Imazapic and diuron availability and toxicity in different soils

Take home message • Herbicide residue levels can be measured in soil, but to interpret what soil analysis results mean for the subsequent crop, information about crop toxicity thresholds, and soil-specific herbicide availability is needed. • An approach has been developed to derive toxicity thresholds and predict herbicide availability in different soils to provide a prediction of safety for cropping. • Soil analysis for herbicide residues is not a replacement for using herbicides according to label requirements. • Additional ground truthing of this proof-of-concept research across a wider range of soil types and environments will strengthen the predictions

Management of Pasture Soils: Biochar Stability, Carbon Storage Potential and Its Effect on Production and Quality

The use of biochar has been proposed as a stable carbon (C) amendment with long-term carbon (C) storage potential in agricultural soils while improving primary productivity. However, this concept has not been widely tested in contrasting soils under temperate pasture systems. To address this knowledge gap, a 13C-labelled biochar, produced from Eucalyptus saligna biomass by slow pyrolysis (450° C; d13C -36.7‰) was surface (0 10 cm) applied in C3 dominated, annual temperate pasture systems across Arenosol, Cambisol and Ferralsol. The results show that only 2% of the applied biochar-C was mineralised in a relatively clay- and C-poor Arenosol, 4.6% in a clay- and C-rich Cambisol, and 7% in a clay- and C-rich and earthworm-abundant Ferralsol over 12 months. Biochar application increased soil C stock, while the mean residence time of biochar-C, an indicator of its stability in soil, decreased with increasing native C content and/or pasture productivity across the soils i.e. Arenosol (71 years) \u3c Cambisol (39 years) \u3c Ferralsol (29 years). Biochar application increased pasture growth rate only on two occasions over 12 months in the Ferralsol but not in the other pasture-soil systems. The biochar-C recovery to 12 30 cm depth varied as 1.2% (Arenosol), 2.7% (Cambisol) and 15.7% (Ferralsol) after 12 months. Cumulative CO2-C emission from native soil-plant sources was lower (p \u3c 0.10) in the biochar-amended vs. non-amended Ferralsol. This study shows that the downward migration of biochar-C exceeded its loss via mineralisation in the Arenosol and Ferralsol but in the Cambisol. This migration of biochar to deeper soil layers could enhance C sequestration potential in soil systems

Real-time forecasting of pesticide concentrations in soil

peer-reviewedForecasting pesticide residues in soils in real time is essential for agronomic purposes, to manage phytotoxic effects, and in catchments to manage surface and ground water quality. This has not been possible in the past due to both modelling and measurement constraints. Here, the analytical transient probability distribution (pdf) of pesticide concentrations is derived. The pdf results from the random ways in which rain events occur after pesticide application. First-order degradation kinetics and linear equilibrium sorption are assumed. The analytical pdfs allow understanding of the relative contributions that climate (mean storm depth and mean rainfall event frequency) and chemical (sorption and degradation) properties have on the variability of soil concentrations into the future. We demonstrated the two uncertain reaction parameters can be constrained using Bayesian methods. An approach to a Bayesian informed forecast is then presented. With the use of new rapid tests capable of providing quantitative measurements of soil concentrations in the field, real-time forecasting of future pesticide concentrations now looks possible for the first time. Such an approach offers new means to manage crops, soils and water quality, and may be extended to other classes of pesticides for ecological risk assessment purposes

Effects of crabs on greenhouse gas emissions, soil nutrients, and stoichiometry in a subtropical estuarine wetland 260 __

Crabs may elicit effects on wetland carbon (C), nitrogen (N), and phosphorus (P) concentrations and associated ecological stoichiometry. In this study, we assessed effects of crabs on carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) emissions; soil C, N, and P concentrations; and stoichiometry in upper and mid-tidal flats of an estuarine wetland in China. The results showed that averaged CO2, CH4, and N2O fluxes were greater in the upper and mid-tidal flats in the presence of crabs, being 46.4, 66.7, and 69.7% and 53.6, 143, and 73.1% greater than control, respectively. Mixed model analyses showed overall positive relationships between wetland soil CO2 CH4 and N2O emissions (F = 4.65, P = 0.033; F = 42.42, P = 0.042 and F = 10.2, P = 0.0018, respectively) in the presence of crabs, taking into account season, flooding intensity, and plot effects. This may be related to the direct effects of respiration and the indirect effects of feeding, excretion, and disturbance of soil on microorganisms and/or plant roots. There were no effects of crabs on total C or N concentrations, whereas decreased soil total P concentrations, especially in the upper-tidal flats (P = 0.04). Crab presence was positively associated with soil C/P and N/P ratios (P < 0.0001 and P < 0.0001, respectively), taking into account season, flooding intensity, and plot effects. In the upper and mid-tidal flats, soil CO2 emissions were negatively correlated with total soil C; CH4 emissions were positively correlated with ratios of C/N and C/P; and N2O emissions were positively correlated with N content. In general, global warming potential (GWP) of the upper-tidal flats in the presence of crabs increased by 138% compared with the absence of crabs, and GWP of the mid-tidal flats in the presence of crabs increased by 99.3% compared with the absence of crabs. Global warming and associated flooding rise in several coastal wetland areas are favoring benthic fauna number enhancement, and this in turn increases GWP of overall gas emissions further contributing to future warming rise

Biochar-based fertilizer: Supercharging root membrane potential and biomass yield of rice

Biochar-based compound fertilizers (BCF) and amendments have proven to enhance crop yields and modify soil properties (pH, nutrients, organic matter, structure etc.) and are now in commercial production in China. While there is a good understanding of the changes in soil properties following biochar addition, the interactions within the rhizosphere remain largely unstudied, with benefits to yield observed beyond the changes in soil properties alone. We investigated the rhizosphere interactions following the addition of an activated wheat straw BCF at an application rates of 0.25% (g·g−1 soil), which could potentially explain the increase of plant biomass (by 67%), herbage N (by 40%) and P (by 46%) uptake in the rice plants grown in the BCF-treated soil, compared to the rice plants grown in the soil with conventional fertilizer alone. Examination of the roots revealed that micron and submicron-sized biochar were embedded in the plaque layer. BCF increased soil Eh by 85 mV and increased the potential difference between the rhizosphere soil and the root membrane by 65 mV. This increased potential difference lowered the free energy required for root nutrient accumulation, potentially explaining greater plant nutrient content and biomass. We also demonstrate an increased abundance of plant-growth promoting bacteria and fungi in the rhizosphere. We suggest that the redox properties of the biochar cause major changes in electron status of rhizosphere soils that drive the observed agronomic benefits

A critical review of methods for analyzing freshwater eutrophication

Water eutrophication is a global environmental problem that poses serious threats to aquatic ecosystems and human health. The evaluation of eutrophication provides a theoretical basis and technical guidance for the management and rehabilitation of water ecosystems. In the last four decades, dozens of evaluation methods have been applied to freshwater eutrophication, but there is a clear need to optimize and standardize the most suitable methods. We have addressed this gap by presenting a systematic review of methodologies. Due to the diversity and complexity of water bodies, no single evaluation method was identified that would adequately represent eutrophication under all scenarios. We demonstrate that lakes can best be assessed using the trophic level index (TLI) method, reservoirs and wetlands the trophic state index (TSI) and fuzzy comprehensive evaluation (FCE) method, respectively, and rivers the FCE method or back propagation (BP) neural network methods. More recently applied methodologies including spectral imaging and 3-D mapping of water quality using underwater gliders allow greater resolution and can be effective in managing waterbodies to avoid future eutrophication. The aim of this review is to guide future studies on the most appropriate methods available for assessing and reporting water eutrophication

A communal catalogue reveals Earth's multiscale microbial diversity

Our growing awareness of the microbial world's importance and diversity contrasts starkly with our limited understanding of its fundamental structure. Despite recent advances in DNA sequencing, a lack of standardized protocols and common analytical frameworks impedes comparisons among studies, hindering the development of global inferences about microbial life on Earth. Here we present a meta-analysis of microbial community samples collected by hundreds of researchers for the Earth Microbiome Project. Coordinated protocols and new analytical methods, particularly the use of exact sequences instead of clustered operational taxonomic units, enable bacterial and archaeal ribosomal RNA gene sequences to be followed across multiple studies and allow us to explore patterns of diversity at an unprecedented scale. The result is both a reference database giving global context to DNA sequence data and a framework for incorporating data from future studies, fostering increasingly complete characterization of Earth's microbial diversity.Peer reviewe

A communal catalogue reveals Earth’s multiscale microbial diversity

Our growing awareness of the microbial world’s importance and diversity contrasts starkly with our limited understanding of its fundamental structure. Despite recent advances in DNA sequencing, a lack of standardized protocols and common analytical frameworks impedes comparisons among studies, hindering the development of global inferences about microbial life on Earth. Here we present a meta-analysis of microbial community samples collected by hundreds of researchers for the Earth Microbiome Project. Coordinated protocols and new analytical methods, particularly the use of exact sequences instead of clustered operational taxonomic units, enable bacterial and archaeal ribosomal RNA gene sequences to be followed across multiple studies and allow us to explore patterns of diversity at an unprecedented scale. The result is both a reference database giving global context to DNA sequence data and a framework for incorporating data from future studies, fostering increasingly complete characterization of Earth’s microbial diversity

Enhanced biodegradation of phenoxyacetate and triazine herbicides by plant-microbial rhizoplane associations and adapted soil microorganisms

Strategies for the enhanced biological degradation of pesticides were examined in this research project. In one approach, the concept of the plant—microbial rhizosphere association was investigated as a laboratory model using the herbicide 2,4-D as a test compound. In another, an enhanced degradation of the recalcitrant herbicide atrazine was shown. Here, two microbial populations each capable of rapid atrazine metabolism were studied. The metabolism of 2,4-D by bacteria associated with the root system of wheat and canola seedlings was demonstrated in this study using a hydroponic system as well as a solid medium of sand and gravel. Significant and rapid 2,4-D metabolism (near 100% within 24h) was found in all hydroponic systems where the 2,4-D degrading microorganisms, Acinetobacter baumannii pJP4 transconjugant, Alcaligenes eutrophus and Azospirillum brasilense pIP4 transconjugant were associated with the roots. The metabolism of 2,4-D by Azospirillum brasilense pJP4 transconjugant associated with wheat was less rapid than associations with the other 2,4-D degrading bacteria. There was little difference in the rates of degradation between the hydroponic system and the sand/gravel mixture. The colonisation of the roots of seedlings by microbes was studied by both fluorescence and laser scanning confocal microscopy. Colonisation was often prolific without favoured areas of attachment on the root. A pre-treatment of seedlings with a synthetic auxin which formed para-nodular structures had little effect on the nature of colonisation. Counts of colony forming units, however, established that there was an increase of an order in magnitude of cells per root system when the plants were pretreated with this synthetic auxin. An average of 5.5 x 106 viable cells of 2,4-D degrading Acinetobacter baumannii were counted on para-modulated wheat root systems. It was demonstrated that the colonisation of the rhizosphere by suitable microbes could protect canola seedlings against phytotoxic effects of the applied herbicide. Whether this bio-safening effect will be seen in solid media or in field situations with these nonleguminous plants was not investigated. Significant rates of atrazine degradation either in the laboratory or in the field have rarely been reported. Attempts were therefore made to obtain microbes capable of such metabolism. These attempts had the ultimate goal of providing microbes for application in the model plant microbial rhizosphere association. Two microbial cultures, each capable of rapid atrazine metabolism, were obtained and studies of the metabolic processes were conducted. Rhodococcus sp. NI86/21 metabolised atrazine within l44h to two N—dealkylated products, desisopropylatrazine and desethylatrazine. Mineralisation of the ethyl-14C labelled sidechain to 14CO; was demonstrated, accounting for 25% of the total applied label in the broth culture. Desisopropylatrazine was shown to be the major metabolite. Desethylatrazine was shown as a terminal metabolite in the degradation of atrazine by Rhodococcus sp. N186/21, accumulating in the broth. In other studies using it as the substrate, no firrther metabolism was found. Desisopropylatrazine was also indicated to have been a terminal metabolite as it too accumulated in the broth. The metabolism of prometryn, a thio-ester (non-chlorinated) s-triazine was also investigated in these studies. Although Rhodococcus Sp. N186/21 did not rapidly degrade prometryn under similar conditions to those used with the atrazine assays, a mono-N-dealkylated metabolite was identified by mass-spectrometry. Possibly, prometryn was toxic to the Rhodococcus at the concentration used (lOug mL'l), as only minimal growth of the bacteria in the broth was observed by increased absorbance. Such a toxic effect was likely to have inhibited the N-dealkylation metabolism of the prometryn. In another approach, soil from a pesticide sullage site on a farm in northern NSW was assayed for its atrazine metabolising ability. Although there was no initial activity, after 30 months of perfirsion of the soil with a concentrated solution of the herbicide, it had acquired the ability to rapidly mineralise atrazine. A rapid conversion of the three carbons in the s—triazine ring to C02 was demonstrated using radiolabelled atrazine. Also, the labelled carbon in the ethyl sidechain of atrazine was rapidly metabolised to CO2. The sidechain 14C label was mineralised to 14C02 at a slower rate than the carbons in the ring. It was demonstrated that there was a likelihood of the sidechain carbon being incorporated into an unextractable intermediate metabolite, which was subsequently also less susceptible to attack by the microorganisms. There were no significant metabolites of atrazine accumulated in the broth. The likely presence of hydroxyatrazine was noted in the assay using uniformly ring—labelled [14C] atrazine. Hydroxyatrazine was also identified in the assay with ethyl-sidechain labelled [14C] atrazine, however, the amount detected was less. The presence of atrazine at 25pg mL-l inhibited nitrification reactions in the soil, however, at a saturating concentration of SOug mL-l there was some ammonia oxidation noted. Attempts to isolate single bacterial colonies capable of the metabolism of atrazine were unsuccessful. Although there was insufficient time to utilise these microbial cultures in the plant microbial rhizosphere associations, studies on the metabolism of atrazine have sufficiently characterised the nature of biodegradation to suggest that plant-microbial associations can be confidently tested in fiiture experiments