1,721,007 research outputs found
Soil organic matter formation is controlled by the chemistry and bioavailability of organic carbon inputs across different land uses
No full textSoil organic matter (SOM) formation involves microbial transformation of plant materials of various quality with physico-chemical stabilisation via soil aggregation. Land use and vegetation type can affect the litter chemistry and bioavailability of organic carbon (OC), and consequently influence the processing and stabilisation of OC into SOM. We used 13C nuclear magnetic resonance (13C NMR) and hot-water extraction to assess the changes in chemical composition and labile OC fractions during the transformation processes from leaf to litter to SOM depending on land use and vegetation type. The hot-water-extractable OC (HWEOC) decreased from leaf (43–65 g kg−1) to litter (19–23 g kg−1) to SOM (8–16 g kg−1) similar in four land use types: grassland, sugarcane, forest and banana. These trends demonstrated the uniform converging pathways of OC transformation and increasing stability by SOM formation. The preferential decomposition and decrease of labile OC fractions (∑% di-O-alkyl, O-alkyl and methoxyl) from leaf (54–69%) to SOM (41–43%) confirmed the increasing stability of the remaining compounds. Despite differences in the biochemical composition of the leaf tissues among the vegetation types, the proportions of labile OC fractions in SOM were similar across land uses. The OC content of soil was higher in forest (7.9%) and grassland (5.2%) compared to sugarcane (2.3%) and banana (3.0%). Consequently, the HWEOC per unit of soil weight was higher in forest and grassland (2.0 and 1.2 g kg−1 soil, respectively) compared to sugarcane and banana (0.3 and 0.4 g kg soil−1, respectively)
Changed by fire: linking carbon and energy fluxes by microbial decomposition of soil organic matter after frequent forest burning events
No full texthttp://dx.doi.org/10.13039/501100001655 DAADhttp://dx.doi.org/10.13039/501100018647 RUDN Universityhttp://dx.doi.org/10.13039/501100001809 National Natural Science Foundation of Chin
Nutrients Dynamics in Sugarcane Soils: Effects of Land Use and Management Practices
No full textSugarcane, as a worldwide cultivated commercial crop, has drawn a great attention towards its nitrogen (N) use efficiency as well as potential effects on associated watersheds. Particularly, there is an increasing concern about potential loss of carbon (C) and nitrogen from sugarcane fields and its environmental impacts on the Australian Great Barrier Reef catchments. Sugarcane field management practices play a vital role in refining soil C and N cycling and improving plant N use efficiency. The common management practices in sugarcane fields such as liming, legume intercropping, green harvest and burning have different effects on soil C and nutrients dynamic. To be specific, liming is widely used as an effective amendment to remediate soil acidity. Moreover, green harvest, which is known as trash blanket practice, is promoted in intensive cropping regions as decomposition of sugarcane trash can sequester C and N under the trash blanket layer. Although, previous studies had investigated the effects of liming and trash blanket on cropping fields, but the understandings of how liming and trash blanket affect Australian sugarcane cropping system, is largely unknown. Additionally, some studies have suggested that sugarcane compost may provide significant amounts of bioavailable C and N to sugarcane cropping system. However, different composition of compost have different influence on soil properties such as soil pH, soil C and N contents. The effects of compost on soil properties may also vary with its application methods as well as soil and vegetation type. Unfortunately, the scientific knowledge regarding the effects of composted sugarcane residue on Australia sugarcane fields remain uncertain.
Although several studies have reported the relationship between the soil nutrients cycle and field managements, the mechanistic understanding of how sugarcane field managements affect the N dynamics remained unclear. The objectives of this thesis were to determine: 1) the impacts of liming on the N availability and dynamics in tropical acidic sugarcane soils; and 2) the dynamics of soil C and N in sugarcane cropping fields after application of subsoil organic amendments to sugarcane soil. Two field experiments were designed to achieve these major goals, including: a) Impacts of liming on soil N dynamics in sugarcane fields in Bundaberg; b) Impact of subsoil organic amendments to sugarcane cropping system on long term soil physical, chemical and biological properties in Maryborough, Australia. It was hypothesized that: 1) liming practice in acidic soils would alter soil N dynamics as well as the abundance and activity of soil microorganisms; and 2) subsoil amendment of compost would contribute substantially to the labile C and N supply for soil microbial activity as well as plant uptake and consequently increase sugarcane yield.
In a field trial at Bundaberg, Australia, the adjacent sugarcane treatments of 26 months after liming (26ML), 14 months after liming (14ML) and no lime amendment (CK) were selected to investigate the effect of liming practice on soil N bioavailability and microbial activity in a long term subtropical sugarcane cropping system. Liming in both 14ML and 26ML treatments significantly increased soil pH (by 1.2-1.4 units) and exchangeable Ca2+ (> 2 folds) content compared with the CK treatment. The lower concentrations of hot water extractable organic C, total N and NH4+-N in the 14ML treatment compared to the CK and 26ML treatments, was attributed to the absence of trash blanket placement in the former and enhanced N immobilization, by soil microbial community, due to improved soil pH. Liming practice (14ML and 26ML) increased soil microbial biomass C and N contents, particularly in the presence of the trash blanket (26 ML treatment), while decreased soil respiration and qCO2, indicating that acidic stress conditions were relieved in the liming treatments. Soil pH value was shown to be the main factor governing soil enzyme activities, with an overall decrease in all enzyme activities in response to liming practice.
In a field trial at Yerra, Maryborough, Australia, Four subsoil amendment treatments, including no amendment as control (CK), gypsum subsoil application as calcium enriched treatment (GP), compost subsoil application as organic ameliorant treatment (CP) and mineral fertilizer subsoil application as fertilizer treatment (FE), were designed to investigate the effect of subsoil amendments on sugarcane soil health. The ameliorants were applied to the subsoil two weeks before sugarcane planting. At the end of the third ratoon harvest, the compost treatment showed a slightly higher soil pH compared to other three treatments. The concentration of NH4+-N in the CP treatment, at the 0-10 cm soil depth, was significantly higher than gypsum (GP) and mineral fertilizer (FE) amended treatments. This may be due to the higher N uptake at the sugarcane root zone (10-25 cm depth) in this treatment and consequently transport of higher amount of N to the topsoil through trash blanket decomposition after sugarcane harvest. The highest concentrations of hot water extractable organic C and N (HWEOC; HWETN) in the CP treatment (10-25 cm depth), can be attributed to the organic matter input and its decomposition within the compost application layer. Soil MBC and MBN contents (0-10 cm depth) generally tend to be higher in the CP treatment in comparison with the other treatments. This may be due to leaching of soluble organic C and N in this treatment, which provide an available energy source for utilization of soil microbial community. The CO2 respiration in the CP and FE treatments, were significantly higher than CK and GP treatments, while GP treatment showed the lowest CO2 respiration in the 10-25 cm depth. At soil depths below 25 cm, soil labile C becomes a limiting factor for soil CO2 respiration, which is supported by significant positive correlation found between HWEOC and soil CO2 respiration. Significant increase in sugarcane yield, over 4 years, has been observed in the CP compared to other treatments, which may be due to the increased labile C and N pools provided by the slow decomposition of subsoil-applied compost.Thesis (Masters)Master of Philosophy (MPhil)Griffith School of EnvironmentScience, Environment, Engineering and TechnologyFull Tex
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
Microbial responses to soil constraints as a measure of soil health in sugarcane and grain systems
No full textEnvironmental or human-induced disturbances, such as compaction and drought commonly caused by modern agricultural machinery and extreme climate events, have drawn great attention towards their impacts on soil microbial activities and associated declines in soil health and crop yield. To be specific, soil compaction combined with local extreme weather events, such as intensive rainfall or prolonged drought, may cause a significant decrease in soil microbial activity and threaten sustainable crop production. The use of organic amendment and crop rotation are commonly adopted as improved field management strategies to mitigate the disturbance-induced (compaction and drought) declines in crop yield, soil carbon, and soil health. Although widespread interest exists in the assessment of the detrimental impacts of environmental disturbances on agricultural systems, the response of belowground nutrient turnover processes to compaction and/or drought and how such responses are mediated by the microbial communities are less explored. In addition, there is a paucity of information on soil microbial responses to compaction and drought stresses and their recovery from the stressed conditions, particularly the differences in soils with conventional and improved management history. Furthermore, a robust, cheap, and easy-to-understand index needs to be developed in monitoring soil microbial community responses to compaction and drought stresses as current mainstream soil health indicators are expensive and complicated for end-users.This thesis aimed to investigate microbial responses to soil constraints as a measure of soil health in sugarcane and grain systems. The specific obj ctives of this thesis were to a) determine the mechanisms responsible for soils’ microbial functional response and its thresholds to environmental disturbance (compaction and drought); b) adopt this mechanism of the responses of soil microbial community following soil compaction (or drought) stress into both conventional and improved soil management practices contexts; c) generate soil resistance and resilience index based on the responses of soil microbes to compaction and/or drought ; d) enrich the knowledge of soil microbial activity and nutrient pools responses to different practices of removing compaction stress, such as deep trenching mill-mud application and shallow furrow application, in fields condition. Three incubation experiments and a field trial were designed to test following hypotheses: 1) Soil biological functions such as respiration and microbial biomass and activity are reliable indices for assessment of soil health and resilience to compaction and moisture (waterlogging or drought) stresses; 2) Soils with improved management practice history have higher resistance against compaction stress and higher resilience following removal of the stress; 3) Response pattern of soil microbial community to drought stress is highly related to the applied stress levels rather than the history of field management practices; 4) Application of organic amendments (e.g., crop residues, mill-mud) and removal of soil compaction stress would increase the size of soil microbial community and microbial activity (indicating soil resistance and resilience), which further improves soil health condition and increases crop yield. In the first incubation experiment, two contrasting sugarcane soils (Planosols at Rocky Point and Nitisols at Ingham) were exposed to a combination of compaction and drought stresses, and microbial functions were investigated going into the stress as well as their response coming out of the stress. We artificially applied a gradient of bulk densities (0.9 - 1.5 g cm-3) and water fill pore space (WFPS; 21% to 100%). Under high water content (i.e., WFPS of 47% to 100%), low compaction levels (1.1 and 1.2 g cm-3) increased soil cumulative microbial respiration in Planosols treatments by 18% in comparison to nil compaction treatment (0.9 g cm-3), while high compaction levels (1.3 - 1.5 g cm-3) decreased soil cumulative microbial respiration by 25% with increasing of compaction stress in 74 days incubation experiments. In contrast, in Nitisols with high water content, the highest compaction treatment (1.5 g cm-3) significantly increased soil cumulative microbial respiration by 12% in comparison to nil treatment (0.9 g cm-3). Our data revealed that the Nitisols had a higher resistance index of microbial C use efficiency, while the Planosols had a higher resilience index of microbial C use efficiency to compaction and moisture stresses. This could be attributed to greater aggregation potential (associated with more finely textured particles), and higher diversity of the microbial community in the Nitisols, which provide higher functional stability to resist environmental disturbance, while fast drainage and higher adaptation of microbial communities in the Planosols would provide a faster recovery from the applied stresses. This also indicates that soil microbial responses to compaction stress are governed by soil texture and moisture status. In the second incubation experiment, Nitisols with conventional and improved management history from adjacent sugarcane farms at Foresthome, North Queensland, Australia, were exposed to compaction stress (1.4 g cm-3), and microbial functions were investigated during compaction and ploughing cycle as well as their response to surface and mixing plant residue application methods over 70 days. The improved management block was managed with minimum tillage, mound planting, and legume plantation in comparison to conventional furrow management. Compaction was applied at the commencement of the experiment and removed at day 28 via plant residue application combined with ploughing. Overall, the concentration of labile C was 42% higher in treatments with improved management history. Within treatments with the same management history, the treatments with ploughing practice following compaction stress generated the highest cumulative and net cumulative CO2 emissions, followed by compaction-only and ploughing-only treatments. Interestingly, we found that legume residue incorporation along with improved land management minimized fluctuation of net cumulative CO2 emissions between compacted and non-compacted treatments by the end of experiment; however, we did not find the same pattern in treatments with conventional land management. Our results revealed that different field management practices might not alter soil microbial response patterns to compaction stress as microbial activity is mainly governed by water content and water fill pore space. Improved field management practices can improve soil resistance and resilience to compaction stress, which is shown as a faster stabilization of microbial properties after compaction stress and its removal due to their higher organic matter content and complexity of microbial community. The present study confirmed that application of legume residue increased the supply of organic C and N for soil microbial community, enhanced the nutrient cycling processes, and improved soil health status. In the third incubation experiment, Planosols collected from Wickepin, Western Australia (one soil with conventional management history and one soil with improved management history) were exposed to severe, moderate and nil drought stress and microbial functions were investigated going into stress as well as their response coming out of stress via rewetting and plant residue input. In general, treatments with improved management history had higher (15% - 53%) cumulative CO2 respiration in comparison to treatments with conventional management throughout the incubation period without plant residue amendment. In addition, drought stress significantly decreased cumulative CO2 respiration regardless of soil management history. We found that the differences of cumulative CO2 emissions decreased at day 56 but increased at the end of experiment (day 70) in both drought stressed treatments with conventional management history. The hot water extractable organic C pool was highly related (r = 0.56 - 0.78) to the umulative CO2 respiration and microbial activity. The results showed that different field management practices may not change soil microbial response patterns to drought, as microbial activity is mainly governed by soil texture when water content is limited. Improved field management could help to build soil resilience to drought, which is shown as the tolerance to moderate drought and resistance to severe drought due to their high organic matter content and complexity of microbial community. However, soil under conventional field management would have a lower resistance, but higher recovery to drought stress. The plant residue application increased the concentration of microbial biomass and enzyme activity via increasing labile C and nutrients contents regardless of soil management history. A field trial was conducted at Burdekin, Australia, to investigate the effects of different decompaction field managements on soil nutrient cycling, associated biological activities, and sugarcane yield. This experiment included four treatments comprising: control (CK, without mill-mud), mill-mud shallow furrow (MS), deep trench without mill-mud (DT), and deep trench mill-mud application (MD). Overall, the application of mill-mud significantly improved soil organic matter and nutrient content. Surface millmud application increased the concentration of soil Colwell P six-fold in comparison to the control. Deep trench application of mill-mud increased concentrations of hot water extractable organic C by 30% - 70% and hot water extractable total N by 30% - 90% at the application depth (ca. 20 cm depth). Soil microbial biomass C and N were also higher in mill-mud applied layers (ca. 20 cm depth). As expected, in comparison to the control, mill-mud applied treatments increased plant cane yield by 7% (MS treatment) and 14% (MD treatment). The deep trench without mill-mud (DT) practice also increased the plant cane yield by 11% compared to the control, which may be due to the release of native organic C and improved soil health. Deep trench combined with the mill-mud application (MD) increased the supply of organic C and N and nutrients to the microbial community within the entire soil profile, enhanced nutrient cycling processes and soil health for sugarcane growth, and thus increased sugarcane productivity. In the presented thesis, soil microbial responses to two main soil constraints (compaction and drought) under different soil textures, vegetation type and field management history were investigated. Based on the presented result, soil texture and WFPS played vital roles in regulating microbial responses to compaction and drought. The finer soil texture provided a better and stable microbial habitat and WFPS governed the diffusion of soil labile C and nutrients for microbial growth. In addition, field managements such as organic matter amendment and/or ploughing would stimulate microbial responses to soil constraints as organic amendment would directly increase soil organic matter content and ploughing would adjust soil WFPS. Also, these two factors are intensively linked to crop yield as increased sugarcane yield was found in organic matter applied and ploughed treatments, particularly in ploughed only treatment. Additionally, the presented study found that the soil microbial community had higher tolerance to soil disturbances under improved field management history than conventional management history, which could be attributed to the complexity of microbial community structure established through long term improved field management. However, microbial community structure and key functional gene analysis are needed to confirm this statement. In conclusion, application of molecular biology approaches would further increase the potential of using microbial responses to soil constraints as a measure of soil health and generate a comprehensive index in monitoring soil health in the long run.Thesis (PhD Doctorate)Doctor of Philosophy (PhD)School of Environment and ScScience, Environment, Engineering and TechnologyFull Tex
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
- …
