• 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:
    • Peth, S.
    • Mordhorst, A.
    • Horn, R.
  • Source: Geoderma
  • Volume: 219
  • Issue: May
  • Year: 2014
  • Summary: Mechanical disturbance of soil structure is commonly related to altered physical changes in pore systems, which control CO2 effluxes e.g. by changes in gas transport properties and in microbial activity. Soil compaction mostly leads to reduced CO2 fluxes. In contrast, structured soils can also release physically entrapped CO2 or give access to protected carbon sources inside aggregates due to aggregate breakdown by disruptive forces. In this study it was investigated how far arable soil management affects structure- and compaction-related CO2-releases using incubation experiments and CO2 gas analysis under standard matric potentials (-6 kPa). CO2 efflux was analyzed before, during and after mechanical loading using the alkali trap method (static efflux) and a gas flow compaction device (GaFloCoD, dynamic efflux). Intact soil cores (236 and 471 cm(3)) were collected from a Stagnic Luvisol with loamy sand (conservation and conventional tillage systems) and a Haplic Luvisol with clayey silt (under different fodder crops) from the topsoil (10-15 cm) and subsoil (35-45 cm). Mechanical stability was reflected by the pre-compression stress value (P-c) and by the tensile strength of aggregates (12-20 mm). Changes in pore systems were described by air conductivity as well as air capacity and total porosity. While CO2-releases varied highly during the compaction process (GaFloCoD) for different stress magnitudes, soil depths and management systems, basal respiration rates were generally reduced after mechanical loading by almost half of the initial rates irrespective of soil management. For both methods (dynamic and static efflux) restriction in gas transport functionality was proved to have major influence on inhibition of CO2 efflux due to mechanical loading. GaFloCoD experiments demonstrated that decreases in CO2 efflux were linked to structural degradation of pore systems by exceeding internal soil strength (P-c). Otherwise, re-equilibrating matric potentials to 6 kPa and re-incubating offset inhibition of soil respiration suggest a re-enhancement of microbial activity. At this state, physical influences were apparently overlapped by biological effects due to higher energy supply to microbes, which could be offered by spatial distribution changes of microorganisms and organic substrates within a given soil structure. This implies the susceptibility of physical protection mechanism for carbon by disruption of soil structure. In future, special focus should be given on a clear distinction between physical and microbiological effects controlling CO2 fluxes in structured soils. (C) 2014 Elsevier B.V. All rights reserved.
  • Authors:
    • Braden, J. B.
    • Cai, X.
    • Eheart, J. W.
    • Ng, T. L.
    • Czapar, G. F.
  • Source: Journal of Water Resources Planning and Management
  • Volume: 140
  • Issue: 1
  • Year: 2014
  • Summary: Excessive nitrate loads in surface waters are a major cause of hypoxia and eutrophication. In many places, agriculture is the single largest source of nitrogen entering receiving waters. Perennial energy grass crops have the potential to reduce nitrogen loads from agricultural areas, while sequestering carbon and offering new economic opportunities for farmers. This study analyzes farm system-scale cropping and fertilizer application decisions, and resulting nitrate loads, as driven by prices for the bioenergy crop miscanthus, as well as investigates reductions of carbon and other greenhouse gas emissions and nitrogen fertilizer use. An economic model of farm-system-scale decisions is coupled to a hydrologic-agronomic model of the physical stream system to obtain nitrate loading and crop yield results for varying combinations of prices and policies for a typical Midwestern agricultural watershed. For the scenarios examined, a large reduction in stream nitrate load depends on a high price for miscanthus relative to competing crops. A price for miscanthus that exceeds 50% of the average of corn and soybean prices, per unit weight, is estimated to lead to nitrate load reductions of 25% or more. Though significant, these reductions are still less than the recommended 45% reduction in stream nitrogen flux entering the Gulf of Mexico needed to mitigate the hypoxia problem in the gulf. Miscanthus prices are unlikely ever to reach such levels. However, nitrate load reductions could still be achieved by implementing a nitrogen fertilizer reduction subsidy alongside a miscanthus market. The results also show that carbon trading is unlikely to result in any significant reduction in nitrate load. The results are useful for improving understanding of the potential of these incentives, individually and concurrently, to reduce pollution from Midwestern crop agriculture.
  • Authors:
    • Gatere, L.
    • DeClerck, F.
    • Blanco-Canqui, H.
    • Palm, C.
    • Grace, P.
  • Source: Agriculture, Ecosystems & Environment
  • Volume: 187
  • Issue: April
  • Year: 2014
  • Summary: Conservation agriculture (CA) changes soil properties and processes compared to conventional agriculture. These changes can, in turn, affect the delivery of ecosystem services, including climate regulation through carbon sequestration and greenhouse gas emissions, and regulation and provision of water through soil physical, chemical and biological properties. Conservation agriculture can also affect the underlying biodiversity that supports many ecosystem services. In this overview, we summarize the current status of the science, the gaps in understanding, and highlight some research priorities for ecosystem services in conservational agriculture. The review is based on global literature but also addresses the potential and limitations of conservation agriculture for low productivity, smallholder farming systems, particularly in Sub Saharan Africa and South Asia. There is clear evidence that topsoil organic matter increases with conservation agriculture and with it other soil properties and processes that reduce erosion and runoff and increase water quality. The impacts on other ecosystem services are less clear. Only about half the 100+ studies comparing soil carbon sequestration with no-till and conventional tillage indicated increased sequestration with no till; this is despite continued claims that conservation agriculture sequesters soil carbon. The same can be said for other ecosystem services. Some studies report higher greenhouse gas emissions (nitrous oxide and methane) with conservation agriculture compared to conventional, while others find lower emissions. Soil moisture retention can be higher with conservation agriculture, resulting in higher and more stable yields during dry seasons but the amounts of residues and soil organic matter levels required to attain higher soil moisture content is not known. Biodiversity is higher in CA compared to conventional practices. In general, this higher diversity can be related to increased ecosystem services such as pest control or pollination but strong evidence of cause and effect or good estimates of magnitude of impact are few and these effects are not consistent. The delivery of ecosystem services with conservation agriculture will vary with the climate, soils and crop rotations but there is insufficient information to support a predictive understanding of where conservation agriculture results in better delivery of ecosystem services compared to conventional practices. Establishing a set of strategically located experimental sites that compare CA with conventional agriculture on a range of soil-climate types would facilitate establishing a predictive understanding of the relative controls of different factors (soil, climate, and management) on ES outcomes, and ultimately in assessing the feasibility of CA or CA practices in different sites and socioeconomic situations. The feasibility of conservation agriculture for recuperating degraded soils and increasing crop yields on low productivity, smallholder farming systems in the tropics and subtropics is discussed. It is clear that the biggest obstacle to improving soils and other ES through conservation agriculture in these situations is the lack of residues produced and the competition for alternate, higher value use of residues. This limitation, as well as others, point to a phased approach to promoting conservation agriculture in these regions and careful consideration of the feasibility of conservation agriculture based on evidence in different agroecological and socioeconomic conditions.
  • Authors:
    • Alvaro-Fuentes, J.
    • Cantero-Martinez, C.
    • Plaza-Bonilla, D.
  • Source: Soil Biology and Biochemistry
  • Volume: 68
  • Year: 2014
  • Summary: Agricultural management practices play an important role in greenhouse gases (GHG) emissions due to their impact on the soil microenvironment. In this study, two experiments were performed to investigate the influence of tillage and N fertilization on GHG production at the macroaggregate scale. In the first experiment, soil macroaggregates collected from a field experiment comparing various soil management systems (CT, conventional tillage; NT, no-tillage) and N fertilization types (a control treatment without N and mineral N and organic N with pig slurry treatments both at 150 kg N ha-(1)) were incubated for 35 days. Methane (CH4), carbon dioxide (CO2) and nitrous oxide (N2O) production was quantified at regular time intervals by gas chromatography. In the second experiment, the effects of fertilization type and soil moisture on the relative importance of nitrification and denitrification processes in N2O emission from soil macroaggregates were quantified. Nitrate ammonium, macroaggregate-C concentration, macroaggregate water-stability, microbial biomass-C and N (MBC and MBN, respectively) and water-soluble C (WSC) were determined. While NT macroaggregates showed methanotrophic activity, CT macroaggregates acted as net CH4 producers. However, no significant differences were found between tillage systems on the fluxes and cumulative emissions of CO2 and N2O. Greatest cumulative CO2 emissions, macroaggregate-C concentration and WSC were found in the organic N fertilization treatment and the lowest in the control treatment. Moreover, a tillage and N fertilization interactive effect was found in macroaggregate CO2 production: while the different types of N fertilizers had no effects on the emission of CO2 in the NT macroaggregates, a greater CO2 production in the CT macroaggregates was observed for the organic fertilization treatment compared with the mineral and control treatments. The highest N2O losses' due to nitrification were found in the mineral N treatment while denitrification was the main factor affecting N2O losses in the organic N treatment. Our results suggest that agricultural management practices such as tillage and N fertilization regulate GHG production in macroaggregates through changes in the proportion of C and N substrates and in microbial activity. (C) 2013 Elsevier Ltd. All rights reserved.
  • Authors:
    • Barsotti, J. L.
    • Sainju, U. M.
    • Wang, J.
  • Source: Soil Science Society of America Journal
  • Volume: 78
  • Issue: 1
  • Year: 2014
  • Summary: Little information is available about management practice effects on the net global warming potential (GWP) and greenhouse gas intensity (GHGI) under dryland cropping systems. We evaluated the effects of cropping sequences (conventional-tillage malt barley [Hordeum vulgaris L.]-fallow [CTB-F], no-till malt barley-pea [Pisum sativum L.] [NTB-P], and no-till continuous malt barley [NTCB]) and N fertilization rates (0 and 80 kg N ha(-1)) on net GWP and GHGI from 2008 to 2011 in eastern Montana. Carbon dioxide sources from farm operations were greater under CTB-F than NTB-P and NTCB and greater with N fertilization than without, but the sources from soil greenhouse gases (GHGs) varied among treatments and years. Carbon dioxide sinks from crop residue and soil organic C (SOC) sequestration were greater under NTB-P or NTCB with 80 kg N ha(-1) than other treatments. Net GWP and GHGI based on soil respiration (GWP(R) and GHGI(R), respectively) and SOC (GWP(C) and GHGI(C), respectively) were greater under CTB-F with 0 kg N ha(-1) than other treatments, suggesting that alternate-year fallow and the absence of N fertilization to crops can increase net GHG emissions. Because of greater grain yield but lower GWP and GHGI, NTB-P with N rates between 0 and 80 kg N ha(-1) may be used as management options to mitigate global warming potential while sustaining dryland malt barley and pea yields compared with CTB-F with 0 kg N ha(-1) in the northern Great Plains. The results can be applied to other semiarid regions with similar soil and climatic conditions.
  • Authors:
    • McDonald, A. J.
    • Bishnoi, D. K.
    • Kumar, A.
    • Jat, M. L.
    • Majumdar, K.
    • Sapkota, T. B.
    • Pampolino, M.
  • Source: Field Crops Research
  • Volume: 155
  • Year: 2014
  • Summary: In the high-yielding wheat production systems in Northwest (NW) Indo-Gangetic Plains of India, intensive tillage operations and blanket fertilizer recommendations have led to high production costs, decreased nutrient use efficiency, lower profits and significant environmental externalities. No-tillage (NT) has been increasingly adopted in this region to reduce costs and increase input use efficiency. But, optimal nutrient management practices for NT based wheat production are still poorly understood. Opportunities exist to further enhance the yield, profitability, and resource use efficiency of NT wheat through site-specific nutrient management (SSNM). On-farm trials were conducted in seven districts of Haryana, India for two consecutive years (2010-11 and 2011-12) to evaluate three different approaches to SSNM based on recommendations from the Nutrient Expert (R) (NE) decision support system in NT and conventional tillage (CT) based wheat production systems. Performance of NE based recommendations was evaluated against current state recommendations and farmers' practices for nutrient management. Three SSNM treatments based on NE based recommendation were (1) 'NE80:20' with 80% N applied at planting and 20% at second irrigation (2) 'NE33:33:33' with N split as 33% basal, 33% at Crown Root Initiation (CRI) and 33% at second irrigation; and (3) 'NE80:GS' with N split as 80% basal and further application of N based on optical sensor (Green Seeker (TM))-guided recommendations. Yield, nutrient use efficiency and economic profitability were determined following standard agronomic and economic measurements and calculations. Cool Farm Tool (CET), an empirical model to estimate greenhouse gases (GHGs) from agriculture production, was used to estimate GHG emissions under different treatments. Wheat grain and biomass yield were higher under NT in 2010-11 but no difference was observed in 2011-12. The three NE-based nutrient management strategies increased yield, nutrient use efficiency as well as net return as compared to state recommendation and farmers' fertilization practice. Global warming potential (GWP) of wheat production was also lower with NT system as compared to CT system and NE-based nutrient managements as compared to farmers' fertilization practice. State recommended nutrient management had similar GWP as NE-based nutrient managements except NE80:GS in which GWP was the lowest. Results suggest that no-tillage system along with site-specific approaches for nutrient management can increase yield, nutrient use efficiency and profitability while decreasing GHG from wheat production in NW India.
  • Authors:
    • Jin, V. L.
    • Mitchell, R. B.
    • Follett, R. F.
    • Varvel, G. E.
    • Vogel, K. P.
    • Schmer, M. R.
  • Source: PLOS ONE
  • Volume: 9
  • Issue: 3
  • Year: 2014
  • Summary: Low-carbon biofuel sources are being developed and evaluated in the United States and Europe to partially offset petroleum transport fuels. Current and potential biofuel production systems were evaluated from a long-term continuous no-tillage corn (Zea mays L.) and switchgrass (Panicum virgatum L.) field trial under differing harvest strategies and nitrogen (N) fertilizer intensities to determine overall environmental sustainability. Corn and switchgrass grown for bioenergy resulted in near-term net greenhouse gas (GHG) reductions of -29 to -396 grams of CO2 equivalent emissions per megajoule of ethanol per year as a result of direct soil carbon sequestration and from the adoption of integrated biofuel conversion pathways. Management practices in switchgrass and corn resulted in large variation in petroleum offset potential. Switchgrass, using best management practices produced 3919 +/- 117 liters of ethanol per hectare and had 74 +/- 2.2 gigajoules of petroleum offsets per hectare which was similar to intensified corn systems (grain and 50% residue harvest under optimal N rates). Co-locating and integrating cellulosic biorefineries with existing dry mill corn grain ethanol facilities improved net energy yields (GJ ha(-1)) of corn grain ethanol by >70%. A multi-feedstock, landscape approach coupled with an integrated biorefinery would be a viable option to meet growing renewable transportation fuel demands while improving the energy efficiency of first generation biofuels.
  • Authors:
    • Dalgaard, R.
    • Petersen, B. M.
    • Oudshoorn, F. W.
    • Halberg, N.
    • Sorensen, C. G.
  • Source: Biosystems Engineering
  • Volume: 120
  • Issue: April
  • Year: 2014
  • Summary: Different tillage systems result in different resource uses and environmental impacts. Reduced tillage generates savings in direct energy input and the amount of machinery items needed. As the basics for holistic Life Cycle Assessments, both the influencing direct and indirect energy as sources of greenhouse gas emissions are required. Life Cycle inventories (LCI) were aggregated for a number of optimised machinery systems and tillage scenarios integrating a four crop rotation consisting of spring barley, winter barley, winter wheat and winter rape seed. By applying Life Cycle Assessments to a number of tillage scenarios and whole field operations sequences, the energy efficiency and environmental impact in terms of greenhouse gas emissions (GHG) were evaluated. Results showed that the total energy input was reduced by 26% for the reduced tillage system and by 41% for the no-tillage system. Energy used for traction and machine construction contributed between 6 and 8% of the total GHG emission per kg product. The total emission of GHG was 915 g CO2 equivalents per kg product by using the conventional tillage system, 817 g CO2 equivalents for the reduced tillage system and 855 g CO2 equivalents for the no tillage system. The no tillage system was expected to yield 10% less. The mineralisation in the soil contributed the most (50-60%) to this emission, while the fertiliser production contributed with 28-33%. The results stress the importance of applying a systems approach to capture the implications of, for example, sustained yields as otherwise the environmental benefits can be compromised. (C) 2014 IAgrE. Published by Elsevier Ltd. All rights reserved.
  • Authors:
    • Nevison, I. M.
    • McKenzie, B. M.
    • Hallett, P. D.
    • Gordon, H.
    • Watson, C. A.
    • Rees, R. M.
    • Walker, R. L.
    • Wheatley, R.
    • Topp, C. F. E.
    • Griffiths, B. S.
    • Ball, B. C.
  • Source: Agriculture, Ecosystems & Environment
  • Volume: 189
  • Issue: May
  • Year: 2014
  • Summary: Soil management practices shown to increase carbon sequestration include reduced tillage, amendments of carbon and mixed rotations. As a means to mitigate greenhouse gases, however, the success of these practices will be strongly influenced by nitrous oxide (N2O) emissions that vary with soil wetness. Few seasonal data are available on N2O under different soil managements so we measured seasonal N2O emission in three field experiments between 2006 and 2009 in eastern Scotland. The experimental treatments at the three sites were (1) tillage: no-tillage, minimum tillage, ploughing to 20 cm with or without compaction and deep ploughing to 40 cm, (2) organic residue amendment: application of municipal green-waste compost or cattle slurry and (3) rotations: stocked and stockless (without manure) organic arable farming rotations. Most seasons were wetter than average with 2009 the wettest, receiving 20-40% more rainfall than average. Nitrous oxide emissions were measured using static closed chambers. There was no statistical evidence, albeit with low statistical power, that reduced tillage affected N2O emissions compared to normal depth ploughing. With organic residue amendments, only in the wet season in 2008 were emissions significantly increased by high rates of green-waste compost (4.5 kg N2O-N ha(-1)) and cattle slurry (5.2 kg N2O-N ha(-1)) compared to the control (1.9 kg N2O-N ha(-1)). In the organic rotations, N2O emissions were greatest after incorporation of the grass/clover treatments, especially during conversion of a stocked rotation to stockless. Emissions from the organic arable crops (1.9 kg N2O-N ha(-1) in 2006, 3.0 kg N2O-N ha(-1) in 2007) generally exceeded those from the organic grass/clover (0.8 kg N2O-N ha(-1) in 2006, 1.1 kg N2O-N ha(-1) in 2007) except in 2008 when the Wet weather delayed manure applications and increased emissions from the grass/clover (2.8 kg N2O-N ha(-1)). Nevertheless, organic grassland was the land use providing the most effective overall mitigation. Although the magnitude of fluxes did not relate particularly well to rainfall differences between seasons, greater rainfall received during some growing seasons increased the differences between tillage, organic residue and crop rotation phase treatments, negating any possible mitigation by timing management operations in dry periods. This was partly attributed to applying tillage and manures late and/or in wet conditions. Of benefit would be different sampling strategies including closed chambers or eddy covariance with standardised methodology. Controlled soil management experiments with a wide geographic spread to specify land management for mitigation also important. (C) 2014 Elsevier B.V. All rights reserved.