•The meta-analysis included 38 studies (422N2O emission factors in 12 countries).•The weighted-REML showed higher synthetic-N emission factors with better N2O coverage.•We propose a global emission ...factor for organic inputs of 0.57±0.3% of N applied.•We encourage the use of three identified N2O risk classes of organic amendments.•Emission factors were 2.8 times greater in fine- than in coarse-textured soils.
Agricultural soils receiving synthetic fertilizers and organic amendments containing nitrogen contribute a large part to anthropogenic nitrous oxide (N2O) emissions. As a source of nitrate that undergoes reduction to N2O, organic amendments also change soil C availability and redox potential, which influences the N2O emission factor (EF) of organically-amended soils. The objective of this study was to conduct a meta-analysis of N2O EF from agricultural soils receiving organic amendments. A global survey of peer-reviewed literature resulted in the selection of 38 studies including 422 observations at 43 sites in 12 countries. The analysis yielded a global EF for all organic sources, EForg, equal to 0.57±0.30%, which is lower than the IPCC default EF of 1 for synthetic fertilizers. Three groups of organic amendments with similar EFs were identified: the high-risk group including animal slurries, waste waters and biosolids (1.21±0.14%); the medium-risk group including solid manure, composts+fertilizers, and crop residues+fertilizers (0.35±0.13%); and the low-risk group including composts, crop residues, paper mill sludge and pellets (0.02±0.13%). The EF was higher when soils received organic amendments in combination with synthetic fertilizers, such as liquid manures+fertilizers (2.14±0.53%), composts+fertilizers (0.37±0.24%), and crop residues+fertilizers (0.59±0.27%). The EF was modulated by amendment (C/N ratio), soil (texture, drainage, organic C and N) and climatic (precipitation) factors. For example, EFs were on average 2.8 times greater in fine-textured than coarse-textured soils. We recommend site-specific EFs that consider organic amendment chemistry, soil characteristics, climate conditions and whether the organic amendment is applied alone or in combination with synthetic fertilizers.
Microcystins are cyanotoxins produced by many species of cyanobacteria. They are specific inhibitors of serine/threonine protein phosphatases and are phytotoxic to agricultural plants. This study ...used a formal meta-analysis to estimate the phytotoxicity and bioconcentration rates of agricultural plants exposed to microcystins, and the human health risk from consuming microcystin-contaminated plants. Among the 35 agricultural plants investigated, microcystins were most phytotoxic to durum wheat, corn, white mustard and garden cress. Leafy vegetables such as dill, parsley and cabbage could bioconcentrate ∼3 times more microcystins in their edible parts than other agricultural plants. Although the human health risk from ingesting microcystins could be greater for leafy vegetables than other agricultural plants, further work is needed to confirm bioconcentration of microcystins in realistic water-soil-plant environments. Still, we should avoid growing leafy vegetables, durum wheat and corn on agricultural land that is irrigated with microcystins-contaminated water and be attentive to the risk of microcystins contamination in the agricultural food supply.
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•Microcystins phytotoxicity in agricultural plants was studied by meta-analysis.•Greater phytotoxicity of microcystins is from natural bloom extract.•Durum wheat, corn, white mustard and garden cress exhibited the most phytotoxicity.•Leafy vegetables could bioconcentrate ∼3 times more microcystins than other plants.•Human health risk from ingesting microcystins could be greater for leafy vegetables.
Human ingestion of agricultural plants that bioconcentrate microcystins from contaminated irrigation water is an emerging public health issue.
•Biochar creates habitat and alters the soil environment for microorganisms.•Rapid change in microbial community structure and function after biochar application.•Long-term shifts in microbial ...communities depend on biochar source and soil texture.•Microorganisms are more sensitive to biochar source in sandy than clayey soils.
Soil microbial communities are responsive to biochar amendments. As the residence time of biochar in soil is expected to be hundreds to thousands of years, the changes in microbial community structure and functions could persist for a long period of time. Given that biochar is being applied as a soil amendment in many parts of the world, the long-term consequences for soil microbial communities need to be considered. The objective of this review is to document how biochar creates new habitats and changes the soil environment for microorganisms, which may lead to changes in microbial abundance, community structure and activities. Our meta-analysis revealed that slow pyrolyzed biochars produced from various feedstocks at temperatures from 300°C to 600°C consistently increased some physico-chemical properties (i.e., pH, cation exchange capacity and aggregation) and microbial parameters (i.e., abundance and community structure of microorganisms) in a vast number of soils during short (≤90days) laboratory incubations and longer (1–3years) field studies. The biochar-mediated changes in soil physico-chemical and biological properties appeared to be a function of soil texture and biochar type based on its feedstock and production temperature, which determines key biochar characteristics such as surface area, porosity and pH. Biochars derived from manure or crop residue feedstocks tend to promote microbial abundance more than wood-derived biochars. Biochars derived from wood and other lignocellulosic-rich feedstocks tend to exhibit beneficial effects on soil microbial abundance later (≥60days) than biochars from manure or crop residue feedstocks. Coarse textured soils tend to have less aggregation, lower microbial biomass and lower enzyme activities when amended with slow pyrolyzed biochars produced at high temperatures (>600°C), but these biochars did not affect the physico-chemical and biological properties of clayey soils. Further research is needed to evaluate the magnitude of biochar influence on soil microbial abundance and activities considering (1) the biochar particle size, surface area, porosity, nutrient content and pH, and (2) the soil organic matter (SOM) content and microbial abundance of the soil matrix. Once the microbial activities in the biochar–soil system are understood, they can be manipulated through organic and inorganic fertilizer applications to sustain or improve agricultural crop production.
Biochar application is perceived as a promising agricultural technology, but risk evaluation on the soil ecosystem has focused exclusively on soil microbes, whether microfood-web is likewise ...influenced by biochar remains unclear. We carried out a pot experiment planted with rapeseed for 2 years to test how biochar application (0, 20, 60 t ha
−1
), with or without nitrogen (N) fertilizer (0, 60, 120 t ha
−1
), affected soil microbes and microfauna (protists and nematodes). We observed that a high amount of biochar (60 t ha
−1
) increased crop productivity, microbial activity, and biomass carbon (C) and N, as well as the abundance of flagellates (protists), but decreased the abundances of bacterivorous, fungivorous, and herbivorous nematodes as well as the abundance of amoebae (protists). High biochar addition rates also shifted nematode community composition toward a fungivore dominance, and favored herbivores by decreasing the ratio of microbivorous to herbivorous nematodes. However, N fertilizer and its interaction with biochar generally had no effect on microbial activity and biomass as well as the abundance of protist and nematode. A structural equation model revealed that the effects of biochar on soil biota were largely direct, which might depend on biochar properties (e.g., pore size and alkalinity), whereas indirect effects, mediated by crop, soil pH, soil moisture, and polycyclic aromatic hydrocarbon (PAH) concentration, generally had no effect on soil biota. We conclude that biochar is a suitable soil amendment for increasing crop growth, but its detrimental effect on multitrophic levels of soil fauna calls for an identification of the optimal application rate and size fraction that could minimize potential negative effects on certain soil communities.
Climate change is expected to negatively affect production of winter wheat and maize in the North China Plain (NCP). This study examines the perceptions and adaptations to climate change of farmers ...in Quzhou County in the NCP. Structured interviews were held with 37 smallholder farmers to determine their perceptions of and adaptations to climate change in the past 30 yr. Historical meteorological data (1980 to 2010) showed a significant increase in mean annual temperature of 1.7°C over 30 yr and no significant change in mean annual rainfall, but farmers perceive increasing temperature and decreasing rainfall during this period. We hypothesize that this leads farmers to irrigate more, due to their perception that the changing temperature and precipitation regime is increasing crop water stress. Further increase in annual temperature predicted for the NCP will intensify irrigation and deplete the groundwater reserves used for irrigation in this area. Farmers in the NCP require decision-making tools to develop sustainable irrigation practices for long-term adaptation to climate change.
Low molecular weight organic acids exuded by plants roots enhance inorganic Pᵢ release into soil solution and thereby increases plant‐available Pi in soils. Low molecular weight organic acids may ...also induce organic P (Pₒ) release into soil solution, but kinetics of both Pi and Po displacement from the soil matrix into soil solution of agricultural soils is poorly understood, and the mechanism for Pₒ release is not well explained. This study used kinetic experiments to determine the concentrations and release rates of Pᵢ and Pₒ induced by oxalic acid, citric acid, and malic acid in calcareous, neutral and acidic soils. Kinetic data were well described by Elovich (r² = 0.801–0.993, P < 0.001) and power functions models (r² = 0.721–0.977, P < 0.001). Low molecular weight organic acids at 10 mmol kg⁻¹ soil induced the exponential release of both Pᵢ and Pₒ, which reached a plateau approx. 480– 2,880 min after the start of the experiment. Cumulative Pₒ release induced by low molecular weight organic acids was ranked as oxalic acid (0.63–3.17 mg kg⁻¹) > citric acid (0.61–2.82 mg kg⁻¹) > malic acid (0.52–1.76 mg kg⁻¹) and mainly resulted from the release of labile Pₒ (NaHCO₃‐Pₒ) regardless of soil type. By contrast, oxalic acid was most effective in enhancing Pᵢ release from the HCl‐Pᵢ (Ca‐Pᵢ) fraction of the calcareous soil, and citric acid was most effective in releasing Pᵢ from the NaOH‐Pᵢ (Fe/Al‐Pᵢ) fraction of the neutral and acidic soils. Therefore, the mechanism for the kinetics of Pₒ release induced by low molecular weight organic acids is ascribed to their ability to mobilize the labile Pₒ (NaHCO₃‐Pₒ) rather than their ability to chelate cations (i.e., Fe³⁺, Al³⁺) bound to Pₒ in soil.
Agricultural management practices that alter the soil organic matter (SOM) content are expected to cause changes in soil stability and aggregation. Animal manure is a source of organic matter (OM) ...that has been demonstrated to increase macroaggregate formation and stability. The objectives of this study were to determine how long term cattle manure applications to a calcareous Haploboroll clay loam (Lethbridge, AB, Canada) affected aggregate size distribution, the total C, N, and P content of aggregate size fractions, and water‐stable aggregates. Beef cattle manure applied at rates >30 Mg ha−1 yr−1 under dryland production and >60 Mg ha−1 yr−1 to soils under irrigation resulted in fewer dry‐sieved aggregates >7.1 mm and more dry‐sieved aggregates between 0.47 and 1.2 mm in the 0‐ to 5‐cm depth, compared with unamended soils. The dry‐sieved aggregate fractions between 0.47 and 1.2 mm include the <0.84‐mm fraction that has been associated with increased susceptibility to wind erosion in the Canadian semiarid prairies. There was more total C, N, and P in all dry‐sieved aggregate fractions of soils receiving >30 Mg manure ha−1 yr−1 than unamended soils, and dry‐sieved aggregates between 0.47 and 2.0 mm tended to have the highest C, N, and P contents. Water aggregate stability was higher in irrigated than dryland soils, but did not improve with increasing manure application rates. Dispersing agents in the cattle manure appear to have destabilized the larger soil macroaggregates.
Among factors controlling decomposition and retention of residue C in soil, effect of initial soil organic C (SOC) concentration remains unclear. We evaluated, under controlled conditions, short-term ...retention of corn residue C and total soil CO
2
production in C-rich topsoil and C-poor subsoil samples of heavy clay. Topsoil (0–20 cm deep, 31.3 g SOC kg
−1
soil) and subsoil (30–70 cm deep, 4.5 g SOC kg
−1
soil) were mixed separately with
13
C–
15
N-labeled corn (
Zea mays
L.) residue at rates of 0 to 40 g residue C kg
−1
soil and incubated for 51 days. We measured soil CO
2
–C production and the retention of residue C in the whole soil and the fine particle-size fraction (<50 μm). Cumulative C mineralization was always greater in topsoil than subsoil. Whole-soil residue C retention was similar in topsoil and subsoil at rates up to 20 g residue C kg
−1
. There was more residue C retained in the fine fraction of topsoil than subsoil at low residue input levels (2.5 and 5 g residue C kg
−1
), but the trend was reversed with high residue inputs (20 and 40 g residue C kg
−1
). Initial SOC concentration affected residue C retention in the fine fraction but not in the whole soil. At low residue input levels, greater microbial activity in topsoil resulted in greater residue fragmentation and more residue C retained in the fine fraction, compared to the subsoil. At high residue input levels, less residue C accumulated in the fine fraction of topsoil than subsoil likely due to greater C saturation in the topsoil. We conclude that SOC-poor soils receiving high C inputs have greater potential to accumulate C in stable forms than SOC-rich soils.
Spatial variability in carbon dioxide (CO
2), nitrous oxide (N
2O) and methane (CH
4) emissions from soil is related to the distribution of microsites where these gases are produced. Porous soil ...aggregates may possess aerobic and anaerobic microsites, depending on the water content of pores. The purpose of this study was to determine how production of CO
2, N
2O and CH
4 was affected by aggregate size and soil water content. An air-dry sandy loam soil was sieved to generate three aggregate fractions (<0.25
mm, 0.25–2
mm and 2–6
mm) and bulk soil (<2
mm). Aggregate fractions and bulk soil were moistened (60% water-filled pore space, WFPS) and pre-incubated to restore microbial activity, then gradually dried or moistened to 20%, 40%, 60% or 80% WFPS and incubated at 25
°C for 48
h. Soil respiration peaked at 40% WFPS, presumably because this was the optimum level for heterotrophic microorganisms, and at 80% WFPS, which corresponded to the peak N
2O production. More CO
2 was produced by microaggregates (<0.25
mm) than macroaggregate (>0.25
mm) fractions. Incubation of aggregate fractions and soil at 80% WFPS with acetylene (10
Pa and 10
kPa) and without acetylene showed that denitrification was responsible for 95% of N
2O production from microaggregates, while nitrification accounted for 97–99% of the N
2O produced by macroaggregates and bulk soil. This suggests that oxygen (O
2) diffusion into and around microaggregates was constrained, whereas macroaggregates remained aerobic at 80% WFPS. Methane consumption and production were measured in aggregates, reaching 1.1–6.4
ng
CH
4–C
kg
−1
soil
h
−1 as aggregate fractions and soil became wetter. For the sandy-loam soil studied, we conclude that nitrification in aerobic microsites contributed importantly to total N
2O production, even when the soil water content permitted denitrification and CH
4 production in anaerobic microsites. The relevance of these findings to microbial processes controlling N
2O production at the field scale remains to be confirmed.
•Cyanobacteria, diatoms and dinoflagellates blooms can synthesize cyanotoxins.•The successive presence of cyanotoxins may pose chronic toxicity.•Abiotic-biotic factors that affected seasonal shifts ...of algal species were documented.•Multiple ecological roles and physiological functions of cyanotoxins were evaluated.•Human and ecological health risks of harmful algal blooms were illustrated.
Human and ecological health depends on the vitality of freshwater systems, but these are increasingly threatened by cyanotoxins released from harmful algal blooms (HABs). Periodic cyanotoxin production, although undesirable, may be tolerable when there is enough time for cyanotoxins to degrade and dissipate in the environment, but the year-round presence of these toxins will be a chronic health for humans and ecosystems. The purpose of this critical review is to document the seasonal shifts of algal species and their ecophysiological acclimatation to dynamic environmental conditions. We discuss how these conditions will create successive occurrences of algal blooms and the release of cyanotoxins into freshwater. We first review the most common cyanotoxins, and evaluate the multiple ecological roles and physiological functions of these toxins for algae. Then, the annual recurring patterns HABs are considered in the context of global change, which demonstrates the capacity for algal blooms to shift from seasonal to year-round growth regimes that are driven by abiotic and biotic factors, leading to chronic loading of freshwaters with cyanotoxins. At last, we illustrate the impacts of HABs on the environment by compiling four health issues and four ecology issues emanating from their presence in the that covers atmosphere, aquatic ecosystems and terrestrial ecosystems. Our study highlights the annual patterns of algal blooms, and proposes that a “perfect storm” of events is lurking that will cause the ‘seasonal toxicity’ to become a full-blown, ‘chronic toxicity’ in the context of the deterioration of HABs, highlighting a non-negligible chronic health and ecological hazard.
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