1,720,969 research outputs found
Biochemical origin and refractory properties of humic acid extracted from the maize plant
No full textHumic acids (HA) contribute to soil fertility because of their chemical, physical, and biological properties. The origin of HAs in soils has puzzled scientists for decades, and what HAs are and what their origin is remain unclear. The isolation of HAs in plants, which have characteristics close to soil HAs, suggests the probable origin of soil-HA is the preservation of plant tissue, indicating biochemical origin. In this paper HA from maize plant at different stages of maturity is isolated, from which it was found that the evolution of this fraction depends on and is derived from cell wall formation. Evidence was also found that HA was above all composed of lignin and cutin residues, and was characterized by low surface area. After 8 months of incubation in both mineral-artificial and natural soils, humic acid isolated form maize plant could be recovered intact
Humic acid formation in artificial soils amended with compost at different stages of organic matter evolution
Full text linkA composting process was conducted under optimal conditions for 150 d, obtaining three biomasses at different levels of maturity: raw material (RM), fresh compost obtained after 11 d of composting (FC), and evolved compost (EC) obtained after 150 d of composting. During the composting process, HAs were extracted and fully characterized by mass balance, DRIFT, and 1H and 13C-nuclear magnetic resonance spectroscopy. Each compost sample was incubated for 180 d in an artificial soil, after which HA extraction was repeated and characterized. To compare composts containing different amounts of labile organic matter (OM), an equal amount of unhydrolyzable OM was added to the soils. Our results indicated that compost HAs consist of a biologically and chemically stable fraction (i.e., the unhydrolyzable HA [U-HA]) and a labile fraction, whose relative contents depended on the composting duration. Humic acid from more EC contained a higher amount of recalcitrant fraction (aromatic carbon) and a lesser amount of labile fraction (aliphatic carbon) than HA from RM and FC. These results suggest that the humification process during composting preserves the more recalcitrant fraction of the compost-alkali soluble/acid insoluble fraction (HA-fraction). Incubation of composts in soil showed that due to the higher labile fraction content, HAs from raw material were more degraded than those from EC. The abundance of labile carbon of soil amended with less-evolved compost (RM and FC) allowed the more recalcitrant fractions of U-HA to be more preserved than in EC. These results suggest that less-evolved compost could contribute more than well evolved compost to the stable soil OM. Copyrigh
The impact of crop plant residues on carbon sequestration in soil : a useful strategy to balance the atmospheric CO2
No full textAnthropogenic emission of CO2 and other greenhouse gases was rapidly increased with the Industrial Revolution and this event has caused a world interest in identifying strategies of reducing the rate of gaseous emission. The intergovernmental Panel on Climate Change shows that from 1850 and 1998 the emission from terrestrial ecosystem was about half of fossil fuel combustion. Agriculture can be a source or sink for atmospheric CO2 because soil organic carbon pool (SOCP) in soil surface is sensitive to changes in land use and soil management practice. The carbon sink capacity of the world agricultural and degraded soils is 50-66% of the historic carbon loss that are of 42 to 78 Gt of carbon respectively. Carbon (C) sequestration implies transferring atmospheric CO2 into long-lived pools and subsequent storage of fixed C as soil organic carbon (SOC). In this way the conservation of plant residues in agricultural soil play an important role in CO2 sequestration. The mechanism by which crop residues contribute to SOC is through their chemical, phisical and biological stabilization. In this chapter we discussed the role of the plant residues in the carbon sequestration throughout plant tissue stabilization in soil, giving a new approach and understanding of the plant residue conservation in soil
Carbon sequestration in soil: the role of the crop plant residues
No full textAnthropogenic emission of CO2 and other greenhouse gases was rapidly increased with the Industrial Revolution and this event has caused a world interest in identfying strategies of reducing the rate of gaseous emission.The intergovernmental Panel on Climate Change shows that from 1850 and 1998 the emission from terrestrial ecosystem was about half of fossil fuel combustion.Agriculture can be a source or sink for atmospheric CO2 because soil organic carbon pool (SOCP) in soil surface is sensitive to changes in land use and soil management practice. The carbon sink capacity of the world agricultural and degraded soils, is 50-66% of the historic carbon loss that are of 42 to 78 Gt of carbon respectively.Carbon (C) sequestration implies transferring atmospheric CO2 into long-lived pools and subsequent storage of fixed C as soil organic carbon (SOC). In this way the conservation of plant residues in agricultural soil play an important role in CO2 sequestration. The mechanism by which crop residues contribute to SOC is through their chemical, phisical and biological stabilization. In this chapter we discussed the role of the plant residues in the carbon sequestration throughout plant tissue stabilization in soil, giving a new approach and understanding of the plant residue conservation in soil
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
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
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