhood level data from Indian household surveys. To tackle the the issue of potential endogeneity of the middle class share of the population, we propose a novel instrument that relies on the fraction of the population belonging to the third (middle) caste ("sudra"). Using this IV strategy, our empirical results support a positive effect. Go East: On the Impact of the Transsiberian Railway on Economic Development in Eastern Russia This chapter addresses the question whether or not large-scale infrastructure investments have a causal effect of local economic development. By using a novel instrumental variable approach based on historical trade and travel routes across the Russian East, I am able to identify a causal and negative effect of remoteness to the Transsiberian Railway on local economic activity as measured by nocturnal lights emission.
Three pillars of urbanization : migration, aging, and growth
(2018) Südekum, Jens; Prettner, Klaus; Grafeneder-Weissteiner, Theresa
Economic development in industrialized countries is characterized by rising per capita GDP, increasing life expectancy, and an ever larger share of the population living in cities. We explain this pattern within a regional innovation-driven economic growth model with labor mobility and a demographic structure of overlapping generations. The model shows that there is a natural tendency for core-periphery structures to emerge in modern knowledge-based economies.