1,721,054 research outputs found
Exponential response of nitrous oxide (N2O) emissions to increasing nitrogen fertiliser rates in a tropical sugarcane cropping system
No full textHigh rainfall, irrigation and large fertiliser nitrogen (N) inputs create conditions highly conducive for nitrous
oxide (N2O) emissions in sugarcane systems. A positive non-linear response of N2O emissions to increasing N
fertiliser rates has been reported from a range of cropping systems, where N inputs exceed crop requirements.
However, the response of N2O emissions to N fertiliser rates in sugarcane remains largely unclear. This study
monitored N2O emissions in a tropical sugarcane system in Australia to examine the response of N2O emissions to
increasing N fertiliser application rates. Soil-borne N2O emissions were measured at high temporal resolution
with an automated monitoring system across four N fertiliser treatments (0, 150, 200 and 250 kg N ha 1). Furrow
irrigation and rainfall events triggered large N2O emissions with peak N2O emissions >100 g N ha-1 d 1. Nitrous
oxide emissions peaked when high soil nitrate (NO3-) content (>40 kg N ha 1) coincided with water-filled pore
space (WFPS) near saturation. Emissions of N2O in the first three months after N fertilisation accounted for 74–96
% of total N2O emitted over the year. Cumulative N2O emissions increased exponentially with N fertiliser rates,
ranging from 0.29 to 3.06 kg N ha 1. Emission factors (EF) ranged from 0.69 to 1.11 %, exceeding the IPCC
default of 1 % at 250 kg N ha 1 of N rate. The amount of N2O emitted per kg sugar yield doubled above the
recommended N rate of 200 kg N ha 1. The exponential response of N2O to fertiliser N suggests that N2O
emissions from intensive sugarcane systems with high fertiliser N inputs are considerably larger than currently
assumed and that a non-linear model may be more appropriate for estimating N2O emissions from sugarcane
soils. The steep increase in N2O intensity demonstrates environmental inefficiency at high fertiliser N rates,
emphasising the importance of avoiding excessive N fertiliser application in tropical sugarcane systems from
both agronomic and environmental perspectives
No sugar yield gains but larger fertiliser 15N loss with increasing N rates in an intensive sugarcane system
No full textInfluence of historic land use change on the biosphere-atmosphere-exchange of C and N trace gases in the humid, subtropical region of Queensland
No full textIncreases in atmospheric concentrations of the greenhouse gases (GHGs) carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) due to human activities have been linked to climate change. GHG emissions from land use change and agriculture have been identified as significant contributors to both Australia’s and the global GHG budget. This is expected to increase over the coming decades as rates of agriculture intensification and land use change accelerate to support population growth and food production. Limited data exists on CO2, CH4 and N2O trace gas fluxes from subtropical or tropical soils and land uses. \ud
To develop effective mitigation strategies a full global warming potential (GWP) accounting methodology is required that includes emissions of the three primary greenhouse gases. Mitigation strategies that focus on one gas only can inadvertently increase emissions of another. For this reason, detailed inventories of GHGs from soils and vegetation under individual land uses are urgently required for subtropical Australia.\ud
This study aimed to quantify GHG emissions over two consecutive years from three major land uses; a well-established, unfertilized subtropical grass-legume pasture, a 30 year (lychee) orchard and a remnant subtropical Gallery rainforest, all located near Mooloolah, Queensland. GHG fluxes were measured using a combination of high resolution automated sampling, coarser spatial manual sampling and laboratory incubations. Comparison between the land uses revealed that land use change can have a substantial impact on the GWP on a landscape long after the deforestation event. \ud
The conversion of rainforest to agricultural land resulted in as much as a 17 fold increase in GWP, from 251 kg CO2 eq. ha-1 yr-1 in the rainforest to 889 kg CO2 eq. ha-1 yr-1 in the pasture to 2538 kg CO2 eq. ha-1 yr-1 in the lychee plantation. This increase resulted from altered N cycling and a reduction in the aerobic capacity of the soil in the pasture and lychee systems, enhancing denitrification and nitrification events, and reducing atmospheric CH4 uptake in the soil.\ud
High infiltration, drainage and subsequent soil aeration under the rainforest limited N2O loss, as well as promoting CH4 uptake of 11.2 g CH4-C ha-1 day-1. This was among the highest reported for rainforest systems, indicating that aerated subtropical rainforests can act as substantial sink of CH4. \ud
Interannual climatic variation resulted in significantly higher N2O emission from the pasture during 2008 (5.7 g N2O-N ha day) compared to 2007 (3.9 g N2O-N ha day), despite receiving nearly 500 mm less rainfall. Nitrous oxide emissions from the pasture were highest during the summer months and were highly episodic, related more to the magnitude and distribution of rain events rather than soil moisture alone. \ud
Mean N2O emissions from the lychee plantation increased from an average of 4.0 g N2O-N ha-1 day-1, to 19.8 g N2O-N ha-1 day-1 following a split application of N fertilizer (560 kg N ha-1, equivalent to 1 kg N tree-1). The timing of the split application was found to be critical to N2O emissions, with over twice as much lost following an application in spring (emission factor (EF): 1.79%) compared to autumn (EF: 0.91%). This was attributed to the hot and moist climatic conditions and a reduction in plant N uptake during the spring creating conditions conducive to N2O loss. \ud
These findings demonstrate that land use change in subtropical Australia can be a significant source of GHGs. Moreover, the study shows that modifying the timing of fertilizer application can be an efficient way of reducing GHG emissions from subtropical horticulture
Non-linear response of soil N2O emissions to nitrogen fertiliser in a cotton-fallow rotation in sub-tropical Australia
Get PDFNitrogen (N) fertiliser is a major source of atmospheric nitrous oxide (N<sub>2</sub>O), and over recent years there has been growing evidence for a non-linear, exponential relationship between N fertiliser application rate and N<sub>2</sub>O emissions. However, there is still a high level of uncertainty around the relationship of N fertiliser rate and N<sub>2</sub>O emissions for many cropping systems. We conducted year-round measurements of N<sub>2</sub>O emission and lint yield in four N-rate treatments (0, 90, 180 and 270 kg N ha<sup>–1</sup>) in a cotton–fallow rotation on a black vertosol in Australia. We observed a non-linear exponential response of N<sub>2</sub>O emissions to increasing N fertiliser rates with cumulative annual N<sub>2</sub>O emissions of 0.55, 0.67, 1.07 and 1.89 kg N ha<sup>–1</sup> for the four respective N fertiliser rates, but no N response to yield occurred above 180 kg N ha<sup>–1</sup>. The annual N<sub>2</sub>O emission factors induced by N fertiliser were 0.13, 0.29 and 0.50% for the 90, 180 and 270 kg N ha<sup>–1</sup> treatments respectively, significantly lower than the IPCC Tier 1 default value of 1.0%. This nonlinear response suggests that an exponential N<sub>2</sub>O emissions model may be more appropriate for estimating emission of N<sub>2</sub>O from soils cultivated to cotton in Australia. It also demonstrates that improved agricultural N-management practices can be adopted in cotton to substantially reduce N<sub>2</sub>O emissions without affecting yield
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
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
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