• Authors:
    • Tibbett, M.
    • Hobbs, R. J.
    • Harper, R. J.
    • George, S. J.
  • Source: Agriculture Ecosystems and Environment
  • Volume: 163
  • Year: 2012
  • Summary: Transformation of the south-western Australian landscape from deep-rooted woody vegetation systems to shallow-rooted annual cropping systems has resulted in the severe loss of biodiversity and this loss has been exacerbated by rising ground waters that have mobilised stored salts causing extensive dry land salinity. Since the original plant communities were mostly perennial and deep rooted, the model for sustainable agriculture and landscape water management invariably includes deep rooted trees. Commercial forestry is however only economical in higher rainfall (>700 mm yr -1) areas whereas much of the area where biodiversity is threatened has lower rainfall (300-700 mm yr -1). Agroforestry may provide the opportunity to develop new agricultural landscapes that interlace ecosystem services such as carbon mitigation via carbon sequestration and biofuels, biodiversity restoration, watershed management while maintaining food production. Active markets are developing for some of these ecosystem services, however a lack of predictive metrics and the regulatory environment are impeding the adoption of several ecosystem services. Nonetheless, a clear opportunity exists for four major issues - the maintenance of food and fibre production, salinisation, biodiversity decline and climate change mitigation - to be managed at a meaningful scale and a new, sustainable agricultural landscape to be developed.
  • Authors:
    • Mitchell, C. D.
    • Sochacki, S. J.
    • George, S. J.
    • Dean, C.
    • Tibbett, M.
    • Stilwell, A. T.
    • Okom, A. E. A.
    • Harper, R. J.
    • Mann, S. S.
    • Dods, K.
  • Source: Agriculture, Ecosystems & Environment
  • Volume: 163
  • Year: 2012
  • Summary: In the Western Australian wheatbelt, the restoration of native eucalypt forests for managing degraded agricultural landscapes is a critical part of managing dryland salinity and rebuilding biodiversity. Such reforestation will also sequester carbon. Whereas most investigative emphasis has been on carbon stored in biomass, the effects of reforestation on soil organic carbon (SOC) stores and fertility are not known. Two 26 year old reforestation experiments with four Eucalyptus species ( E. cladocalyx var nana, E. occidentalis, E. sargentii and E. wandoo) were compared with agricultural sites (Field). SOC stores (to 0.3 m depth) ranged between 33 and 55 Mg ha -1, with no statistically significant differences between tree species and adjacent farmland. Farming comprised crop and pasture rotations. In contrast, the reforested plots contained additional carbon in the tree biomass (23-60 Mg ha -1) and litter (19-34 Mg ha -1), with the greatest litter accumulation associated with E. sargentii. Litter represented between 29 and 56% of the biomass carbon and the protection or utilization of this litter in fire-prone, semi-arid farmland will be an important component of carbon management. Exch-Na and Exch-Mg accumulated under E. sargentii and E. occidentalis at one site. The results raise questions about the conclusions of SOC sequestration studies following reforestation based on limited sampling and reiterate the importance of considering litter in reforestation carbon accounts.
  • Authors:
    • Lakshmanan, P.
    • Robinson, N.
    • Brackin, R.
    • Holst, J.
    • Schmidt, S.
  • Source: Agriculture Ecosystems and Environment
  • Volume: 155
  • Year: 2012
  • Summary: Addressing the limited knowledge of nitrogen (N) pools in tropical agricultural soils and the need to reduce N losses from these systems, we analysed soluble organic and inorganic N in two Hydrosols under sugarcane. Concentrations of ammonium and nitrate spanned ~3 - orders of magnitude (0.2-41.0 mg ammonium-N, 0-10.7 mg nitrate-N kg -1 soil) with the highest concentrations detected within 2-3 months of fertiliser application. Soluble amino acids spanned 1-order of magnitude (0.22-2.42 mg amino acid-N kg -1 soil) and accounted for up to 70% of the low-molecular weight N. Amino acid concentrations were usually highest in the wet season and uniform across soil depth, indicating that amino acids are generated throughout the studied profile. We compared soluble and dissolved (free) N in the soil solution in a subset of samples. In soil solution, amino acid, ammonium and nitrate concentrations averaged 20, 265 and 1820 M, respectively, corresponding to ~10% (amino acids), ~20% (ammonium) and ~100% (nitrate) of the soluble N pool. We calculated an annual gross amino acid flux in the dissolved N pool in the order of 2-6 tons N ha -1 yr -1 in the upper 40 cm of soil. We discuss whether amino acids can significantly contribute to the N demand of sugarcane.
  • Authors:
    • Armstrong, R.
    • Norton, R.
    • Chen, D. L.
    • Lam, S. K.
    • Mosier, A. R.
  • Source: Global Change Biology
  • Volume: 18
  • Issue: 9
  • Year: 2012
  • Summary: Understanding nitrogen (N) removal and replenishment is crucial to crop sustainability under rising atmospheric carbon dioxide concentration ([CO 2]). While a significant portion of N is removed in grains, the soil N taken from agroecosystems can be replenished by fertilizer application and N 2 fixation by legumes. The effects of elevated [CO 2] on N dynamics in grain crop and legume pasture systems were evaluated using meta-analytic techniques (366 observations from 127 studies). The information analysed for non-legume crops included grain N removal, residue C:N ratio, fertilizer N recovery and nitrous oxide (N 2O) emission. In addition to these parameters, nodule number and mass, nitrogenase activity, the percentage and amount of N fixed from the atmosphere were also assessed in legumes. Elevated [CO 2] increased grain N removal of C 3 non-legumes (11%), legumes (36%) and C 4 crops (14%). The C:N ratio of residues from C 3 non-legumes and legumes increased under elevated [CO 2] by 16% and 8%, respectively, but the increase for C 4 crops (9%) was not statistically significant. Under elevated [CO 2], there was a 38% increase in the amount of N fixed from the atmosphere by legumes, which was accompanied by greater whole plant nodule number (33%), nodule mass (39%), nitrogenase activity (37%) and %N derived from the atmosphere (10%; non-significant). Elevated [CO 2] increased the plant uptake of fertilizer N by 17%, and N 2O emission by 27%. These results suggest that N demand and removal in grain cropping systems will increase under future CO 2-enriched environments, and that current N management practices (fertilizer application and legume incorporation) will need to be revised.
  • Authors:
    • Armstrong, R.
    • Norton, R.
    • Chen, D. l.
    • Lam, S. K.
  • Source: Nutrient Cycling in Agroecosytems
  • Volume: 92
  • Issue: 2
  • Year: 2012
  • Summary: There are few reports on the effects of atmospheric carbon dioxide concentration ([CO2]) on fertilizer N recovery by crops under open-air conditions. This study was conducted at the Australian Grains Free-Air CO2 Enrichment (AGFACE) facility in southern Australia to investigate the effects of elevated [CO2] (550 mu mol mol(-1)) on growth, N uptake and fertilizer N-15 recovery by spring wheat (Triticum aestivum L. cv. Yitpi) over a 2-year period. N-15-enriched (10.22 atom%) granular urea was applied to microplots at 50 kg N ha(-1) at varying seasonal rainfall and temperature scenarios (simulated by supplementary irrigation and late sowing) for three experimental periods [2008 normal sowing (2008NS), 2008 late sowing (2008LS) and 2009 normal sowing (2009NS)]. Elevated [CO2] increased wheat biomass (27-58%), N uptake (18-44%) and amount of plant N derived from soil (20-50%) at 2008NS and 2009NS (rainfed), but the effect was not apparent at 2008LS (hotter and drier) and supplementary irrigated plots for 2009NS (above-average rainfall). Tissue N concentration and N derived from fertilizer were unaffected by elevated [CO2] in any experimental period. Irrespective of [CO2], grain yield and whole plant fertilizer N uptake was 37-94 and 13-609%, respectively, higher under supplementary irrigated plots than that in rainfed counterparts. These results indicate that more fertilizer N will need to be applied to this wheat production zone under future [CO2] environments, and yield gains in hotter and drier climates will be lower than those in higher rainfall zones.
  • Authors:
    • Kirkegaard, J. A.
    • Ryan, M. H.
  • Source: AGRICULTURE ECOSYSTEMS & ENVIRONMENT
  • Volume: 163
  • Year: 2012
  • Summary: All available data on arbuscular mycorrhizal fungi (AMF) in Australian extensive cropping systems are reviewed in an agronomic framework. In the southern temperate and northern subtropical zones, 80-85% and 60%, respectively, of cropped area is winter cereals. In the south, non-mycorrhizal winter break crops are common and crops are often rotated with low input pastures. In the north, continuous cropping with winter crops, summer crops and long (12-18 month) plant-free fallow is common. Only here does reduced colonization by AMF cause intermittent yield reductions, perhaps reflecting low phosphorus (P) soils, high crop growth rates and dry surface soil limiting P availability. Soil temperatures below 10°C may limit the contribution of AMF to southern crops. In both zones, wheat yields are generally enhanced following fallows and non-mycorrhizal break crops, even under P limitation. AMF are unlikely to aid control of root diseases or dryland salinity adaptation; their role in soil structure and carbon sequestration requires clarification. Organic crops are highly colonized, but invariably P deficient. Thus, little evidence supports consideration of AMF in farm management and many agronomic practices that underpin sustainable productivity reduce colonization. We hope this paper stimulates dialog between mycorrhizal researchers and agronomists to target high priority research.
  • Authors:
    • Pangga, I. B.
    • Chakraborty, S.
    • Roper, M. M.
  • Source: Global Change Biology
  • Volume: 18
  • Issue: 7
  • Year: 2012
  • Summary: Soil multitrophic interactions transfer energy from plants as the predominant primary producer to communities of organisms that occupy different positions in the food chain and are linked by multiple ecological networks, which is the soil food web. Soil food web sequesters carbon, cycles nutrients, maintains soil health to suppress pathogens, helps plants tolerate abiotic and biotic stress, and maintains ecosystem resilience and sustainability. Understanding the influence of climate change on soil multitrophic interactions is necessary to maintain these essential ecosystem services. But summarising this influence is a daunting task due to a paucity of knowledge and a lack of clarity on the ecological networks that constitute these interactions. The scant literature is fragmented along disciplinary lines, often reporting inconsistent findings that are context and scale-dependent. We argue for the differentiation of soil multitrophic interactions along functional and spatial domains to capture cross-disciplinary knowledge and mechanistically link all ecological networks to reproduce full functionalities of the soil food web. Distinct from litter mediated interactions in detritosphere or elsewhere in the soil, the proposed 'pathogen suppression' and 'stress tolerance' interactions operate in the rhizosphere. A review of the literature suggests that climate change will influence the relative importance, frequency and composition of functional groups, their trophic interactions and processes controlling these interactions. Specific climate change factors generally have a beneficial influence on pathogen suppression and stress tolerance, but findings on the overall soil food web are inconsistent due to a high level of uncertainty. In addition to an overall improvement in the understanding of soil multitrophic interactions using empirical and modelling approaches, we recommend linking biodiversity to function, understanding influence of combinations of climatic factors on multitrophic interactions and the evolutionary ecology of multitrophic interactions in a changing climate as areas that deserve most attention.
  • Authors:
    • Freney, J. R.
    • Chen, D.
    • Edis, R. E.
    • Turner, D. A.
    • Denmead, O. T.
  • Source: Nutrient Cycling in Agroecosystems
  • Volume: 93
  • Issue: 2
  • Year: 2012
  • Summary: As farmers in southern Australia typically apply nitrogen (N) to cereal crops by top-dressing with ammonia (NH3) based fertilizer in late winter or early spring there is the potential for large losses of NH3. This paper describes the results of micrometeorological measurements to determine NH3 loss and emission factors following applications of urea, urea ammonium nitrate (UAN), and ammonium sulfate (AS) at different rates to cereal crops at two locations in southern Australia. The amounts of NH3 lost are required for farm economics and management, whilst emission factors are needed for inventory purposes. Ammonia loss varied with fertilizer type (urea > UAN > AS) and location, and ranged from 1.8 to 23 % of N applied. This compares with the emission factor of 10 % of applied N advocated by IPCC ( 2007). The variation with location seemed to be due to a combination of factors including soil texture, soil moisture content when fertilizer was applied and rainfall after fertilizer application. Two experiments at one location, 1 week apart, demonstrated how small, temporal differences in weather conditions and initial soil water content affected the magnitude of NH3 loss. The results of these experiments underline the difficulties farmers face in timing fertilization as the potential for loss, depending on rainfall, can be large.
  • Authors:
    • Grant, T.
    • Carre, A.
    • Eady, S.
  • Source: Journal of Cleaner Production
  • Volume: 28
  • Issue: June
  • Year: 2012
  • Summary: Most agricultural products are produced on farms where there is a mix of activities, resulting in a range of co-products. This raises the issue of how best to model these complex production systems for Life Cycle Assessment, especially where there are benefits imparted by one activity in the mixed farming system to another. On the mixed farm studied, there were significant two-way reference flows (representing 288 t CO2-e/year or 10% of the total farm emissions) between activities producing distinct products (wool, meat, grain) and these were modelled using system expansion. Cropping and sheep activities were modelled as separate sub-processes in the farming system, with unique inputs and outputs identified for each. Co-production from the sheep activity was modelling using allocation, comparing biophysical and economic relationships. Using an economic allocation resulted in different estimates of global warming impact for sheep co-products, with figures varying by 7-52%. When compared to biophysical allocation, economic allocation shifted the environmental burden to the higher value co-products and away from the high resource use products. Using economic allocation, for every kilogram of wool produced there was an estimated 28.7 kg of CO2-e emitted. Amongst the live animal products, the stud rams had the highest estimated carbon footprint (719 kg CO2-e/ram). Amongst the crops, estimates of emissions for the cereal grains averaged 202 kg CO2-e/tonne grain, canola 222 kg CO2-e/tonne and lupins 510 kg CO2-e/tonne, when modelled to include the benefits of the mixed farming system. Crown Copyright (C) 2011 Published by Elsevier Ltd. All rights reserved.
  • Authors:
    • James, A.
    • Solah, V.
    • Biswas, W.
    • Gunady, M.
  • Source: Journal of Cleaner Production
  • Volume: 28
  • Year: 2012
  • Summary: A life cycle greenhouse gas (GHG) assessment of 1 kJ of strawberries, button mushrooms (Agaricus bisporus), and romaine/cos lettuces (Lactuca sativa) transported to retail outlets in Western Australia (WA) was examined and compared. The study included pre-farm, on-farm, and post-farm emissions. The pre-farm stage included GHG emissions from agricultural machinery and chemical production, and transport of raw materials (spawn, peat, and compost) in mushrooms. The on-farm stage included GHG emissions from agricultural machinery operation, chemical use, water for irrigation, waste generated, as well as electricity and energy consumption. The post-farm stage included transport of produce to Distribution Center (DC), storage in DC, and transport to retail outlets. The 'hotspots' or the stages that emit the highest GHG were determined for strawberries, button mushrooms and romaine/cos lettuces. The results have shown that the life cycle GHG emissions of strawberries and lettuces were higher than mushrooms due to intensive agricultural machinery operations during the on-farm stage. Mushrooms, however have significantly higher GHG emissions during pre-farm stage due to transport of peat, spawn, and compost. (C) 2011 Elsevier Ltd. All rights reserved.