Search

This study investigated the carbon (C) and nitrogen (N) gas emissions (N2O, NH3, CO2 and CH4) from solid pig manure management in China. Gas emissions were quantified from static piles over 60 days during summer in China's Yangtze River Basin, using Drager-Tube and static chamber-gas chromatography techniques. High emissions of NH3 and N2O were observed at the early stage of storage, but high emission of CH4 occured later during storage. Overall, 62% of the total C in the original pile was lost; CO2 and CH4 emissions accounted for 57 and 0.2% of C lost respectively. Over the same time, 41% of the total N in the original pile was lost; NH3 and N2O emissions accounted for 15 and 0.3% of N lost respectively. The volatilization of NH3 during storage in summer was 4.56 g NH3 per kg dry weight. The total greenhouse gas (GHG) emissions during storage accounted for 67.93 g CO2 equivalent per kg dry weight; N2O and CH4 contributed to 46 and 55% of total GHG emissions respectively. Given China's major role in pig production, further attention should given to pig manure management to mitigate its contribution to atmospheric pollution.

Recent studies demonstrated that lignite application in feedlot can mitigate ammonia (NH3) emission from intensive livestock production, which is an important source of environmental pollution. However, the use of lignite on feedlot requires mining and transport of lignite, which are themselves sources of greenhouse gas and other gaseous pollutants. There is a need for an integrated assessment on the gas emissions to determine the potential impact of those additions to the production chain. Using a case study in Victoria, Australia, carbon dioxide (CO2) and NH3 were identified as key emission changes compared to business as usual (BAU). Social costs and benefits analysis indicated that these changes in emissions translate to social benefits of AUD$11 - $151 and $18 - $256 per cattle per year at lignite application rate of 3 and 6 kg m-2 respectively, while the corresponding social costs of the additional gaseous emissions are AUD$2 - $19 and $3 - $28 per cattle per year per 200 km. Our results indicate that the use of lignite in feedlot to mitigate NH3 can be targeted at feedlots located in proximity to lignite source, population centre and/or vulnerable ecosystems to maximise social benefits and minimise social costs. More broadly, estimating the social costs and benefits of changing manure management practice to mitigate NH3 emission generates information that can be used to evaluate alternative policies for N management.

Reactive nitrogen (Nr; all species of nitrogen other than N2 gas) is a major cause of air and water pollution, with worldwide costs of billions in human health and ecosystem damages. The nitrogen (N) footprint, which quantifies the anthropogenic release of Nr from the production and consumption of both food and energy, has been used as an indicator of sustainability at individual and national levels. Here, we present the first institutional N footprint in Australia – the N footprint for The University of Melbourne (UoM) in 2015, and projections to 2020 under four scenario families. The total N footprint of UoM in 2015 was 139 tonnes N; food production (36.7%), utilities (32.4%), and transport (28.1%) were the major contributors while food consumption and fertilizer usage made up the remaining 2.8%. Under a businessasusual scenario, the N footprint of UoM would grow by 13% to 157 tonnes N in 2020 due to increase in student and staff population and infrastructure development. However, UoM has the potential to reduce its N footprint by 59% relative to the 2015 baseline if it implements changes to food purchases and energy use by 2020. The mitigation strategies with the largest potential reduction should be prioritized, including shifting purchased electricity fuel sources to wind or solar (26% reduction) and reducing air travel emissions (25% reduction). We demonstrate the potential of the N footprint as a tool for an institution to assess and monitor the sustainability of its operations and governance. Universities are leading the way in sustainable development, and the calculation of N footprint for UoM is the starting point for future work on sustainable institutional Nr management in Australia.

The potential effect of herbicides on soil functions, including nitrogen (N) transformations, is of interest to farmers, advisers, regulators and the community, yet comparisons of herbicides with different modes of action in a range of soil types are scarce. We applied seven commonly used herbicides (glyphosate acid, 2,4-dichlorophenoxyacetic acid [2,4-D], metsulfuron-methyl, trifluralin, diuron, atrazine and diflufenican) and one fungicide (tebuconazole) to five different Australian cropping soils at a recommended and five times recommended rate. Mineral N levels and the activities of eight enzymes involved organic matter cycling, including β-N-acetylglucosaminidase and leucine aminopeptidase contributing to organic N transformation, were monitored over a 28-d period. Only one herbicide (atrazine) at a recommended rate statistically (P 25% inhibition cf. control treatment) reduced NO3− formation in one soil type at the end of the incubation. The remaining herbicides at recommended rates had inconsistent, transitory or negligible effects on enzyme activities and mineral N levels. However, five times the recommended rate of metsulfuron-methyl or 2,4-D caused alterations to mineral N levels, either as reduced NO3− or increased NH4+, across multiple soil types. This study suggests that N-transformation assays were at least, if not, more sensitive to herbicides than enzyme assays. Overall, our study confirms that single recommended rate applications of herbicides typically have limited effects on soil functions such as N-transformation and soil enzyme activities involved in organic matter and nutrient cycling. The observation of significant effects at higher-than-label rates highlights the need to follow label instructions and prevent herbicide accumulation in soil.

Microplastics and nanoplastics are emerging pollutants of global importance. They are small enough to be ingested by a wide range of organisms and at nano-scale, they may cross some biological barriers. However, our understanding of their ecological impact on the terrestrial environment is limited. Plastic particle loading in agroecosystems could be high due to inputs of some recycled organic waste and plastic film mulching, so it is vital that we develop a greater understanding of any potentially harmful or adverse impacts of these pollutants to agroecosystems. In this article, we discuss the sources of plastic particles in agroecosystems, the mechanisms, constraints and dynamic behaviour of plastic during aging on land, and explore the responses of soil organisms and plants at different levels of biological organisation to plastic particles of micro and nano-scale. Based on limited evidence at this point and understanding that the lack of evidence of ecological impact from microplastic and nanoplastic in agroecosystems does not equate to the evidence of absence, we propose considerations for addressing the gaps in knowledge so that we can adequately safeguard world food supply.

Plastic pollution is a global concern given its prevalence in aquatic and terrestrial ecosystems. Studies have been conducted on the distribution and impact of plastic pollution in marine ecosystems, but little is known on terrestrial ecosystems. Plastic mulch has been widely used to increase crop yields worldwide, yet the impact of plastic residues in cropland soils to soil health and crop production in the long term remained unclear. In this paper, using a global meta-analysis, we found that the use of plastic mulch can indeed increase crop yields on average by 25%-42% in the immediate season due to the increase of soil temperature (+8%) and moisture (+17%). However, the unabated accumulation of film residues in the field negatively impacts its physicochemical properties linked to healthy soil and threatens food production in the long term. It has multiple negative impacts on plant growth including crop yield (at the mean rate of -3% for every additional 100 kg/ha of film residue), plant height (-2%) and root weight (-5%), and soil properties including soil water evaporation capacity (-2%), soil water infiltration rate (-8%), soil organic matter (-0.8%) and soil available phosphorus (-5%) based on meta-regression. Using a nationwide field survey of China, the largest user of plastic mulch worldwide, we found that plastic residue accumulation in cropland soils has reached 550,800 tonnes, with an estimated 6%-10% reduction in cotton yield in some polluted sites based on current level of plastic residue content. Immediate actions should be taken to ensure the recovery of plastic film mulch and limit further increase in film residue loading to maintain the sustainability of these croplands.

The impact of microplastic pollution on terrestrial biota is an emerging research area, and this is particularly so for soil biota. In this study, we addressed this knowledge gap by examining the impact of aged low-density polyethylene (LDPE) and polyester fibres (i.e. polyethylene terephthalate, PET) on a forest microbiome composition and activity. We also measured the corresponding physicochemical changes in the soil. We observed that bacteria community composition diverged in PET and LDPE treated soils from that of the control by day 42. These changes occurred at 0.2% and 0.4% (w/w) of PET and at 3% LDPE. Additionally, soil respiration was 8-fold higher in soil that received 3% LDPE compared to other treatments and control. There were no clear patterns linking these biological changes to physicochemical changes measured. Taken together, we concluded that microplastics aging in the environment may have evolutionary consequences for forest soil microbiome and there is immediate implication for climate change if the observed increase in soil respiration is reproducible in multiple ecosystems.

Today's ecosystems are influenced by different factors that could evolve into stressors. Effects of pesticides, especially in agricultural areas, may interact with environmental factors, such as soil moisture fluctuation caused by global climate change. In this contribution, two semi-field studies conducted in Germany and Portugal with terrestrial model ecosystems are presented. Their aim was to assess the effects of the fungicide pyrimethanil under different soil moisture levels on Enchytraeidae. In Portugal a no observed effect concentration design was chosen, using two concentration levels: the maximum application rate (MAR) according to the safe use registration within the European Union and five times the MAR (1.82 and 9.09 mg/kg dry soil, respectively). Both concentrations did neither affect the total enchytraeid abundance nor single populations. In Germany an ECx design (effect concentration) was conducted, using 11 concentrations. In general, 14 EC50 values for different combinations of single species, moisture level and sampling date were determined. The strongest effects were found in dry soil, particularly for Fridericia connata (EC50: 3.48 mg/kg dry soil after 8 weeks of exposure). The advantages and challenges of these test designs are discussed with regard to the registration process of pesticides in the European Union. In any case, enchytraeids are suitable test organisms in such higher tier studies for the combined evaluation of chemical and climatic stressors due to their usually high diversity and abundances and their close contact with the soil solution.

The transformation of organic matter amendments in the soil is regulated by soil microbial communities. We examined the utility of ecological and functional stoichiometry theories to explain microbial transformation of organic amendments in the soil and examined the key relationships between soil microbial community composition, biomass and activity with resource elemental composition (soil and organic input) and nutrient availability. Using two contrasting soils amended with raw green waste, its compost or biochar, we found that microbial PLFA composition was distinct for each soil and organic amendment. Microbial activity was strongly influenced by organic amendment. Further, we observed that changes in the soil stoichiometry with inputs were accompanied by changes in total PLFA and bacteria: fungal ratio, but the relationships between them were inconsistent and changed over time. Microbial activities involved in C, N and P cycling were generally correlated, but the relationship between hydrolase β-glucosidase (BGL) and microbial N and P activities was stronger and more consistent than that between oxidases (phenol oxidase PPO, peroxidase POX) and microbial N and P activities. These microbial activity relationships translated to a consistent relationship between log(BGL):log(nutrient) and soil C:nutrient but a weaker and inconsistent relationship between log(PPO + POX):log(nutrient) and soil C:nutrient. Our analyses indicate that microbial composition can be different, but stoichiometric invariance of microbial activity constrained microbial community response to organic input.

Soil is central to human wellbeing through its provision of critical ecosystem services, including food and clean water. These services emerge through the self-organising nature of the soil system. Here, we consider the lessons learnt from the evolution of the understanding of human and ecosystem health for the conceptualisation and application of soil health. We share the fundamental and practical challenges of managing the land with respect to soil health, and the need for policy to drive the protection of soil as one of our most important non-renewable natural resources.