Greenhouse gas abatement on southern Australian grains farms: B iophysical potential and financial impacts

The agricultural sector generates a substantial proportion of global greenhouse gas (GHG) emissions through emissions of carbon dioxide (CO2) and nitrous oxide (N2O). Changes to agricultural practices can provide GHG abatement by maintaining or increasing soil organic carbon (SOC) stored in soils or vegetation, or by decreasing N2O emissions. However, it can be difficult to identify practices that achieve net abatement because practices that increase SOC stocks may also increase N2O emissions from the soil. This study simulated the net on-farm GHG abatement and gross margins for a range of management scenarios on two grain farms from the western and southern grain growing regions of Australia using the Agricultural Production Systems sIMulator (APSIM) model. The soils and practices selected for the study were typical of these regions. Increased cropping intensity consistently provided emissions reductions for all site-soil combinations. The practice of replacing uncropped or unmanaged pasture fallows with a winter legume crop was the only one of nine scenarios to decrease GHG emissions and increase gross margins relative to baseline practice at both locations over the 100-year simulation period. The greatest abatement was obtained by combining this practice with an additional summer legume crop grown for a short period as green manure. However, adding the summer legume decreased farm gross margins because the summer crop used soil moisture otherwise available to the following cash crop, thus reducing yield and revenue. Annual N2O emissions from the soil were an order of magnitude lower from sandy-well-drained soils at the Western Australian location (Dalwallinu) than at the other location (Wimmera) with clay soil, highlighting the importance of interactions between climate and soil properties in determining appropriate GHG abatement practices. Thus, greatest abatement at Dalwallinu was obtained from maintaining or increasing SOC, but managing both N2O emissions and SOC storage were important for providing abatement at Wimmera

Mitochondrial haplotypes reveal low diversity and restricted connectivity of the critically endangered batoid population in a Marine Protected Area

Stability and long-term persistence of a species rely heavily on its genetic diversity, which is closely allied to its capacity for adaptation. In threatened species, population connectivity can play a major role in maintaining that diversity, and genetic assessments of their populations can be crucial for the design of effective spatial conservation management. Not only is it worth evaluating the amount of diversity in a candidate population for protection, but the magnitude of outgoing gene flow can provide insight into its potential to replenish others via emigrants. The critically endangered flapper skate Dipturus intermedius receives protection in the Loch Sunart to the Sound of Jura Marine Protected Area (MPA) in Scotland. However, there is insufficient knowledge of genetic diversity and connectivity across its range. Recent tagging studies in the MPA suggest the presence of animals with high levels of site fidelity and residency, as well as transient individuals, raising concerns of limited connectivity to populations beyond the MPA. In this study, a newly developed mitochondrial haplotype marker allowed use of DNA sourced from fin clips, mucus and egg cases to investigate population structure and mitochondrial variability across several sites around the British Isles, including the MPA. Unfortunately, results characterized the MPA as having particularly low haplotype diversity and significant population differentiation from other sample sites. More than a quarter of its individuals carry a haplotype rarely observed elsewhere, leaving outgoing gene flow questionable. The MPA appears unlikely to sustain the species{\textquoteright} existing mtDNA genetic diversity or act as an effective source population

Modelling nitrogen leaching : are we getting the right answer for the right reason?

The complexities and challenges in quantifying N leaching have led to development of a range of measurement and modelling techniques, but none are widely applied. Observations that N moves more slowly than water through the soil profile has resulted in different approaches being used to simulate impeded N movement in crop models: (i) by accounting for nitrate NO−3 adsorption to the soil, (ii) by considering incomplete mixing between resident and draining soil water fractions or (iii) a combination of both.We compare and discuss strengths and weaknesses of these approaches. Our inability to directly measure model parameters (especially with regards to simulating N dynamics), and the risk of compensating errors during model testing and calibration, often results in low confidence in simulated N leaching. We caution that our current ability to simulate N leaching is in most cases not yet well enough developed for reliable and accurate predictions. We recommend a more strategic approach involving better linking measurement and modelling to improve understanding of the critical soil processes that control N leaching as one way of further improving our understanding and quantification of N leaching.http://www.elsevier.com/locate/agwathb201

Impact of sugarcane trash on fertilizer requirements for São Paulo, Brazil

The area under mechanized sugarcane (Saccharum spp.) harvesting is expanding in Brazil, increasing the return of trash to the soil. The main questions regarding this management are: (i) after adopting unburned mechanical harvesting, how long will it take to observe decreases in fertilizer requirements, (ii) what will be the magnitude of this decrease and, (iii) the impact in the short run of removing trash for energy purposes in the nutrient cycling? This study aimed to build an N prediction model for long term assessment of the contribution of sugarcane crop residues to sugarcane nutrition and to evaluate the cycling of other nutrients derived from crop residues. Keeping crop residues over the soil will increase soil N stock and N recovery by sugarcane, reaching equilibrium after 40 years with recovery of approximately 40 kg ha-1 year-1 of N. Removing trash for energy production will decrease the potential reduction in N fertilizer requirement. Of the total nutrients in the trash, 75 % of the K2O (81 kg ha-1 year-1) and 50 % of the N (31 kg ha-1 year-1) are in the tops, indicating the importance of maintaining tops in the soil to sustain soil fertility. Because the input data employed in the simulations are representative of the conditions in Southeast Brazil, these results might not be definitive for situations not represented in the experiments used in the study, but the model produced is useful to forecast changes that occur in the soil under different trash management

Soil Organic Carbon and Nitrogen Feedbacks on Crop Yields under Climate Change

Articles in A&EL are published under the CC-BY NC ND (non-commercial; no derivatives) license (https://creativecommons.org/licenses/by-nc-nd/2.0/). Users are free to copy and redistribute the material in any medium or format. Any further publication of the article will require proper attribution; no derivative works may be made from this article; and the article may not be used for any commercial gain (https://creativecommons.org/licenses/by-nc-nd/2.0/). The author is given explicit permission to publish the final article in her/his institutional repository. There is an option for the CC-BY license if required by an author's institution.Peer reviewedPublisher PD

Number needed to treat with ursodeoxycholic acid therapy to prevent liver transplantation or death in primary biliary cholangitis

Objective: The clinical benefit of ursodeoxycholic acid (UDCA) in primary biliary cholangitis (PBC) has never been reported in absolute measures. The aim of this study was to assess the number needed to treat (NNT) with UDCA to prevent liver transplantation (LT) or death among patients with PBC. Methods: The NNT was calculated based on the untreated LT-free survival and HR of UDCA with respect to LT or death as derived from inverse probability of treatment weighting-adjusted Cox proportional hazard analyses within the Global PBC Study Group database. Results: We included 3902 patients with a median follow-up of 7.8 (4.1-12.1) years. The overall HR of UDCA was 0.46 (95% CI 0.40 to 0.52) and the 5-year LT-free survival without UDCA was 81% (95% CI 79 to 82). The NNT to prevent one LT or death within 5 years (NNT5y) was 11 (95% CI 9 to 13). Although the HR of UDCA was similar for patients with and without cirrhosis (0.33 vs 0.31), the NNT5y was 4 (95% CI 3 to 5) and 20 (95% CI 14 to 34), respectively. Among patients with low alkaline phosphatase (ALP) (≤2× the upper limit of normal (ULN)), intermediate ALP (2-4× ULN) and high ALP (>4× ULN), the NNT5y to prevent one LT or death was 26 (95% CI 15 to 70), 11 (95% CI 8 to 17) and 5 (95% CI 4 to 8), respectively. Conclusion: The absolute clinical efficacy of UDCA with respect to LT or death varied with baseline prognostic characteristics, but was high throughout. These findings strongly emphasise the incentive to promptly initiate UDCA treatment in all patients with PBC and may improve patient compliance

Input of sugarcane post-harvest residues into the soil

Sugarcane (Saccharum spp.) crops provide carbon (C) for soil through straw and root system decomposition. Recently, however, sugarcane producers are considering straw to be removed for electricity or second generation ethanol production. To elucidate the role of straw and root system on the carbon supply into the soil, the biomass inputs from sugarcane straw (tops and dry leaves) and from root system (rhizomes and roots) were quantified, and its contribution to provide C to the soil was estimated. Three trials were carried out in the State of Sao Paulo, Brazil, from 2006 to 2009. All sites were cultivated with the variety SP81 3250 under the green sugarcane harvest. Yearly, post-harvest sugarcane residues (tops, dry leaves, roots and rhizomes) were sampled; weighted and dried for the dry mass (DM) production to be estimated. On average, DM root system production was 4.6 Mg ha-1 year-1 (1.5 Mg C ha-1 year-1) and 11.5 Mg ha-1 year-1 (5.1 Mg C ha-1 year-1) of straw. In plant cane, 35 % of the total sugarcane DM was allocated into the root system, declining to 20 % in the third ratoon. The estimate of potential allocation of sugarcane residues to soil organic C was 1.1 t ha-1 year-1; out of which 33 % was from root system and 67 % from straw. The participation of root system should be higher if soil layer is evaluated, a deeper soil layer, if root exudates are accounted and if the period of higher production of roots is considered

Soil and crop residue CO2-C emission under tillage systems in sugarcane-producing areas of southern Brazil

Appropriate management of agricultural crop residues could result in increases on soil organic carbon (SOC) and help to mitigate gas effect. To distinguish the contributions of SOC and sugarcane (Saccharum spp.) residues to the short-term CO2-C loss, we studied the influence of several tillage systems: heavy offset disk harrow (HO), chisel plow (CP), rotary tiller (RT), and sugarcane mill tiller (SM) in 2008, and CP, RT, SM, moldboard (MP), and subsoiler (SUB) in 2009, with and without sugarcane residues relative to no-till (NT) in the sugarcane producing region of Brazil. Soil CO2-C emissions were measured daily for two weeks after tillage using portable soil respiration systems. Daily CO2-C emissions declined after tillage regardless of tillage system. In 2008, total CO2-C from SOC and/or residue decomposition was greater for RT and lowest for CP. In 2009, emission was greatest for MP and CP with residues, and smallest for NT. SOC and residue contributed 47 % and 41 %, respectively, to total CO2-C emissions. Regarding the estimated emissions from sugarcane residue and SOC decomposition within the measurement period, CO2-C factor was similar to sugarcane residue and soil organic carbon decomposition, depending on the tillage system applied. Our approach may define new emission factors that are associated to tillage operations on bare or sugarcane-residue-covered soils to estimate the total carbon loss