Australian Agricultural Systems Research Articles

Exploring patterns of female house mouse spatial organisation among outbreaking and stable populations.

The size and distribution of home ranges reflect how individuals within a population use, defend, and share space and resources, and may thus be an important predictor of population-level dynamics. Eruptive species, such as the house mouse in Australian grain-growing regions, are an ideal species in which to investigate variations in space use and home range overlap between stable and outbreaking populations. In this study, we use spatially explicit capture-recapture models to explore if space use and home range overlap among female mice could serve as indicators of changes in population density leading into summer. Additionally, we assess the sensitivity of space use and home range estimates to reduced recapture rates. Our analysis did not reveal variations in the spring spatial organisation of female mice based on existing capture-mark-recapture data. However, our study highlights the need to balance monitoring efforts within regions, emphasising the importance of exploring studies that can improve spatial recaptures by optimising trapping efforts. This is particularly important in Australian agricultural systems, where varying farm management practices may drive differences in population dynamics.

Revised emission factors for estimating direct nitrous oxide emissions from nitrogen inputs in Australia’s agricultural production systems: a meta-analysis

Context Agricultural soils are a major source of emissions of the greenhouse gas nitrous oxide (N2O). Aim Quantify direct N2O emissions from Australian agricultural production systems receiving nitrogen (N) inputs from synthetic and organic fertilisers, crop residues, urine and dung. Method A meta-analysis of N2O emissions from Australian agriculture (2003–2021) identified 394 valid emission factors (EFs), including 102 EFs with enhanced efficiency fertilisers (EEFs). Key results The average EF from all N sources (excluding EEFs) was 0.57%. Industry-based EFs for synthetic N fertiliser (excluding EEFs) ranged from 0.17% (non-irrigated pasture) to 1.77% (sugar cane), with an average Australia-wide EF of 0.70%. Emission factors were independent of topsoil organic carbon content, bulk density and pH. The revised EF for the non-irrigated cropping (grains) industry is now 0.41%; however, geographically-defined EFs are recommended. Urea was the most common N source with an average EF of 0.72% compared to urine (0.20%), dung (0.06%) and organo-mineral mixtures (0.26%). The EF for synthetic N fertilisers in rainfed environments increased by 0.16% for every 100 mm over 300 mm mean annual rainfall. For each additional 50 kg N ha−1 of synthetic fertiliser, EFs increased by 0.13%, 0.31% and 0.38% for the horticulture, irrigated and high rainfall non-irrigated cropping industries, respectively. The use of 3,4 dimethylpyrazole-phosphate (DMPP) produced significant reductions in EFs of 55%, 80% and 84% for the horticulture, non-irrigated and irrigated cropping industries, respectively. Conclusions and implications Incorporation of the revised EFs into the 2020 National Greenhouse Accounts (NGA) produced a 12% increase in direct N2O emissions from the application of synthetic N fertilisers. The lack of country-specific crop residue decomposition data is a major deficiency in the NGA.

Breaking hard seed dormancy in the perennial legume Lebeckia ambigua E. Mey. to enhance sustainable agricultural production

In this study, seeds of Lebeckia ambigua E. Mey., a South African perennial legume, displayed a high level of physical dormancy, commonly termed ‘hardseededness’. In Australian agricultural systems, this trait is exploited in annual legumes to ensure their regeneration after a cropping phase. While hardseededness in annual legumes has been studied extensively, there have been fewer studies of this feature in perennial legumes. Here, for the first time, we examine the conditions required for hard seed breakdown in L. ambigua, with experiments undertaken in both the field and laboratory. The annual legumes Ornithopus sativus Brot. and Biserrula pelecinus L. were included for comparison. More than 50% of the hard seed of L. ambigua, when buried at 0.5 cm for 87 weeks, remained hard, and 25% were still hard after 188 weeks. We are also the first to demonstrate genetic variation in hard seed breakdown patterns of L. ambigua when buried at 0.5 cm. In the laboratory, L. ambigua seed softened after exposure to a temperature of 80°C for 2–8 days in a dry oven and also after reaching 60°C in a cycling temperature oven, with fluctuating humidity. Seed of L. ambigua produced in two different geographic regions of Western Australia and then buried at 0.5 or 4 cm in the soil, at two softening locations, became differentially soft over 188 weeks. There was a significant three-way interaction between burial depth, site and maternal influences (P<0.01) on hard seed breakdown. The pattern of hard seed breakdown revealed in this perennial legume reflects that described for pyrogenic species and does not fit the models developed by agricultural researchers for annual legumes. Understanding the ecological triggers for release of seeds of L. ambigua from dormancy has provided opportunities for exploitation of this trait in future sustainable agricultural development.

Phytophthora root rot of chickpea: inoculum concentration and seasonally dependent success for qPCR based predictions of disease and yield loss

Phytophthora root rot (PRR) caused by Phytophthora medicaginis (Pm) is an important disease of chickpea in Australia. There are limited control options, with avoiding planting chickpeas in paddocks with a high PRR risk a key management strategy. Currently, risk assessment is based solely on paddock history of PRR, without any measure of Pm inoculum. We developed a qPCR test to quantify Pm inoculum concentrations in soil and evaluated its ability to predict, prior to planting, PRR disease and yield loss in chickpea. The qPCR test was specific to Pm and did not cross react with other Phytophthora species found in Australian agricultural systems and was sensitive, being able to detect <1 Pm oospore/g soil. A field experiment showed no correlation between Pm DNA concentration at seeding and PRR development on the susceptible chickpea variety, Sonali. Field experiments with Yorker, a PRR moderately resistant variety, showed Pm DNA concentration at seeding was correlated with PRR development and grain yield, but relationships varied with season and soil moisture (2015, irrigated r2 0.752, dryland r2 0.532; 2017 irrigated r2 0.52, dryland r2 0.0005), however above average rainfall in 2016 was highly conducive to PRR and there was no relationship between Pm DNA concentrations at seeding and PRR development or yield. The qPCR could detect moderate to high levels of Pm inoculum, but not low levels capable of causing disease and yield loss in conducive seasons. The Pm qPCR test showed potential to support in-field diagnostics.

Do mass flowering agricultural species affect the pollination of Australian native plants through localised depletion of pollinators or pollinator spillover effects?

Australian agricultural landscapes are dominated by northern-hemisphere mass flowering species, with the potential to disrupt pollination of adjacent co-flowering plants. In northern-hemisphere systems, mass flowering plants can act as ‘pollinator magnets’. Magnets can reduce the pollination success of adjacent co-flowering neighbours by drawing pollinators from these plants. However, magnets can also produce pollination ‘spillover-effects’ through increased pollinator movements to adjacent co-flowering taxa, potentially either increasing pollination or impacting it through transfer of mixed-species pollen. The impact of agricultural species on co-flowering plants in Australia is unknown. Native Australian plants evolved with unique pollinators and yet agricultural pollination is dominated by the exotic honeybee Apis mellifera. We tested how distance (to 250 m) from each of two populations of Lavender (Lavandula spp.) (2 years), Nectarines (Prunus persica var. nucipersica or var. nectarina) (1 year) and the pasture weed Paterson’s Curse (Echium plantagineum) (2 years) affected pollinator diversity and abundance within experimental arrays of native and northern-hemisphere plants. For Paterson’s Curse, we tested whether visitation varied when honeybee abundance was experimentally increased. As expected, we found magnets attracted significantly more honeybee visits in all possible comparisons across combinations of species, sites and years. However, contrary to expectation, in 10 of 18 comparisons, co-flowering species supported a slightly higher diversity of pollinators than magnets, with honeybees comprising a significantly lower proportion of flower visitors in 14 comparisons. The exceptions, which included populations of all three magnet species, were cases where honeybees were the only visitor (6 comparisons) or the magnet and co-flowering species were each visited by a single but different pollinator (2 compariosns). Most strikingly, our data provided no evidence of pollinator spillover. More than 95% of all pollinators on co-flowering species carried only their pollen and overall pollinator abundance didn’t vary significantly with distance from magnets at any site or time. Honeybee abundance did not vary significantly with distance from magnets. For Paterson’s Curse, the addition of managed hives increased honeybee abundance on co-flowering species in two of eight cases, but pollinator abundance didn’t vary with distance from the magnet. Overall, we found few direct effects of mass flowering agricultural species on the pollination of either Australian native or exotic neighbours. The lack of spillover-effects may largely reflect the unusually high species fidelity of foraging A. mellifera. However, the numerical dominance of honeybees within Australian agricultural systems may impact pollination at the regional level.

Evaluating monitoring, evaluation and learning initiatives in the New Zealand and Australian agricultural research and innovation systems: The MEL2 framework

The potential for monitoring, evaluation and learning (MEL) to enhance innovation and impact in agricultural research and development is receiving increasing attention. New Zealand’s AgResearch Limited and Australia’s CSIRO Agriculture and Food are working with their scientists to support the organisations to achieve greater innovation and impact by embedding MEL into research programs and projects. However, both organisations have found it challenging to systematically demonstrate the value of their MEL initiatives. While there is an increasing number of case studies and anecdotes pointing towards the contribution of MEL to fostering innovation that delivers social, economic and environmental impacts, there is limited evidence, collated through systematic and rigorous methods, to substantiate this. This article presents an evaluation framework drawing on insights from complexity science (the Cynefin framework), evaluation practice and research (complexity-aware M&amp;E and reflective practice) and innovation capacities (learning, reflection and adaptation). The framework is intended for research organisations working in agricultural innovation systems to be able to demonstrate the value of their MEL initiatives as well as carry out comparative analyses. It also supports organisational learning to better inform evaluative strategies and actions.

Projected changes in drought across the wheat belt of southeastern Australia using a downscaled climate ensemble

Drought is viewed as a naturally recurring phenomenon in many Australian agricultural systems. Identifying regional changes in frequency and severity of drought induced by climate change is required to develop regionally specific adaptation strategies. In this study, we provided a first look at the impacts of climate change on 21st century drought characteristics over the New South Wales wheat belt of southeastern Australia. These impacts were assessed from an ensemble of 28 statistical downscaled global climate models under representative concentration pathway (RCP8.5). A modified relative standardized precipitation and evapotranspiration index (rSPEI) at the seasonal scale (3 months) was used to analyse temporal and spatial changes in drought. Results indicated that there was a tendency towards more frequent and severe winter–spring droughts over the study area. Moreover, winter–spring drought prone areas were expected to expand from west to east. Until the end of the 21st century, more than half the wheat belt would be vulnerable to winter–spring drought. The combined effects of reduced precipitation and increased temperature during future winter and spring seasons were the main reasons causing these changes of drought. In addition, summer and autumn droughts would have both slight temporal and spatial changes across the study region. This study also revealed that traditionally dry areas would likely experience an increased frequency of drought compared to wetter areas when subjected to a same increase in temperature or decrease in precipitation. Furthermore, the western part of the wheat belt might be unsuitable for winter crops in the future, or at least exposed to an increased risk of variable yield and would require a gradual transformation which might include summer crops or pastures. Investments in cropping land should be focused on the east part of the wheat belt to achieve more consistent financial returns.

Complete chloroplast genome of glyphosate resistant Sonchus oleraceus L. from Australia, with notes on the small single copy (SSC) region orientation

Sonchus oleraceus, common sowthistle, is an asteraceous weed in Australian agricultural systems and has recently developed resistance to glyphosate. We present the complete chloroplast sequence of S. oleracueus reconstructed from Illumina whole genome shotgun sequencing. This is the first complete chloroplast genome available for the genus Sonchus. The complete chloroplast sequence is 151,808 bp long. A Bayesian phylogeny of the chloroplast coding regions of the tribe Cichorieae (Asteraceae) is presented. The S. oleraceus chloroplast genome is deposited at GenBank under accession number MG878405.

Impacts of windbreak shelter on crop and livestock production

Agroforestry (the integration of trees into agricultural landscapes) has been promoted, in Australia and elsewhere, as a way to increase farm productivity by providing a wide range of benefits. Despite this, adoption of agroforestry in Australian agricultural systems remains low. To implement agroforestry, farmers must be convinced the benefits of including trees outweigh the costs. This review evaluates the available quantitative data on shelter benefits with emphasis on Australian conditions, identifies key research gaps and determines if there is sufficient knowledge to make accurate predictions about impacts on farm productivity. Availability of quantitative data on windbreak shelter benefits was examined in five key areas; water use and evaporation, crop/pasture production, livestock mortality, livestock productivity and the capacity to model impacts of windbreaks on crop/livestock systems. Good quantitative data exists for many areas, particularly for changes in environmental conditions following tree establishment, however there were many gaps in key areas. Importantly, the ability to predict crop growth under spatially and temporally variable environmental conditions and the impact of windbreaks on livestock productivity is not yet able to be meaningfully quantified. Thus modelling the profitability of windbreaks is difficult and existing models require additional quantitative data to validate and improve them.

Complete chloroplast genome of glyphosate resistant Conyza bonariensis (L.) Cronquist from Australia

Conyza bonariensis, flaxleaf fleabane, is a serious weed in Australian agricultural systems, particularly the north-east cropping system. We present the complete chloroplast sequence of C. bonariensis reconstructed from Illumina whole genome shotgun sequencing. This is the first complete chloroplast genome available for genus Conyza. The complete chloroplast sequence is 153,014 bp long, and has the same gene content and structure as other members of the tribe Astereae. A Bayesian phylogeny of the chloroplast coding regions of 18 representatives of Astereae is presented. The C. bonariensis chloroplast genome is deposited at GenBank under accession number MF276802.

Incorporating grain legumes in cereal-based cropping systems to improve profitability in southern New South Wales, Australia

Grain legumes, such as lupins and field peas, are one of key rotation components in Australian agricultural systems, supplying nitrogen (N) to following crops, and potentially increasing farm profitability. In this study, we used a modelling approach to investigate the profitability of incorporating field pea (Pisum sativum) and narrowleaf lupin (Lupinus angustifolius) in cereal-based (wheat/canola) cropping systems in southern New South Wales (NSW), Australia. We calibrated and validated the Agricultural Production Systems sIMulator (APSIM) with three-year's experimental data to predict yields of field pea and lupin, and N contribution of grain legumes in cereal-based (wheat/canola) crop rotations. We conducted a gross margin analysis to analyse the profitability of adding grain legumes into cereal-based crop rotations at both crop and rotation levels. The simulated results showed that field pea and lupin could contribute 30–65kgNha−1 to the next crop and 60–110kgNha−1 to subsequent crops (wheat/canola) for two years, corresponding to 30–55% and 60–86% of net N inputs of legume-fixed N, respectively. This greatly increased the yields and profitability of wheat/canola in the following two years. Including grain legumes in cereal-based crop rotations was more profitable than non-legume crop rotations, even though the grain legumes were less profitable than wheat/canola in the year of growing. However, N and economic benefits would be reduced to zero if N fertilizer applied to wheat/canola was over the optimal level, i.e. 100–125kgNha−1 in terms of N benefit, or 75kgNha−1 for farm-economic profit. In general, incorporation of grain legumes into cereal-based crop rotations offers an obvious N benefit to subsequent crops and provides an economic benefit for farmers (reduced N applications). This suggests that the contribution of grain legumes to cereal-based cropping systems should be assessed as part of a rotation rather than as a stand-alone crop.

Aviation biofuel from integrated woody biomass in southern Australia

A synthesis of work on integrating short‐rotation biomass plantings into existing mixed crop and livestock farming regimes with the biomass being converted to biofuels, including aviation fuel, is provided. This agroforestry system, based on mallee eucalypt species native to Australia, provides broader environmental benefits, including biodiversity protection. These species are suited to the edaphic and climatic conditions of rainfed farming systems in southern Australia. The study focused on the Great Southern region of Western Australia, with an average annual rainfall of 400–600 mm. Compared to other locations in Australia, significantly more research and development has been conducted in this region, with a mallee biomass‐to‐jet fuel business case and farmer cooperation providing reliable data for assessing the viability and sustainability of commercial supply chain development. The limited capacity of Australian agricultural systems to produce biomass due to the relatively dry climate means that the available biomass resources should be directed to strategically important energy uses such as aviation fuel. Technical, economic, and environmental insights gained from these long‐term studies have demonstrated that it is feasible to integrate this new production system into the overall farming enterprise and indicate strong prospects for a biomass industry in this region should political and economic uncertainties currently facing the renewable energy industry in Australia be resolved. WIREs Energy Environ 2017, 6:e221. doi: 10.1002/wene.221This article is categorized under: Bioenergy &gt; Science and Materials Bioenergy &gt; Economics and Policy Bioenergy &gt; Systems and Infrastructure

Australian native shrubs: Delivering benefits to livestock, soil, plants and people

s / Journal of Nutrition & Intermediary Metabolism 1 (2014) 1e55 6 marine products, particularlyfishmeal andfish oil, to beingmainly based on terrestrial products. One of the most important on-going strategies for feeding aquaculture is continually refining feeds to ensure they remain sustainable. This is especially the case for intensive aquaculture systems that rely on formulated manufactured aquafeeds. Ingredient screening and development underpin this and sit alongside other strategies to improve animal performance and increase how efficiently feeds are used. Aquaculture has global reach and offers aquaculture systems that are appropriate in different regions depending on environmental, cultural and socio-economic factors. For Atlantic salmon, off-shore and land-based systems are being discussed. Location-specific integrated multi-trophic aquaculture provides one direction with great promise, it also reflects the 3000 year old history of aquaculture that achieved an elegant solution through integrated polyculture. Funding source(s): N/A.

An open-access method for targeting revegetation based on potential for emissions reduction, carbon sequestration and opportunity cost

We propose a simple heuristic that uses open-access models and government data on agricultural activities to estimate total carbon emissions from agriculture, the gross carbon benefit and the opportunity cost per tonne CO2-e from revegetating to environmental plantings or plantation forestry. We test this across ten areas of mixed land-use that represent diverse Australian agricultural systems along a rainfall transect. The local value of agricultural production was obtained from government statistics and used to estimate the current economic opportunity cost of converting cleared agricultural land to mixed environmental plantings for carbon sequestration. Gross carbon benefit from revegetation was closely related to current agricultural use, as was financial opportunity cost. These were not related simply to site productivity potential or rainfall. The proportion of land cleared for agriculture that would need to be re-vegetated to achieve a localised zero-carbon land-use scenario was calculated by the ratio of current agricultural emissions to gross carbon benefit from revegetation; this ranged from 13% to 66% for groups of agricultural industries across Australian rainfall transects. While the heuristic does not capture the detail of models built specifically for local research questions it does provide a different lens on the questions policy makers and land managers may ask about the costs and benefits of revegetating agricultural land, and provides open-access methods to guide them.

Modeling the cadmium balance in Australian agricultural systems in view of potential impacts on food and water quality

The historical build up and future cadmium (Cd) concentrations in top soils and in crops of four Australian agricultural systems are predicted with a mass balance model, focusing on the period 1900–2100. The systems include a rotation of dryland cereals, a rotation of sugarcane and peanuts/soybean, intensive dairy production and intensive horticulture. The input of Cd to soil is calculated from fertilizer application and atmospheric deposition and also examines options including biosolid and animal manure application in the sugarcane rotation and dryland cereal production systems. Cadmium output from the soil is calculated from leaching to deeper horizons and removal with the harvested crop or with livestock products. Parameter values for all Cd fluxes were based on a number of measurements on Australian soil–plant systems. In the period 1900–2000, soil Cd concentrations were predicted to increase on average between 0.21mgkg−1 in dryland cereals, 0.42mgkg−1 in intensive agriculture and 0.68mgkg−1 in dairy production, which are within the range of measured increases in soils in these systems. Predicted soil concentrations exceed critical soil Cd concentrations, based on food quality criteria for Cd in crops during the simulation period in clay-rich soils under dairy production and intensive horticulture. Predicted dissolved Cd concentrations in soil pore water exceed a ground water quality criterion of 2μgl−1 in light textured soils, except for the sugarcane rotation due to large water leaching fluxes. Results suggest that the present fertilizer Cd inputs in Australia are in excess of the long-term critical loads in heavy-textured soils for dryland cereals and that all other systems are at low risk. Calculated critical Cd/P ratios in P fertilizers vary from <50 to >1000mgCdkgP−1 for the different soil, crop and environmental conditions applied.

Establishment and survival of the South African legume Lessertia spp. and rhizobia in Western Australian agricultural systems

Background and aims The South African herbaceous legume species Lessertia capitata, L. diffusa, L. excisa L. incana and L. herbacea were introduced to Australia to assess plant establishment and survival, as well as the saprophytic ability of their root nodule bacteria (RNB). Methods Five Lessertia spp., were inoculated with selected RNB strains and were sown in five different agroclimatic areas of the Western Australian wheatbelt during 2007 and 2008. Plant population and summer survival were evaluated in situ. Soil samples and nodules from host plants were also taken from each site. The re-isolated rhizobia were RPO1-PCR fingerprinted and their partial dnaK and nodA genes were sequenced to confirm their identity. Results Plants achieved only poor establishment followed by weak summer survival. More than 83 % of the rhizobia re-isolated from Lessertia did not correlate with the original inoculants’ fingerprints, and were identified as Rhizobium leguminosarum. The nodA sequences of the naturalised strains were also

Soil Organic Carbon, Biochar, and Applicable Research Results for Increasing Farm Productivity under Australian Agricultural Conditions

The conversion of vegetative biomass waste to biochar (biologically derived charcoal) is a source of carbon (C) that can be used to increase the level of soil organic C (SOC) in agricultural soils. This review collates available research into the effects of biologically derived C species with respect to the direct and indirect effects on agricultural productivity and their potential for use in Western Australian agricultural systems. There is a growing requirement to quantify the effect of specific biochar applications for agroecological purposes and to verify biosequestered C for climate-change-mitigation activities. This work provides a review and assessment of safe biochar application rates and examines the present levels of scientific uncertainty surrounding the efficacy and reliability of applying biochar to soils in relation to crop productivity.

Life cycle assessment of Australian sugarcane production with a focus on sugarcane growing

Past life cycle assessments (LCA) of sugarcane (Saccharum officinarum) production have commonly been based on limited datasets, and variability has not been well described. In this work, Australian sugarcane production was assessed more comprehensively in order to generate a robust set of LCA results for use in subsequent assessments of sugarcane products and also to investigate: (1) variability due to regional differences, (2) factors influencing variability, and (3) significance of the impacts. An average scenario for Australian sugarcane production was modeled based on data for the state of Queensland (98% of Australian production). Life cycle impact assessment (LCIA) results were generated using Impact 2002+, modified to be more representative of Australian conditions, and with the inclusion of water use and land use indicators. A Monte Carlo uncertainty analysis, using minimum and maximum values for production data, was undertaken to evaluate variability. Different regional production practices were also modeled to identify factors that influence variability. Normalization aimed to show the significance of total Australian sugarcane production relative to total Australian impacts. Considerable variability was found in the LCIA results, with the key variables being yield, N use efficiency, the susceptibility of soils to N leakage, irrigation (water and energy intensity), and pre-harvest burning. N leakage was found to be an important issue that influences a range of impact categories. When normalized against total national impacts, water use and land use appear to be the most significant impacts (based on simple indicators of consumption), followed by eutrophication potential, acidification potential, and respiratory impacts, whereas non-renewable energy input and global warming are less significant. The results suggest that toxicity impacts are insignificant; however, this may not be supported by other observations that link pesticide loss from sugarcane to toxicity concerns in receiving waters and is a subject for further research. The potential for significant variability in the impacts from sugarcane growing suggests a need for LCAs of sugarcane systems to consider ranges for key variables. The key variables and significant impacts identified in this work can guide data collection priorities for future assessment of sugarcane and possibly other Australian cropping systems. To further develop LCA as a useful predictive tool for Australian agricultural systems, further development and testing of impact assessment models for eutrophication, toxicity, and land and water resource depletion appropriate for Australia and its subregions will be required.

The potential contribution of forage shrubs to economic returns and environmental management in Australian dryland agricultural systems

In face of climate change and other environmental challenges, one strategy for incremental improvement within existing farming systems is the inclusion of perennial forage shrubs. In Australian agricultural systems, this has the potential to deliver multiple benefits: increased whole-farm profitability and improved natural resource management. The profitability of shrubs was investigated using Model of an Integrated Dryland Agricultural System (MIDAS), a bio-economic model of a mixed crop/livestock farming system. The modelling indicated that including forage shrubs had the potential to increase farm profitability by an average of 24% for an optimal 10% of farm area used for shrubs under standard assumptions. The impact of shrubs on whole-farm profit accrues primarily through the provision of a predictable supply of ‘out-of-season’ feed, thereby reducing supplementary feed costs, and through deferment of use of other feed sources on the farm, allowing a higher stocking rate and improved animal production. The benefits for natural resource management and the environment include improved water use through summer-active, deep-rooted plants, and carbon storage. Forage shrubs also allow for the productive use of marginal soils. Finally, we discuss other, less obvious, benefits of shrubs such as potential benefits on livestock health. The principles revealed by the MIDAS modelling have wide application beyond the region, although these need to be adapted on farm and widely disseminated before potential contribution to Australian agriculture can be realized.

Limitations of soil microbial biomass carbon as an indicator of soil pollution in the field

The size of the soil microbial biomass carbon (SMBC) has been proposed as a sensitive indicator for measuring the adverse effects of contaminants on the soil microbial community. In this study of Australian agricultural systems, we demonstrated that field variability of SMBC measured using the fumigation–extraction procedure limited its use as a robust ecotoxicological endpoint. The SMBC varied up to 4-fold across control samples collected from a single field site, due to small-scale spatial heterogeneity in the soil physicochemical environment. Power analysis revealed that large numbers of replicates (3–93) were required to identify 20% or 50% decreases in the size of the SMBC of contaminated soil samples relative to their uncontaminated control samples at the 0.05% level of statistical significance. We question the value of the routine measurement of SMBC as an ecotoxicological endpoint at the field scale, and suggest more robust and predictive microbiological indicators.