• Authors:
    • Paré, D.
    • Angers, D. A.
    • Laganière, J.
  • Source: Global Change Biology
  • Volume: 16
  • Issue: 1
  • Year: 2010
  • Summary: Deforestation usually results in significant losses of soil organic carbon (SOC). The rate and factors determining the recovery of this C pool with afforestation are still poorly understood. This paper provides a review of the influence of afforestation on SOC stocks based on a meta-analysis of 33 recent publications (totaling 120 sites and 189 observations), with the aim of determining the factors responsible for the restoration of SOC following afforestation. Based on a mixed linear model, the meta-analysis indicates that the main factors that contribute to restoring SOC stocks after afforestation are: previous land use, tree species planted, soil clay content, preplanting disturbance and, to a lesser extent, climatic zone. Specifically, this meta-analysis (1) indicates that the positive impact of afforestation on SOC stocks is more pronounced in cropland soils than in pastures or natural grasslands; (2) suggests that broadleaf tree species have a greater capacity to accumulate SOC than coniferous species; (3) underscores that afforestation using pine species does not result in a net loss of the whole soil-profile carbon stocks compared with initial values (agricultural soil) when the surface organic layer is included in the accounting; (4) demonstrates that clay-rich soils (>33%) have a greater capacity to accumulate SOC than soils with a lower clay content (<33%); (5) indicates that minimizing preplanting disturbances may increase the rate at which SOC stocks are replenished; and (6) suggests that afforestation carried out in the boreal climate zone results in small SOC losses compared with other climate zones, probably because trees grow more slowly under these conditions, although this does not rule out gains over time after the conversion. This study also highlights the importance of the methodological approach used when developing the sampling design, especially the inclusion of the organic layer in the accounting.
  • Authors:
    • Saggar, S.
    • de Klein, C. A. M.
    • Ledgard, S. F.
    • Luo, J.
  • Source: Agriculture, Ecosystems & Environment
  • Volume: 136
  • Issue: 3-4
  • Year: 2010
  • Summary: Nitrous oxide (N2O) emissions from grazed pastures represent a significant source of atmospheric N2O. With an improved understanding and quantification of N sources, transformation processes, and soil and climatic conditions controlling N2O emissions, a number of management options can be identified to reduce N2O emissions from grazed pasture systems. The mitigation options discussed in this paper are: optimum soil management, limiting the amount of N fertiliser or effluent applied when soil is wet; lowering the amount of N excreted in animal urine by using low-N feed supplements as an alternative to fertiliser N-boosted grass; plant and animal selection for increased N use efficiency, using N process inhibitors that inhibit the conversion of urea to ammonium and ammonium to nitrate in soil; use of stand-off/feed pads or housing systems during high risk periods of N loss. The use of single or multiple mitigation options always needs to be evaluated in a whole farm system context and account for total greenhouse gas emissions including methane and carbon dioxide. They should focus on ensuring overall efficiency gains through decreasing N losses per unit of animal production and achieving a tighter N cycle. Whole-system life-cycle-based environmental analysis should also be conducted to assess overall environmental emissions associated the N2O mitigation options. (C) 2009 Elsevier B.V. All rights reserved.
  • Authors:
    • Sun, O. J.
    • Wang, E. L.
    • Luo, Z. K.
  • Source: Geoderma
  • Volume: 155
  • Issue: 3-4
  • Year: 2010
  • Summary: Soil is the largest reservoir of carbon (C) in the terrestrial biosphere and a slight variation in this pool could lead to Substantial changes in the atmospheric CO2 concentration, thus impact significantly on the global climate. Cultivation of natural ecosystems has led to marked decline in soil C storage, such that conservation agricultural practices (CAPs) are widely recommended as options to increase soil C storage, thereby mitigating climate change. In this review, we summarise soil C change as a result of cultivation worldwide and in Australia. We then combine the available data to examine the effects of adopting CAPs on soil C dynamics in Australian agro-ecosystems. Finally, we discuss the future research priorities related to soil C dynamics. The available data show that in Australian agro-ecosystems, cultivation has led to C loss for more than 40 years, with a total C loss of approximately 51% in the surface 0.1 m of soil. Adoption of CAPs generally increased soil C. Introducing perennial plants into rotation had the greatest potential to increase soil C by 18% compared with other CAPs. However, the same CAPS Could result in different outcomes on soil C under different climate and soil combinations. No consistent trend of increase in soil C was found with the duration of CAP applications, implying that questions remain regarding long-term impact of CAPs. Most of the available data in Australia are limited to the surface 0.1 to 0.3 m of soil. Efforts are needed to investigate soil C change in deeper soil layers in Order to understand the impact of crop root growth and various agricultural practices on C distribution in soil profile. Elevated atmospheric CO2 concentration, global warming and rainfall change Could all alter the C balance of agricultural soils. Because of the complexity of soil C response to management and environmental factors, a system modelling approach Supported by sound experimental data would provide the most effective means to analyse the impact of different management practices and future climate change on soil C dynamics. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.
  • Authors:
    • Sun, O. J.
    • Wang, E.
    • Luo, Z.
  • Source: Agriculture, Ecosystems & Environment
  • Volume: 139
  • Issue: 1-2
  • Year: 2010
  • Summary: Adopting no-tillage in agro-ecosystems has been widely recommended as a means of enhancing carbon (C) sequestration in soils. However, study results are inconsistent and varying from significant increase to significant decrease. It is unclear whether this variability is caused by environmental, or management factors or by sampling errors and analysis methodology. Using meta-analysis, we assessed the response of soil organic carbon (SOC) to conversion of management practice from conventional tillage (CT) to no-tillage (NT) based on global data from 69 paired-experiments, where soil sampling extended deeper than 40 cm. We found that cultivation of natural soils for more than 5 years, on average, resulted in soil C loss of more than 20 t ha-1, with no significant difference between CT and NT. Conversion from CT to NT changed distribution of C in the soil profile significantly, but did not increase the total SOC except in double cropping systems. After adopting NT, soil C increased by 3.15 +- 2.42 t ha-1 (mean ± 95% confidence interval) in the surface 10 cm of soil, but declined by 3.30 ± 1.61 t ha-1 in the 20-40 cm soil layer. Overall, adopting NT did not enhance soil total C stock down to 40 cm. Increased number of crop species in rotation resulted in less C accumulation in the surface soil and greater C loss in deeper layer. Increased crop frequency seemed to have the opposite effect and significantly increased soil C by 11% in the 0-60 cm soil. Neither mean annual temperature and mean annual rainfall nor nitrogen fertilization and duration of adopting NT affected the response of soil C stock to the adoption of NT. Our results highlight that the role of adopting NT in sequestrating C is greatly regulated by cropping systems. Increasing cropping frequency might be a more efficient strategy to sequester C in agro-ecosystems. More information on the effects of increasing crop species and frequency on soil C input and decomposition processes is needed to further our understanding on the potential ability of C sequestration in agricultural soils.
  • Authors:
    • Rosegrant, M.
    • Derner, J. D.
    • Schuman, G. E.
    • Verchot, L.
    • Steinfeld, H.
    • Gerber, P.
    • De Freitas, P. L.
    • Lal, R.
    • Desjardins, R. L.
    • Dumanski, J.
  • Source: Applied Agrometeorology
  • Year: 2010
  • Summary: Agriculture can make significant contributions to climate change mitigation by (a) increasing soil organic carbon (SOC) sinks, (b) reducing GHG emissions, and (c) off-setting fossil fuel by promoting biofuels. The latter has the potential to counter-balance fossil fuel emissions to some degree, but the overall impact is still uncertain compared to emissions of non-CO2 GHGs, which are likely to increase as production systems intensify. Agricultural lands also remove CH4 from the atmosphere by oxidation, though less than forestlands (Tate et al. 2006; Verchot et al. 2000), but this effect is small compared to other GHG fluxes (Smith and Conen 2004).
  • Authors:
    • Andrasko, K.
    • Bosquet, B.
  • Year: 2010
  • Authors:
    • Dalal, R. C.
    • Page, K. L.
    • Pringle, M. J.
    • Allen, D. E.
  • Source: The Rangeland Journal
  • Volume: 32
  • Issue: 2
  • Year: 2010
  • Summary: The accurate measurement of the soil organic carbon (SOC) stock in Australian grazing lands is important due to the major role that SOC plays in soil productivity and the potential influence of soil C cycling on Australia's greenhouse gas emissions. However, the current sampling methodologies for SOC stock are varied and potentially conflicting. It was the objective of this paper to review the nature of, and reasons for, SOC variability; the sampling methodologies commonly used; and to identify knowledge gaps for SOC measurement in grazing lands. Soil C consists of a range of biological materials, in various SOC pools such as dissolved organic C, micro- and meso-fauna (microbial biomass), fungal hyphae and fresh plant residues in or on the soil (particulate organic C, light-fraction C), the products of decomposition (humus, slow pool C) and complexed organic C, and char and phytoliths (inert, passive or resistant C); and soil inorganic C (carbonates and bicarbonates). Microbial biomass and particulate or light-fraction organic C are most sensitive to management or land-use change; resistant organic C and soil carbonates are least sensitive. The SOC present at any location is influenced by a series of complex interactions between plant growth, climate, soil type or parent material, topography and site management. Because of this, SOC stock and SOC pools are highly variable on both spatial and temporal scales. This creates a challenge for efficient sampling. Sampling methods are predominantly based on design-based (classical) statistical techniques, crucial to which is a randomised sampling pattern that negates bias. Alternatively a model-based (geostatistical) analysis can be used, which does not require randomisation. Each approach is equally valid to characterise SOC in the rangelands. However, given that SOC reporting in the rangelands will almost certainly rely on average values for some aggregated scale (such as a paddock or property), we contend that the design-based approach might be preferred. We also challenge soil surveyors and their sponsors to realise that: (i) paired sites are the most efficient way of detecting a temporal change in SOC stock, but destructive sampling and cumulative measurement errors decrease our ability to detect change; (ii) due to (i), an efficient sampling scheme to estimate baseline status is not likely to be an efficient sampling scheme to estimate temporal change; (iii) samples should be collected as widely as possible within the area of interest; (iv) replicate of laboratory analyses is a critical step in being able to characterise temporal change. Sampling requirements for SOC stock in Australian grazing lands are yet to be explicitly quantified and an examination of a range of these ecosystems is required in order to assess the sampling densities and techniques necessary to detect specified changes in SOC stock and SOC pools. An examination of techniques that can help reduce sampling requirements (such as measurement of the SOC fractions that are most sensitive to management changes and/or measurement at specific times of the year, preferably before rapid plant growth, to decrease temporal variability), and new technologies for in situ SOC measurement is also required.
  • Authors:
    • Reid, R.
  • Source: Plant Science
  • Volume: 178
  • Issue: 1
  • Year: 2010
  • Summary: High boron concentrations in soil and in irrigation water reduce crop productivity in many areas of the world. Plant tolerance to boron toxicity has been identified in a range of genotypes and recent research has revealed a physiological mechanism behind this tolerance in cereals. Cultivars with high levels of expression of a gene encoding a boron-efflux transporter in roots and shoots have been reported to show tolerance to high boron in soils and in solution culture experiments conducted under controlled conditions in glasshouses and growth rooms. However, field trials of tolerant cultivars in rain-fed semi-arid environments have been disappointing with few showing even modest improvements in yield, and others showing either no effect or a decrease in yields.
  • Authors:
    • Chen, C.
    • Xu, Z.
    • Wu, H.
    • Zhou, X.
  • Source: Proceedings of the 19th World Congress of Soil Science: Soil solutions for a changing world, Brisbane, Australia, 1-6 August 2010. Working Group 3.5 Paddy soils and water scarcity
  • Year: 2010
  • Summary: Winter cover crops are not only one of effective agricultural management practices to control weeds but also can improve soil fertility, resulting in increasing crop productions. Up to now, however, little is known about information on how much of soil soluble organic carbon (C) incorporates into the soils applied with winter cover crops, which is a prerequisite to design strategies that improve C sequestration in agricultural ecosystems. The aims of this study were to: (1) assess the effects of winter cover crops on soluble organic carbon (SOC) pools using different extraction methods (KCl extractable organic C; microbial biomass) and microbial community functional diversity, and (2) quantify how much of the potentially mineralizable organic C pools (C 0) incorporates into the soils and associated half-life of SOC remaining under seven cover crops and nil-crop control (CK) in temperate agricultural soils of southern Australia. Cover crop treatments are cereal rye, wheat, saia oats, vetch, field peas, mustard and the mixture of cereal rye and vetch. Results showed that the CK treatment had higher soil moisture content and lower soluble organic nitrogen (SON) compared to the cover crop treatments. Among the cover crop treatments, there was significantly higher SON in the wheat, oats and vetch treatments than in the other treatments. The oats treatment had the highest amount of cumulative CO 2-C than any other treatments over one-month incubation experiment. An exponential regression approach for C mineralization was used to estimate C o and soil samples under the cover crops can be divided into four groups depending on C o. The principal component analysis of the MicroResp TM profiles showed that the CK treatment was significantly different from the cover crop treatments. The cover crop treatments with wheat, vetch and peas as well as mustard form a cluster which was significantly different from the other clusters. In addition, the vetch, field peas and mustard treatments showed higher Shannon diversity H and Evenness (E) and Simpson diversity H compared to the other cover crop treatments with the lowest Shannon H and E at CK. In conclusion, overall, the vetch and field peas as well as wheat winter cover crop may be better management practices for agricultural ecosystems in southern Australia.
  • Authors:
    • Andrew, J.
    • Gazey, C.
  • Source: Proceedings of the 19th World Congress of Soil Science: Soil solutions for a changing world, Brisbane, Australia, 1-6 August 2010. Symposium 4.1.2 Management and protection of receiving environments
  • Year: 2010
  • Summary: Surface application of agricultural lime to treat acidity in the soil profile delivers multiple benefits to the broadcare dryland farming systems in Western Australia. Soil pH measured in 2009 to a depth of 40-50 cm was increased by applications of lime applied in 1991 and 2000. The ameliorated soil pH profile, which meets the Wheatbelt Natural Resource Management 2025 resource targets (Avon Catchment Council 2005) (designed to remove acidity as a constraint to productive agriculture), has provided multiple benefits in terms of increased productivity, increased crop competitiveness, reduced weed burden, reduced risk of soil erosion by wind due to increased biomass cover and potentially reduced off-site effects which result from decreased water use efficiency on profiles with low pH. Current annual losses due to soil acidity for the WA wheatbelt are estimated at between $300-400 million or around 9% of the total crop. The treated soil profile in this trial returned $175/ha benefit from increased wheat yield in 2008 and $225/ha benefit from increased barley grain yield in 2009.