• Authors:
    • Muirhead, B.
    • Nelson, P. N.
    • Bass, A. M.
    • Agegnehu, G.
    • Wright,Graeme
    • Bird,Michael I.
  • Source: Article
  • Volume: 213
  • Year: 2015
  • Summary: This study investigated the effects of biochar and compost, applied individually or together, on soil fertility, peanut yield and greenhouse gas (GHG) emissions on a Ferralsol in north Queensland, Australia. The treatments were (1) inorganic fertilizer only (F) as a control; (2) 10 t ha(-1) biochar + F (B +F); (3) 25 t compost +F (Com +F) ha-1; (4) 2.5t B ha(-1) + 25 t Com ha-1 mixed on site +F; and (5) 25 t ha(-1) cocomposted biochar-compost + F (COMBI + F). Application of B and COMBI increased seed yield by 23% and 24%, respectively. Biochar, compost and their mixtures significantly improved plant nutrient availability and use, which appeared critical in improving peanut performance. Soil organic carbon (SOC) increased from 0.93% (F only) to 1.25% (B amended), soil water content (SWC) from 18% (F only) to over 23% (B amended) and CEC from 8.9 cmol(+)/kg (F only) to over 103 cmol(+)/kg (organic amended). Peanut yield was significantly positively correlated with leaf chlorophyll content, nodulation number (NN), leaf nutrient concentration, SOC and SWC for the organic amendments. Fluxes of CO2 were highest for the F treatment and lowest for the COMBI treatment, whereas N2O flux was highest for the F treatment and all organic amended plots reduced N2O flux relative to the control. Principal component analysis indicates that 24 out of 30 characters in the first principal component (PRIN1) individually contributed substantial effects to the total variation between the treatments. Our study concludes that applications of B, Cam, B +Com or COMBI have strong potential to, over time, improve SOC, SWC, soil nutrient status, peanut yield and abate GHG fluxes on tropical Ferralsols. Crown Copyright (C) 2015 Published by Elsevier B.V. All rights reserved.
  • Authors:
    • Pritchard, D.
    • Biswas, W.
    • Engelbrecht, D.
    • Ahmad, W.
  • Source: Remote Sensing Applications: Society and Environment
  • Volume: 2
  • Year: 2015
  • Summary: The causes and implications of climate change are currently at the forefront of many researching agendas. Countries that have ratified the Kyoto Protocol are bound by agreements to focus on and reduce greenhouse gas emissions which impact on the natural and anthropogenic environment. Internationally agriculture contributes to environmental impacts such as land use change, loss of biodiversity, greenhouse gas emissions, increased soil salinity, soil acidity and soil erosion. To combat and control the greenhouse gas emissions generated during agricultural production, methodologies are being developed and investigated worldwide. Agriculture is the second largest emitter of greenhouse gases in Australia and consequently the integrated spatial technology was developed using data from a crop rotation project conducted by the Department of Agriculture and Food, Western Australia. The aim of the integrated spatial technology was to combine remote sensing, geographical information systems and life cycle assessment, to ascertain the component or system within the agricultural production cycle, generating the most greenhouse gases. Cleaner production strategies were then used to develop mitigation measures for the reduction of greenhouse gases within the integrated spatial technology. © 2015 Elsevier B.V.
  • Authors:
    • Howden, M.
    • Chapman, S.
    • Zheng, B.
    • Moore, A.
    • Kokic, P.
    • Ghahramani, A.
    • Crimp, S.
  • Source: Agriculture, Ecosystems & Environment
  • Volume: 211
  • Issue: December 2015
  • Year: 2015
  • Summary: Wheat is one of the main grains produced across the globe and wheat yields are sensitive to changes in climate. Australia is a major exporter of wheat, and variations in its national production influence trade supplies and global markets. We evaluated the effect of climate change in 2030 compared to a baseline period (1980-1999) by upscaling from farm to the national level. Wheat yields and gross margins under current and projected climates were assessed using current technology and management practices and then compared with 'best adapted' yield achieved by adjustments to planting date, nitrogen fertilizer, and available cultivars for each region. For the baseline climate (1980-1999), there was a potential yield gap modelled as optimized adaptation gave potential up scaled yields (tonne/ha) and gross margins (AUD$/ha) of 17% and 33% above the baseline, respectively. In 2030 and at Australian wheatbelt level, climate change impact projected to decline wheat yield by 1%. For 2030, national wheat yields were simulated to decrease yields by 1% when using existing technology and practices but increase them by 18% assuming optimal adaptation. Hence, nationally at 2030 for a fully-adapted wheat system, yield increased by 1% and gross margin by 0.3% compared to the fully adapted current climate baseline. However, there was substantial regional variation with median yields and gross margins decreasing in 55% of sites. Full adaptation of farm systems under current climate is not expected, and so this will remain an on-going challenge. However, by 2030 there will be a greater opportunity to increase the overall water use and nitrogen efficiencies of the Australian wheat belt, mostly resulting from elevated atmospheric CO 2 concentrations.
  • Authors:
    • Flower, K.
    • Manalil, S.
  • Source: SOIL & TILLAGE RESEARCH
  • Volume: 143
  • Issue: 123-129
  • Year: 2014
  • Summary: Interest in fallowing as the drought adaptation strategy has increased recently due to the occurrence of frequent droughts in cropping areas of Australia. Weed management in a fallow is crucial as it affects the level of soil water and nitrogen conserved by this practice. Increased use of fallow has implications for nitrous oxide emissions as soil moisture is a major determinant of evolution of nitrous oxide. In a two year study, three types of fallow with different weed management were compared with wheat and canola crops in 2010 and the carry-over effects with wheat on all plots in 2011. The weeds in the fallows were managed either by herbicide (chemical fallow) or by tillage (cultivation fallow) and compared to an unweeded fallow (weedy fallow). The chemical fallow conserved most soil water followed by cultivation fallow, with the lowest soil water content in the weedy fallow. In addition, more weeds were observed in the wheat crop following weedy fallow. Low wheat and canola yields were measured in 2010 because of a drought, which also depleted soil water compared to the chemical and cultivation fallows. Therefore, fallow is a potential strategy for increasing crop yield under dry conditions. The results also indicated that weeds had a detrimental effect by reducing soil water content due to lack of timely weed management. To test the compatibility of fallow with climate-change mitigation, the nitrous oxide emissions were compared in the 2011 wheat crop. There was a temporal fluctuation in nitrous oxide emissions with increased rates of emission after top dressing with urea. Importantly, however, the nitrous oxide emission from wheat following fallow was not increased compared with wheat in the continuous cropping sequences. Therefore, this study found that fallowing with good weed control, could be used as a drought adaptation strategy without increasing nitrous oxide emissions in following crops.
  • Authors:
    • Stokes, C. J.
    • Marshall, N.
  • Source: CLIMATIC CHANGE
  • Volume: 126
  • Issue: 3-4
  • Year: 2014
  • Summary: Primary producers, including graziers, crop farmers and commercial fishers are especially vulnerable to climate change because they depend on highly climate-sensitive natural resources. Adaptation to climate change will make a major difference to the severity of the impacts experienced. However, individuals (resource users) can erect sometimes seemingly peculiar barriers to potential adaptation options that need to be addressed if adaptation is to be effective. Our aim was to understand the nature of barriers to change for cattle graziers in the northern Australian rangelands. We conceptualised barriers as adverse reactions where resource users are unlikely to contemplate adaptations that threaten core values or perceptions about themselves. We assumed that resource users that were more sensitive to climate change impacts-or more dependent on the resource-were more proximate to thresholds of coping and thus more likely to erect barriers, especially people with little adaptive capacity. Given that climate sensitivity and adaptive capacity are important components of vulnerability, our approach was to conduct a vulnerability assessment to identify potential but important barriers to change. Data from 240 graziers suggest that graziers in northern Australia might be especially vulnerable to climate change because their identity, place attachment, low employability, weak networks and dependents can make them sensitive to change, and their sensitivity can be compounded by a low adaptive capacity. We argue that greater attention needs to be placed on the social context of climate change impacts and on the processes shaping vulnerability and adaptation, especially at the scale of the individual.
  • Authors:
    • Wuest, S.
  • Source: SOIL SCIENCE SOCIETY OF AMERICA JOURNAL
  • Volume: 78
  • Issue: 4
  • Year: 2014
  • Summary: Long-term changes in total soil organic C usually occur gradually. These long-term trends might be obscured by smaller, rapid changes in soil C due to seasonal inputs of plant residues, roots, and exudates, or decomposition of such inputs. Yet there is little, if any, data describing the magnitude of seasonal changes in soil C. If seasonal fluctuations in soil C are substantial, then important implications exist for accurate comparison of soil C between sites, between treatments, and even in the same experimental unit over time. Thirty-nine consecutive monthly soil samples were taken from a field experiment planted every year with winter wheat (Triticum aestivum L.) in the Pacific Northwest, United States. The variation in soil organic C was 14 to 16% of the mean over the 39-mo period in the top 250 kg m-2 equivalent mass (~0- to 20-cm depth). Two to eight percent could be identified as a regular seasonal pattern. The no-till management system had the greatest seasonal fluctuation, and the timing of the annual maximum was different from that of the tilled soil management treatments. In the shallower soil layer (~0-7 cm), total soil organic C varied 12 to 29% in which 4 to 13% could be attributed to a 12-mo seasonal pattern. Given the small magnitude of changes in soil C being measured and modeled in many agricultural and natural systems, soil samples taken at a single point in time are likely to encounter substantial but hidden measurement variability. The variability may be compounded by factors of the timing of sampling in relation to natural soil organic matter cycles and differences in the cycle due to treatment and weather. Sampling plans, which account for seasonal fluctuation and the different fluctuation patterns under different soil situations, will improve measurement accuracy.
  • Authors:
    • Herridge, D.
    • Guppy, C.
    • Begum, N.
    • Schwenke, G.
  • Source: Biology and Fertility of Soils
  • Volume: 50
  • Issue: 3
  • Year: 2014
  • Summary: Few studies have compared emissions of nitrous oxide (N2O), the potent greenhouse gas associated with decomposition of both below-ground (root) and above-ground (shoot) residues. We report a laboratory incubation experiment to evaluate effects of root and shoot residues from wheat, canola, soybean, and sorghum, incorporated into a naturally fertile acidic Black Vertisol, on N2O and carbon dioxide (CO2) emissions. The residue-amended Vertisol samples were incubated at 25 A degrees C and 70 % water-filled pore space (WFPS) to facilitate denitrification activity for a total period of 56 days. The incubated soils were periodically sampled for N2O, CO2, mineral N, and dissolved organic carbon (DOC). In general, shoot residues emitted more CO2 than roots, while N2O emissions were 50-70 % higher in cereal root residues than those in shoots. Surprisingly, the highest N2O emissions were associated with soils amended with the more inert high C/N ratio residues (wheat and sorghum roots), and to some extent, lowest emissions were associated with low C/N ratio (more labile) residues, particularly during the early stages of incubation (0-22 days). During this stage, there was a significant (p < 0.01) and negative correlation between N2O emissions and microbial respiration (CO2 efflux) and a positive (p < 0.001) correlation between microbial respiration and DOC. These results suggest that residue decomposition linked to N immobilization reduced N2O emissions during this early stage. Only, later in the study (23-56 days), did the high %N, low C/N ratio residues of soybean shoot and canola roots release at least twice as much N2O as the majority of the other treatments. We concluded that the unexpected patterns of N2O emissions were a result of the initially high mineral N content of the incubated soils and that root residues are likely to contribute substantially to emissions from cropping soils.
  • Authors:
    • Rebetzke, G. J.
    • Watt, M.
    • Kirkby, C. A.
    • Hunt, J. R.
    • Conyers, M. K.
    • Kirkegaard, J. A.
  • Source: Agriculture, Ecosystems & Environment
  • Volume: 187
  • Issue: April
  • Year: 2014
  • Summary: Adoption of conservation agriculture (CA) principles in Australia increased rapidly during the 1990s and it now boasts the highest adoption rates worldwide. These principles of (1) diverse rotations (2) reduced (or no-) till systems and (3) the maintenance of surface cover make good sense in extensive, mechanised, rain-fed cropping systems on erosion-prone, structurally-unstable soils. Indeed reduced fuel and labour costs, soil conservation and moisture retention are the most commonly stated reasons for adoption of CA principles by farmers in Australia. Yet even in Australia, while broadly applicable, the adaptation and application of CA principles within specific farming systems remains pragmatic due to the diverse biophysical and socio-economic factors encountered. Most "no-till" adopters continue some strategic tillage (similar to 30% cropped area) for a range of sound agronomic reasons, intensive cereal systems dominate, and partial removal of crop residues as hay or by grazing livestock is commonplace within the largely mixed-farming systems. Although this challenges the notion of "ideal" CA principles (zero-till with no soil disturbance, full stubble retention and >3 species in rotations) this high degree of flexibility in CA principles as practiced in southern Australian mixed farming systems makes sense to optimize both economic and environmental outcomes. In addition, some proposed ecosystem service benefits of CA such as soil carbon sequestration and energy efficiency have been recently questioned. Though the socio-economic factors of small-holder farming systems in Africa and south Asia are more diverse and clearly different to Australian farms, some of the biophysical challenges and economic realities are shared (infertile soils, variable and extreme climates, relatively low input levels, integrated crop-livestock systems, small profit margins, highly variable income). It is therefore useful to consider from a biophysical standpoint why a pragmatic approach to CA principles has been necessary, even in a relatively high-adopting country like Australia, and why we should expect similarly 'imperfect' adoption of CA (if at all) in the diverse smallholder systems of Sub-Saharan Africa and South Asia. We review aspects of CA adoption in Australia in an effort to draw out important lessons as CA principles are adapted elsewhere, including the smallholder farming systems of Sub-Saharan Africa and South Asia. (C) 2013 Elsevier B.V. All rights reserved.
  • Authors:
    • McGree, J.
    • Bell, M.
    • Rowlings, D.
    • Grace, P.
    • Scheer, C.
    • Migliorati, M.
  • Source: Agriculture, Ecosystems & Environment
  • Volume: 186
  • Year: 2014
  • Summary: Global cereal production will need to increase by 50% to 70% to feed a world population of about 9 billion by 2050. This intensification is forecast to occur mostly in subtropical regions, where warm and humid conditions can promote high N2O losses from cropped soils. To secure high crop production without exacerbating N20 emissions, new nitrogen (N) fertiliser management strategies are necessary. This one-year study evaluated the efficacy of a nitrification inhibitor (3,4-dimethylpyrazole phosphate DMPP) and different N fertiliser rates to reduce N2O emissions in a wheat-maize rotation in subtropical Australia. Annual N2O emissions were monitored using a fully automated greenhouse gas measuring system. Four treatments were fertilized with different rates of urea, including a control (40 kg-N ha(-1) year(-1)), a conventional N fertiliser rate adjusted on estimated residual soil N (120 kg-N ha-1 year-1), a conventional N fertiliser rate (240 kg-N ha-1 year-1) and a conventional N fertiliser rate (240 kg-N ha-1 year-1) with nitrification inhibitor (DMPP) applied at top dressing. The maize season was by far the main contributor to annual N2O emissions due to the high soil moisture and temperature conditions, as well as the elevated N rates applied. Annual N2O emissions in the four treatments aMounted to 0.49, 0.84, 2.02 and 0.74 kg N2O N ha-1 year-1, respectively, and corresponded to emission factors of 0.29%, 0.39%, 0.69% and 0.16% of total N applied. Halving the annual conventional N fertiliser rate in the adjusted N treatment led to N2O emissions comparable to the DMPP treatment but extensively penalised maize yield. The application of DMPP produced a significant reduction in N2O emissions only in the maize season. The use of DMPP with urea at the conventional N rate reduced annual N2O emissions by more than 60% but did not affect crop yields. The results of this study indicate that: (i) future strategies aimed at securing subtropical cereal production without increasing N2O emissions should focus on the fertilisation of the summer crop; (ii) adjusting conventional N fertiliser rates on estimated residual soil N is an effective practice to reduce N2O emissions but can lead to substantial yield losses if the residual soil N is not assessed correctly; (iii) the application of DMPP is a feasible strategy to reduce annual N2O emissions from sub-tropical wheat-maize rotations. However, at the N rates tested in this study DMPP urea did not increase crop yields, making it impossible to recoup extra costs associated with this fertiliser. The findings of this study will support farmers and policy makers to define effective fertilisation strategies to reduce N2O emissions from subtropical cereal cropping systems while maintaining high crop productivity. More research is needed to assess the use of DMPP urea in terms of reducing conventional N fertiliser rates and subsequently enable a decrease of fertilisation costs and a further abatement of fertiliser-induced N2O emissions. (c) 2014 Elsevier B.V. All rights reserved.
  • Authors:
    • Farquharson, R.
    • Cressie, N.
    • Baldock, J.
    • Pagendam, D.
    • Clifford, D.
    • Farrell, M.
    • Macdonald, L.
    • Murray, L.
  • Source: Environmetrics
  • Volume: 25
  • Issue: 4
  • Year: 2014
  • Summary: The benefits of sequestering carbon are many, including improved crop productivity, reductions in greenhouse gases, and financial gains through the sale of carbon credits. Achieving better understanding of the sequestration process has motivated many deterministic models of soil carbon dynamics, but none of these models address uncertainty in a comprehensive manner. Uncertainty arises in many ways - around the model inputs, parameters, and dynamics, and subsequently model predictions. In this paper, these uncertainties are addressed in concert by incorporating a physical-statistical model for carbon dynamics within a Bayesian hierarchical modelling framework. This comprehensive approach to accounting for uncertainty in soil carbon modelling has not been attempted previously. This paper demonstrates proof-of-concept based on a one-pool model and identifies requirements for extension to multi-pool carbon modelling. Our model is based on the soil carbon dynamics in Tarlee, South Australia. We specify the model conditionally through its parameters, soil carbon input and decay processes and observations of those processes. We use a particle marginal Metropolis-Hastings approach specified using the LibBi modelling language. We highlight how samples from the posterior distribution can be used to summarise our knowledge about model parameters, to estimate the probabilities of sequestering carbon and to forecast changes in carbon stocks under crop rotations not represented explicitly in the original field trials.