1,721,215 research outputs found
Multi-objective optimisation of a model of the decomposition of animal slurry in soil : Tradeoffs between simulated C and N dynamics
No full textTo formulate best management practices for animal slurry, it is important to understand and predict its decomposition in the soil. Slurry decomposition dynamics can be studied by measuring CO2 fluxes and soil mineral nitrogen concentration during laboratory incubations and subsequently calibrating a simulation model. Carbon and nitrogen dynamics are linked and both should be properly simulated. In this work we wanted to identify the tradeoffs between errors in the simulation of C respiration and of soil inorganic N concentration.
We optimised six parameters of CN-SIM (a mechanistic dynamic simulation model), using data of respired C and soil inorganic N measured during a 180-day laboratory incubation of five dairy slurries on three soils. Optimisation was carried out with a multi-objective genetic algorithm (NSGA-II), by minimising the Relative Root Mean Squared Error (RRMSE) between observations and simulations.
The simulation of C respiration was frequently conflicting with the simulation of inorganic N, i.e. low RRMSE–CO2 corresponded with high RRMSE–N and vice versa. When minimising RRMSE–CO2 a set of parameters was obtained that enhanced microbial N immobilisation and reduced the turnover of the organic pools, to match the observed decrease of inorganic N in the 28 days after slurry addition to soil. Remineralisation occurring in the following 150 days caused a marked overestimation of inorganic N. When minimising RRMSE–N, the optimisation provided parameters that strongly reduced remineralisation of immobilised N by markedly diminishing C respiration, with a consequent underestimation of CO2 emission. A modified version of the model, containing a simple implementation of denitrification and of clay fixation/release of ammonium, performed better than the original model for most treatments.
We conclude that the mineralisation/immobilisation turnover in the model is not fully adequate to represent C and N dynamics. We also discuss the implementation of changes (time-varying microbial efficiency and C to N ratio; simulation of ammonium clay fixation and emissions of N2/N2O) to improve model performance
CARBON AND NITROGEN DYNAMICS IN SOILS AFTER REPEATED MANURE APPLICATIONS: MEASUREMENTS AND MECHANISTIC SIMULATIONS.
No full textThe first part of this Ph. D. Thesis (Chapters 1 and 2) is relative to the calibration of a soil organic matter simulation model (the CN-SIM model) by applying it to an experimental data-set, using two different methodologies, in order to verify its conceptual structure and obtaining parameters to describe the partitioning of C and N within the manures. Based on the optimization results, it emerged that the low model performance could be attributed to the lack of some processes involving mineral nitrogen transformations into the soil. In order to better understand the nitrogen dynamics following manure application to the soil, an incubation experiment was build up. In the experiment, two different manures were applied to two soils of different texture, and, in order to estimate the contribution of manure recalcitrant fractions to the mineralization dynamics of C and N in the soil (residual effect of added manure carbon and nitrogen), each manure was applied four times on the same soil (Chapter 3). In the incubation experiment were included measurements of non-exchangeable ammonium, with the aim of better understand if the lower recoveries of added manure ammonium, often found on the clay soils, were due to microbial biomass immobilization or ammonium clay-fixation. Measurements obtained in the incubation experiment were the used to perform a preliminary modification of the CN-SIM model to take into account the ammonium fixation and release processes (Charter 4)
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
Measuring and modeling soil carbon respiration following repeated dairy slurry application
No full textFarm animal manure slurries are repeatedly applied to soils. The portion of slurry organic matter not decomposed within its application year is left to mineralize over subsequent years, which results in a residual effect of high C mineralization in historically-amended vs. nonamended soils. This process was modeled in laboratory incubation by applying water, ammonium sulfate, heifer (HEI), or dairy cow (COW) slurry between 1 and 4 times (at Day 0, 84, 168, and 252) to soils of contrasting textures [sandy-loam (SL) and clayloam (CL)]. Respired CO2 was measured 6 to 10 times after each application along the trial period. Results showed daily respiration rates decreased as application frequency increased and that rates were significantly higher in slurry-amended, compared to control treatments. Furthermore, the contribution of slurry-derived CO2 respiration increased as application frequency rose (from 37 to 68% between the first and fourth applications of HEI and from 58 to 80%, respectively, of COW). The labile fraction of potentially mineralizable slurry C, estimated with a first-order kinetic decomposition model, was also increased with application frequency. The two slurries differed in potentially mineralizable C during the 84 d after the application events. However, there were no differences between the two slurries in the potential mineralizable C (1.43% of applied C) that contributed to respiration after 84 d of application. This small residual effect has never been quantified before in an incubation experiment. This small residue C is very important to farm practices in which slurries are continuously applied for decades
Sensitivity analysis and calibration of CN-SIM to simulate the mineralisation of liquid dairy manures
No full textScientific knowledge of carbon and nitrogen dynamics incorporated into soil organic matter (SOM) dynamic simulation models can be tested using experimental data from decomposition experiments. This possibility is particularly interesting for liquid animal manures, which are very heterogeneous materials. CN-SIM is a SOM model that was successfully applied for the short- and long-term simulation of C and N dynamics in the soil. The objective of this research was to test this model using results of a 180-d laboratory incubation of five liquid dairy manures in three soils. Initial sensitivity analysis indicated that model parameters that mostly impact net CO 2 and soil mineral nitrogen concentration (SMN) are those that allocate manure C and N to model pools, their decomposition constants and soil parameters that describe microbial biomass and its residues. Automatic parameter optimisation was carried out with the downhill simplex method separately for 15 manure by soil combinations. After optimisation, CO 2 respiration was well simulated for the entire period, while SMN was overestimated after day 40. Simulations overestimated the remineralisation of immobilised N in the first weeks. Simulated initial microbial immobilisation was the only possibility for the model to match the experimental decrease of SMN, while simulated N remineralisation after day 40 was necessary to enable a good simulation of respired CO 2. Further work is needed to test whether these simulations can be improved by adding SMN sinks (such as denitrified N and clay-fixed ammonium)
Variations 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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Analisi della sensibilità e calibrazione multi-obiettivo di un modello per la mineralizzazione di reflui zootecnici
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