1,721,009 research outputs found
Temporal dynamics of sugar beet (Beta vulgaris L.) N supply from cover crops differing in biomass quantity and composition
Full text linkCover crops are supposed to decrease the soil mineral N content (N(min)) during winter and increase the N supply to subsequent main crops due to mineralization of N previously prevented from leaching. However, data on N supply from cover crops grown before sugar beet have rarely been reported for Central European conditions. Therefore, our study aimed to provide information for cover crops differing in frost resistance and biomass quantity applicable for N fertilizer dressing in the subsequent main crop. In 2018/19 and 2019/20, field trials were conducted on two Luvisol sites in Germany typical for sugar beet cultivation, comprising a sequence of autumn sown cover crops grown after field pea followed by unfertilized sugar beet main crops sown in next spring. Apparent net N mineralization and the N effect of cover crops on sugar beet were calculated according to a mass balance approach including N(min) and sugar beet N uptake. Winter rye and oil radish revealed the greatest potential for scavenging nitrate from the soil profile while reductions caused by frost-sensitive saia oat and spring vetch were more variable. The amount of N in the cover crop biomass was negatively correlated with N(min) in autumn and also in spring. Thus, for environmentally effective cover cropping in Central Europe, species with a sufficiently high frost tolerance should be chosen. Despite cover crop N uptake up to 170 kg N ha(−1) and C:N ratios < 20, a positive N effect on sugar beet was only found between March and July of the beet growing season and was 50 kg N ha(−1) at maximum, while between August and September, net immobilization was predominant with up to 100 kg N ha(−1). Differences among crop species were not consistent across the site/years investigated. Sugar yield was lowest after rye at 3 sites/years and correlated positively with N(min) in spring. Correlation between yield and cover crop N effect was mostly low and inconsistent and could not be improved by a multiple regression approach. Thus, factors other than in-season N supply from cover crops apparently impacted sugar beet yield formation to a larger extent
Regulation of winter soil mineral nitrogen and N2O emissions by cover crop termination timing
Full text linkAbstract Cover crops (CCs) are widely promoted for reducing nitrate leaching and enhancing soil fertility, yet their role in regulating winter nitrous oxide (N 2 O) emissions remains poorly understood. This field study assessed how termination timing of oil radish ( Raphanus sativus ) influenced soil mineral nitrogen (SMN) dynamics and winter N 2 O emissions across five site-years in a humid temperate climate (Germany) on contrasting soil textures (loamy and sandy). Treatments included autumn termination, spring termination, and fallow. Although CCs reduced SMN by ~ 65% compared to fallow by December, this did not lead to lower winter N 2 O emissions. Instead, cumulative emissions over a standardized 100-day winter period were highest under autumn termination (1.23 ± 0.11 kg N 2 O–N ha −1 ), followed by spring termination (0.65 ± 0.06 kg N 2 O–N ha −1 ) and fallow (0.12 ± 0.01 kg N 2 O–N ha −1 ). Emissions were higher in 2019 than 2020, associated with warmer and wetter conditions. Autumn termination also increased spring SMN levels relative to spring termination in loamy soils, but not in sandy soils, where nitrate leaching may have occurred. While microbial gene abundances indicated greater nitrification and denitrification potential under autumn termination, they did not correlate with actual N 2 O fluxes. These findings suggest that autumn termination can enhance winter emissions, whereas delayed termination may shift emissions to spring, particularly under fertilized conditions. Site-specific CC management that considers termination timing, soil texture, and climatic context is essential to balance nitrogen retention with N 2 O mitigation.Bundesministerium für Ernährung und Landwirtschaft https://doi.org/10.13039/501100005908Georg-August-Universität Göttingen 50110000338
Absorption of¹⁵N enriched ammonia by winter wheat at different growth stages
No full textBackgroundLoss of gaseous reactive nitrogen in the form of aerosols may impact human health, and its deposition leads to eutrophication and acidification of natural ecosystems. In order to reduce ammonia (NH3) emissions, which are a main pathway of nitrogen loss to the environment, accurate monitoring and understanding of the factors involved is required.AimsAs information on the absorption of NH3 by wheat plants in central Europe is scarce, we conducted a field experiment to quantify NH3 absorption by a winter wheat canopy in May and June with each two emission scenarios (5 and 12 kg NH3‐N ha−1).MethodsTo induce NH3 emissions, a 15N enriched ammonium sulfate solution (pH 9) was applied in trays between the wheat rows.ResultsAbsorption of the volatilized NH3 of the aboveground plant biomass ranged between 23 and 181 mg NH3‐N m−2 (corresponding to 14.8% and 20.0% of the emitted NH3) and was significantly higher during the first sampling in May, when compared to the second sampling in June. A higher emission led to a higher absolute amount absorbed.ConclusionsThe results indicate that wheat will indeed absorb significant amounts of NH3 emitted at ground level. They will be useful for further improving NH3 emission factors and the understanding of the NH3 emission pathway.Landwirtschaftliche Rentenbank http://dx.doi.org/10.13039/50110001868
Evaluating N 2 O emissions and carbon sequestration in temperate croplands with cover crops: insights from field trials
Full text linkAbstract. Cover crops (CCs) are acclaimed for enhancing the environmental sustainability of agricultural practices by aiding in carbon (C) sequestration and reducing losses of soil mineral nitrogen (SMN) after harvest. Yet, their influence on nitrous oxide (N2O) emissions – a potent greenhouse gas – presents a complex challenge, with findings varying across different studies. This research aimed to elucidate the effects of various winter CCs – winter rye (frost-tolerant grass), saia oat (frost-sensitive grass), and spring vetch (frost-sensitive legume) – compared to a bare fallow control on SMN dynamics, N2O emissions, and C sequestration. These effects were determined by measuring SMN dynamics and N2O emissions in field experiments. The effects of CCs on soil C sequestration over a 50-year period were predicted by soil organic C (SOC) models using measured aboveground and belowground CC biomass. While CCs efficiently lowered SMN levels during their growth, they slightly increased N2O emissions compared to bare fallow. In particular, winter frost events triggered significant emissions from the frost-sensitive varieties. Moreover, residue incorporation and tillage practices were associated with increased N2O emissions in all CC treatments. Winter rye, characterized by its high biomass production and nitrogen (N) uptake, was associated with the highest cumulative N2O emissions, highlighting the influence of biomass management and tillage practices on N cycling and N2O emissions. The CC treatment resulted in a slight increase in direct N2O emissions (4.5±3.0, 2.7±1.4, and 3.1±3.8kgN2O-Nha-1 for rye, oat, and vetch, respectively) compared to the fallow (2.6±1.7kgN2O-Nha-1) over the entire trial period (18 months). However, the potential of non-legume CCs to reduce indirect N2O emissions compared to fallow (0.3±0.4 and 0.2±0.1kgN2O-Nha-1a-1 for rye and oat, respectively) and their contribution to C sequestration (120–150 kgCha-1a-1 over a period of 50 years when CCs were grown every fourth year) might partially counterbalance these emissions. Thus, while CCs provide environmental benefits, their net impact on N2O emissions requires further research into optimized CC selection and management strategies tailored to specific site conditions to fully exploit their environmental advantages
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Correction to: Nitrification inhibitors reduce N2O emissions induced by application of biogas digestate to oilseed rape
No full textFreisetzung und Verbrauch der klimarelevanten Spurengase N 2 O und CH 4 eines landwirtschaftlich genutzten Bodens in Abhängigkeit von Kultur und N-Düngung, unter besonderer Berücksichtigung des Kartoffelbaus
No full textVariations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Freisetzung und Verbrauch der klimarelevanten Spurengase N 2 O und CH 4 eines landwirtschaftlich genutzten Bodens in Abhängigkeit von Kultur und N-Düngung, unter besonderer Berücksichtigung des Kartoffelbaus
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