1,721,156 research outputs found
Tillage impact on soil erosion by water: Discrepancies due to climate and soil characteristics
No full textNo-tillage (NT) is promoted for soil and water conservation, but research
findings on overland
flow and
soil erosion are inconsistent across different ecosystems, with some studies showing no benefits of NT
over conventional tillage (CT). A global literature review was conducted to quantify the impact of NT on
water runoff, sediment concentration and soil losses. The objective was to identify the underlying causes
of the variability in the performance of NT across different environments. Data from 282 paired NT and CT
runoff plots from 41 research studies worldwide were analysed using meta-analysis and principal
component analysis (PCA). Sediment concentration and soil losses were 56 and 60% lower under NT than
CT, respectively. These tended to be greater under CT than NT on long plots (90% for sediment
concentration and 94% for soil losses) and steepest slopes (79 and 77%, respectively). Greater differences
in sediment concentration and soil losses between NT and CT were observed in low clay soils and under
temperate climates. While on average there were no differences on runoff coefficient, NT decreased
runoff coefficient by about 40% compared to CT in mulched soils, under cool climate (<10 C), and for
experiments done >5 years. Overall, the results indicated that NT has greater potential to reduce runoff
and soil losses in temperate regions where soils of peri-glacial influence are relatively young, moderately
weathered and fragile compared to the heavily weathered clayey tropical soils that are well aggregated
and less erodible. The results of this study are expected to inform scientists, practitioners and policy
makers on the links between land management and soil functioning processes. Policy makers and
development implementers will be able to make informed choices of land management techniques for
effective NT implementation, for instance by having more mulch input under warm climates
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Selective organic carbon losses from soils by sheet erosion and main controls
No full textAlthough the impact of sheet erosion on the selective transportation of mineral soil particles has beenwidely investigated,
little is yet known about the specific mechanisms of organic carbon (OC) erosion, which constitutes an important link in the global
carbon cycle. The present study was conducted to quantify the impact of sheet erosion on OC losses from soils. Erosion plots with
the lengths of 1- and 5-m were installed at different topographic positions along a hillslope in a mountainous South African region.
A total of 32 rainfall events from a three years period (November 2010 up to February 2013), were studied and evaluated for runoff
(R), particulate and dissolved organic carbon (POCL and DOCL). In comparison to the 0–0·05m bulk soil, the sediments from the
1-m plots were enriched in OC by a factor 2·6 and those from the 5-m long plots by a factor of 2·2, respectively. These findings suggest
a preferential erosion of OC. In addition, total organic carbon losses (TOCL) were incurred mainly in particulate form (~94%) and the
increase in TOCL from 14·09 ± 0·68 g C m 1 yr 1 on 1-m plots to 50·03 ± 2·89 g C m 1 yr 1 on 5-m plots illustrated an increase in
sheet erosion efficiency with increasing slope length. Both TOCL and sediment enrichment in OC correspondingly increased with a
decrease in soil basal grass cover. The characteristics of rainstorms had no significant impact on the selectivity of OC erosion. The
results accrued in this study investigating the links between sheet erosion and OC losses, are expected to be of future value in the
generation of carbon specific erosion models, which can further help to inform and improve climate change mitigation measures.
Copyright © 2016 John Wiley & Sons, Ltd
Overgrazing decreases soil organic carbon stocks the most under dry climates and low soil pH: A meta-analysis shows
No full textGrasslands occupy about 40% of the world’s land surface and store approximately 10% of the global soil
organic carbon (SOC) stock. This SOC pool, in which a larger proportion is held in the topsoil (0–0.3 m), is
strongly influenced by grassland management. Despite this, it is not yet fully understood how grassland
SOC stocks respond to degradation, particularly for the different environmental conditions found
globally. The objective of this review was to elucidate the impact of grassland degradation on changes in
SOC stocks and the main environmental controls, worldwide, as a prerequisite for rehabilitation. A
comprehensive meta-analysis was conducted using 55 studies with 628 soil profiles under temperate,
humid, sub-humid, tropical and semi-arid conditions, to compare SOC stocks in the topsoil of nondegraded
and degraded grassland soils. Grassland degradation significantly reduced SOC stocks by 16% in
dry climates (1000 mm) and Asia was the most affected
continent ( 23.7%). Moreover, the depletion of SOC stock induced by degradation was more pronounced
in sandy (<20% clay) soils with a high SOC depletion of 10% compared to 1% in clayey ( 32% clay) soils.
Furthermore, grassland degradation significantly reduced SOC by 14% in acidic soils (pH
5), while SOC
changes were negligible for higher pH. Assuming that 30% of grasslands worldwide are degraded, the
amount of SOC likely to be lost would be 4.05 Gt C, with a 95% confidence between 1.8 and 6.3 Gt C (i.e.
from 1.2 to 4.2% of the whole grassland soil stock). These results by pointing to greater SOC losses from
grasslands under dry climates and sandy acidic soils allow identification of grassland soils for which SOC
stocks are the most vulnerable, while also informing on rehabilitation measure
Variations on the Author
Get PDF“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
Get PDFWe 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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Variation for agronomic traits, biomass allocation, and carbon storage in sorghum (sorghum bicolor [L.] moench) genotypes.
No full textMasters Degree. University of KwaZulu-Natal, Pietermaritzburg.Sorghum (Sorghum bicolor [L.] Moench, 2n = 2x = 20) is an ancient grain crop of Africa
cultivated worldwide. The productivity of sorghum is low (< 1.5 t/ha) under smallholder
farming systems in the region due to severe drought stress, poor soil health, diseases, insect
pests, and noxious weeds. Besides its grain production for food, feed, and industrial raw
materials, sorghum produces relatively high biomass for the biofuel and bioplastic industry.
Sorghum’s high biomass production can transfer atmospheric carbon (C) to the soil throughout
its growth stages, thereby enhancing soil fertility and crop productivity through atmospheric C
sequestration. There is a need to select sorghum genotypes with optimised agronomic traits,
high biomass production and water and nutrient use efficiencies to enhance economic yield and
carbon sequestration capacity. Therefore, the overall aim of this study was to screen and select
sorghum genotypes with better agronomic traits, biomass allocation, and C storage. The
specific objectives of the study were:
i. to quantify the extent of variation in biomass allocation and C storage between
major crops, including sorghum for crop production, and C sequestration potential
through a meta-analysis.
ii. to assess agronomic performance, biomass production and carbon accumulation in
selected sorghum genotypes for production and breeding.
iii. to assess the extent of genetic variability for agronomic and carbon storage traits in
selected sorghum genotypes to identify the best candidates for production or
breeding.
iv. to assess the trend and magnitude of relationships between agronomic and carbon
storage traits in sorghum to identify grain yield and carbon storage contributing
traits and to guide future sorghum variety development and release.
A metanalysis was conducted from 40 global studies that reported on the allocation of plant
biomass and C between roots and shoots of sorghum, maize, and wheat cultivars. Key statistics
were calculated to determine the variability among the cultivars for total plant biomass (PB),
shoot biomass (SB), root biomass (RB), root-to-shoot biomass ratio (RS), total plant carbon
content (PCc), shoot carbon content (SCc), root carbon content (RCc), total plant carbon stock
(PCs), shoot carbon stock (SCs), root carbon stock (RCs), and root-to-shoot carbon stock ratio
(RCs/SCs). Maize exhibited the highest variability for PB (with a coefficient of variation [CV]
of 31.2% and a mean of 4.2±1.3 Mg ha-1 yr-1), followed by wheat (CV of 24.2% and mean of
1.5±0.4 Mg ha-1 yr-1) and sorghum (16.8% and 2.0±0.8 Mg ha-1), respectively. A similar trend
was observed for PCs, with maize (CV of 40.1% and mean of 1.6±0.7 Mg ha-1) showing the
highest total plant C stock variability, followed by wheat (24.4% and 0.2±0.1 Mg ha-1), and
sorghum (16.3% and 0.9±0.3 Mg ha-1), respectively. Maize exhibited the highest variability for
RS (with a CV of 24.4% and mean of 0.1±0.03), while wheat exhibited the highest variability
for RCs/SCs (30.92% and 0.2±0.05). The meta-analysis revealed that maize and sorghum have
the highest variability for total plant biomass and plant carbon stocks, while wheat exhibits the
highest variability for the below-ground biomass and carbon stocks.
In the first experiment, 50 sorghum genotypes were evaluated using a 5 x 10 alpha lattice design
with two replications at three locations (Silverton, Ukulinga, and Bethlehem) in South Africa
during the 2022/23 growing season. The following agronomic and carbon storage traits were
assessed: days to 50% heading (DTH), days to 50% maturity (DTM), plant height (PH), PB,
SB, RB, RS, GY, HI, GCc, SCc, RCc, PCs, SCs, RCs, RCs/SCs, and grain carbon stock (GCs).
A combined analysis of variance revealed significant (P < 0.05) genotype x location interaction
for DTH, DTM, PH, PB, SB, RB, RS, and GY. Genotypes AS115, AS251, and AS134 were
the best performing with the highest GY of 5.08 g plant-1, 21.83 g plant-1, and 21.42 g plant-1,
respectively. Genotypes AS122 and AS27 ranked first and second, respectively, for all the
carbon stock parameters except for RCs, whereas genotype AS108 had the highest RCs of 8.87
g plant-1. The principal component analysis identified GY, DTH, PH, PB, SB, RB, RCs,
RCs/SCs, PCs, SCs, and GCs as the most discriminated traits among the test genotypes. The
cluster analysis using agronomic and carbon-related parameters delineated the test genotypes
into three genetic groups. The selected sorghum genotypes are recommended for further
breeding and variety release adapted to various agroecologies in South Africa.
Data from field experiments were computed to deduce variance components, heritability, and
genetic advance to guide genotype selection. Higher phenotypic coefficient of variation (PCV)
were recorded for PH (68.91%), followed by GY (51.8%), RB (50.51%), RS (41.96%),
RCs/SCs (44.90%), and GCs (41.90%). In contrast, higher genotypic coefficient of variations
(GCV) were recorded for GY (45.92%), followed by RB (39.24%), RCs/SCs (38.45), and RCs
(34.62). The high PCV and GCV values suggest the availability of genetic variability among
the test genotypes for the assessed traits. High to moderate broad-sense heritability and genetic
advance were observed for HI (83.76 and 24.53%), GY (78.59 and 9.98%), PB (74.14 and
13.18%) and PCs (53.63 and 37.57%), respectively, suggesting a marked genetic contribution
to the traits. High broad-sense heritability combined with increased genetic advance were
computed for PB, RB, GY, HI, RS, GCs, RCs, and RCs/SCs, indicating that genetic effects
primarily control these traits.
In the third experimental chapter, correlation and path coefficient analyses were computed to
discern the trend and magnitude of associations of assembled traits to guide simultaneous
selection for enhanced grain yield, its components and carbon storage. Significant (P < 0.05)
positive phenotypic and genotypic correlations were observed between GY with HI at r = 0.79
and r = 0.76, DTH (r = 0.31 and r = 0.13), PH (r = 0.27 and r = 0.1), PB (r = 0.02 and r = 0.01),
RB (r = 0.06 and r = 0.05), respectively. Further, the path analysis revealed significant positive
direct effects of SB (0.61) and RB (0.46) on GY. The RS exerted a positive significant
genotypic indirect effect (0.26) on GY through SB. The overall association analyses revealed
that PB, SB, RB, RS, RCs, and RCs/SCs significantly influenced GY performance and are the
principal traits when selecting sorghum genotypes with high carbon storage capacity.
The present study identified the following promising genotypes: AS251, SS27, AS134, AS203,
and AS563 for their high biomass production, grain yield, and C sequestration potentials. The
identified genotypes could be advanced for cultivar development and further evaluated for net
carbon contribution to the soil
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