1,933 research outputs found
A global FAOSTAT reference database of cropland nutrient budgets and nutrient use efficiency (1961–2020): nitrogen, phosphorus and potassium
Nutrient budgets help to identify the excess or insufficient use of fertilizers and other nutrient sources in agriculture. They allow for the calculation of indicators, such as the nutrient balance (surplus if positive or deficit if negative) and nutrient use efficiency, that help to monitor agricultural productivity and sustainability across the world. We present a global database of country-level budget estimates for nitrogen (N), phosphorus (P) and potassium (K) on cropland. The database, disseminated in FAOSTAT, is meant to provide a global reference, synthesizing and continuously updating the state of the art on this topic. The database covers 205 countries and territories, as well as regional and global aggregates, for the period from 1961 to 2020. Results highlight the wide range in nutrient use and nutrient use efficiencies across geographic regions, nutrients, and time. The average N balance on global cropland has remained fairly steady at about 50–55 kg ha−1 yr−1 during the past 15 years, despite increasing N inputs. Regional trends, however, show recent average N surpluses that range from a low of about 10 kg N ha−1 yr−1 in Africa to more than 90 kg N ha−1 yr−1 in Asia. Encouragingly, average global cropland N use efficiency decreased from about 59 % in 1961 to a low of 43 % in 1988, but it has risen since then to a level of 55 %. Phosphorus deficits are mainly found in Africa, whereas potassium deficits occur in Africa and the Americas. This study introduces improvements over previous work in relation to the key nutrient coefficients affecting nutrient budgets and nutrient use efficiency estimates, especially with respect to nutrient removal in crop products, manure nutrient content, atmospheric deposition and crop biological N fixation rates. We conclude by discussing future research directions and highlighting the need to align statistical definitions across research groups as well as to further refine plant and livestock coefficients and expand estimates to all agricultural land, including nutrient flows in meadows and pastures. Further information is available from https://doi.org/10.5061/dryad.hx3ffbgkh (Ludemann et al., 2023b) as well as the FAOSTAT database (https://www.fao.org/faostat/en/#data/ESB; FAO, 2022a) and is updated annually.</p
Asymmetric Sovereign Risk: Implications for Climate Change Preparation
Sovereign risk exhibits significantly asymmetric reactions to its determinants across the conditional distribution of credit spreads. This aspect, previously overlooked in the literature, carries relevant policy implications. Countries with elevated risk levels are disproportionately affected by climate change vulnerability compared to their lower-risk counterparts, especially in the short term. Factors such as inflation, natural resource rents, and the debt-to-GDP ratio exert different effects between low and high-risk spreads as well. Real growth and terms of trade have a stable but modest impact across the spread distribution. Notably, investing in climate change preparedness proves effective in mitigating vulnerability to climate change, in terms of sovereign risk, particularly for countries with low spreads and long-term debt (advanced economies), where readiness and vulnerability tend to counterbalance each other. However, for countries with high spreads and short-term debt, additional measures are essential as climate change readiness alone is insufficient to offset vulnerability effects in this case. Results also demonstrate that the actual occurrence of natural disasters is less influential than vulnerability to climate change in determining spreads
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Methane Production by Methanogens In Simulated Subsurface Martian Environments
Methane has a typical atmospheric photochemical lifetime of ∼300 years on Mars, making contemporary reported detections (and non-detections) of methane a fiercely debated topic, due to the potential need for a present-day source. On Earth, most methane is produced by methanogenic microbes present in, e.g., ruminants, wetlands, lakes and permafrost. Of the four metabolic pathways on Earth, the hydrogenotrophic pathway is the most common, utilising CO2 and H2 as substrates. Both gases are present on Mars, plus liquid water and essential elements (CHNOPS) that are requirements for life, and organics. Surface conditions on Mars are sterilising, however, the temperature and pressure of the subsurface are potentially favourable to life and provide a shield to sterilising surface conditions, and are thus a possible habitat for methanogens. A meta-analysis was
conducted, motivated by these subsurface parameters, that redefined the statistical representation for several growth parameters for all type-strains of methanogens and analysed multiple parameters
simultaneously across multiple categories (e.g. metabolism), showing that the optimal average conditions in which to grow methanogens would be a meso-temperate (20 to 39◦C), hypersaline and slightly acidic environment. Two martian subsurface environments were simulated to determine whether environmental or chemical factors are inhibitory to methanogenesis. (1) Methanoculleus marisnigri was grown in a custom-built, high-pressure manifold at 60 bar and 25◦C to simulate the subsurface of Mars, although no methane was produced, due to a technical issue resulting in oxygenated medium. However, some cells survived five weeks of oxygenation. (2) Methanothermococcus okinawensis was grown in a simulated chemical environment at 1 bar and 60◦C, that included a regolith simulant, a proposed martian brine and a Mars-relevant organic source (carbonaceous chondrite). The simulated parameters of the chemical environment of subsurface Mars were not inhibitory to hydrogenotrophic methanogenesis, suggesting it is feasible (from a metabolic perspective) that subsurface methanogens could be producing contemporary methane on Mars
A First Course in Causal Inference
I developed the lecture notes based on my ``Causal Inference'' course at the
University of California Berkeley over the past seven years. Since half of the
students were undergraduates, my lecture notes only require basic knowledge of
probability theory, statistical inference, and linear and logistic regressions
Analytical validation of innovative magneto-inertial outcomes: a controlled environment study.
peer reviewe
Endozoochorní šíření rostlin volně žijícími herbivory
Endozoochorní disperze semen je velmi častý fenomén, který můžeme pozorovat kdekoli, kde se zvířata živí rostlinami, které nesou zralá semena. Endozoochorie byla popsána jako potenciální mechanismus pro migraci na dlouhou vzdálenost, nicméně je zde velký rozdíl mezi endozoochorií frugivorními zvířaty a herbivory. Navzdory tomu, že herbivorní endozoochorie je známa již více než století, naše znalost tohoto fenoménu je stále omezena, o to více v případě volně žijících, divokých druhů herbivorů. Mimoto se ukazují velké rozdíly v endozoochorní disperzi mezi studovanými oblastmi i mezi studovanými herbivory. To naznačuje, že potřebujeme detailní znalost procesu z různých oblastí, abychom mohli dojít k jakýmkoli závěrům. Předkládaná práce si dala za cíl: (i) popsat druhové složení nalezené v trusu divokých prasat a jelenů, (ii) kvantifikovat efekt jeleního trusu na vegetaci suchých trávníků, (iii) změřit míru adaptace na průchod trávicím traktem u vybraných druhů rostlin, a (iv) rozplést jednotlivé mechanismy ovlivňující druhové složení šířené v trusu. Výsledky mého výzkumu naznačují: (i) druhové složení v trusu se do určité míry liší mezi jeleny a divokými prasaty: některé druhy jsou šířené oběma zvířaty, některé jen jedním z nich. (ii) Depozice jeleního trusu má zanedbatelný efekt na vegetaci suchých...Endozoochorous dispersal of seeds is a very common phenomenon which may occur anywhere some animals feed on plants bearing mature seeds. Endozoochory has been identified as a potential driver for long-distance migration but there is a strong discrepancy between endozoochory by frugivorous animals and herbivores. Despite the fact that the latter has been observed as early as a century ago, our understanding of the herbivorous endozoochory is still limited, even more so when it comes to the free-ranging wild species of herbivores. Furthermore, the endozoochorous dispersal shows significant differences between study areas and between herbivore species suggesting we need information about the process from various study areas to draw any conclusions. This thesis aimed to: (i) research the species composition found in dung samples of wild boars and deer, (ii) quantify the effect of deer dung deposition on vegetation of dry grasslands, (iii) establish the adaptation of plant species to the passage through digestive tract, and (iv) disentangle the drivers of species composition dispersed in dung. The results of my research indicates: (i) the species composition in dung samples differs up to a point between deer and wild boars: some species are dispersed by both dispersers while other only by one of them....Katedra botanikyDepartment of BotanyPřírodovědecká fakultaFaculty of Scienc
Semi-parametric mixtures of quantile regressions
Mini Dissertation (MSc (Advanced Data Analytics))--University of Pretoria, 2023.Mixtures of quantile regressions are explored through the lens of a kernel density
based EM-type algorithm and a newly proposed CEM-type algorithm. This allows the simultaneous clustering and modeling of conditional quantiles without the need to assume symmetric or identical error distributions for any of the components. We conduct simulation studies and apply both algorithms to real life datasets. The first has already been investigated by fitting the EM-type algorithm and we show that the CEM-type algorithm produces similar results. The second is a homoscedastic dataset which has been explored through the lens of univariate quantile regression. We begin by modeling the mixtures of the conditional medians as a robust alternative to mixtures of conditional means. Mixtures of other conditional quantiles are modeled as well to get a more complete understanding of the conditional distribution. This, however, proves to be a challenging task for datasets which are not easily separable and may lead to unsatisfactory results, especially when considering low quantiles or high quantiles such as 0.1 or 0.9 respectively. The theory of the EM-type algorithm is provided in detail and the proposed CEM-type algorithm is shown to provide a substantial improvement in the model convergence speed, but often at the cost of increased bias in the parameter estimates. We conclude with a discussion of some of the limitations and areas for future research.StatisticsMSc (Advanced Data Analytics)Unrestricte
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