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An understanding of the dynamics of soil organic carbon (SOC) as affected by farming practices is imperative for maintaining soil productivity and mitigating global warming. Results of a long-term (32 years) experiment in the Indian Himalayas under rainfed soybean (Glycine max L.)- wheat (Triticum aestivum L.) rotation was analyzed to determine the effects of mineral fertilizer and farmyard manure (FYM) application at 10 Mg ha⁻¹ on SOC stocks and depth distribution of the labile and recalcitrant pools of SOC. Results indicate all treatments increased SOC contents over the control. The annual application of NPK significantly (P < 0.05) enhanced total SOC, oxidizable soil organic C and its fractions over the control plots. The increase in these SOC fractions was greater with the NPK + FYM treatment. Nearly 16% (mean of all treatments) of the estimated added C was stabilized into SOC both in the labile and recalcitrant pools, preferentially in the 0-30 cm soil layer. However, the labile:recalcitrant SOC ratios of applied C stabilized was largest in the 15-30 cm soil layer. About 62% of total SOC was present in the labile pool. Plots under the N + FYM and NPK + FYM treatments contained a larger proportion of total SOC in the recalcitrant pool than the plots with mineral or no fertilizer, indicating that FYM application promoted SOC stabilization.

Antibiotic resistance genes (ARGs) are emerging contaminants posing a potential worldwide human health risk. Intensive animal husbandry is believed to be a major contributor to the increased environmental burden of ARGs. Despite the volume of antibiotics used in China, little information is available regarding the corresponding ARGs associated with animal farms. We assessed type and concentrations of ARGs at three stages of manure processing to land disposal at three large-scale (10,000 animals per year) commercial swine farms in China. In-feed or therapeutic antibiotics used on these farms include all major classes of antibiotics except vancomycins. High-capacity quantitative PCR arrays detected 149 unique resistance genes among all of the farm samples, the top 63 ARGs being enriched 192-fold (median) up to 28,000-fold (maximum) compared with their respective antibiotic-free manure or soil controls. Antibiotics and heavy metals used as feed supplements were elevated in the manures, suggesting the potential for coselection of resistance traits. The potential for horizontal transfer of ARGs because of transposon-specific ARGs is implicated by the enrichment of transposases—the top six alleles being enriched 189-fold (median) up to 90,000-fold in manure—as well as the high correlation (r ² = 0.96) between ARG and transposase abundance. In addition, abundance of ARGs correlated directly with antibiotic and metal concentrations, indicating their importance in selection of resistance genes. Diverse, abundant, and potentially mobile ARGs in farm samples suggest that unmonitored use of antibiotics and metals is causing the emergence and release of ARGs to the environment.

Nutrient pollution and greenhouse gas emissions related to crop agriculture and confined animal feeding operations (CAFOs) in the US have changed substantially in recent years, in amounts and forms. This review is intended to provide a broad view of how nutrient inputs—from fertilizer and CAFOs—as well as atmospheric NH 3 and greenhouse gas emissions, are changing regionally within the US and how these changes compare with nutrient inputs from human wastewater. Use of commercial nitrogen (N) fertilizer in the US, which now exceeds 12,000,000 metric tonnes (MT) continues to increase, at a rate of 60,000 MT per year, while that of phosphorus (P) has remained nearly constant over the past decade at around 1,800,000 MT. The number of CAFOs in the US has increased nearly 10% since 2012, driven largely by a near 13% increase in hog production. The annualized inventory of cattle, dairy cows, hogs, broiler chickens and turkeys is approximately 8.7 billion, but CAFOs are highly regionally concentrated by animal sector. Countrywide, N applied by fertilizer is about threefold greater than manure N inputs, but for P these inputs are more comparable. Total manure inputs now exceed 4,000,000 MT as N and 1,400,000 MT as P. For both N and P, inputs and proportions vary widely by US region. The waste from hog and dairy operations is mainly held in open lagoons that contribute to NH₃ and greenhouse gas (as CH₄ and N₂O) emissions. Emissions of NH 3 from animal waste in 2019 were estimated at [4,500,000 MT. Emissions of CH 4 from manure management increased 66 % from 1990 to 2017 (that from dairy increased 134 %, cattle 9.6 %, hogs 29 % and poultry 3 %), while those of N 2 O increased 34 % over the same time period (dairy 15 %, cattle 46 %, hogs 58 %, and poultry 14 %). Waste from CAFOs contribute substantially to nutrient pollution when spread on fields, often at higher N and P application rates than those of commercial fertilizer. Managing the runoff associated with fertilizer use has improved with best management practices, but reducing the growing waste from CAFO operations is essential if eutrophication and its effects on fresh and marine waters–namely hypoxia and harmful algal blooms (HABs)—are to be reduced.

International initiatives are emphasizing the capture of atmospheric CO2 in soil organic C (SOC) to reduce the climatic footprint from agroecosystems. One approach to quantify the contribution of management practices towards that goal is through analysis of long-term experiments (LTEs). Our objectives were to analyze knowledge gained in literature reviews on SOC changes in LTEs, to evaluate the results regarding interactions with pedo-climatological factors, and to discuss disparities among reviews in data selection criteria. We summarized mean response ratios (RRs) and stock change rate (SCR) effect size indices from twenty reviews using paired comparisons (N). The highest RRs were found with manure applications (30%, N = 418), followed by aboveground crop residue retention and the use of cover crops (9–10%, N = 995 and 129), while the effect of nitrogen fertilization was lowest (6%, N = 846). SCR for nitrogen fertilization exceeded that for aboveground crop residue retention (233 versus 117 kg C ha−1 year−1, N = 183 and 279) and was highest for manure applications and cover crops (409 and 331 kg C ha−1 year−1, N = 217 and 176). When data allows, we recommend calculating both RR and SCR because it improves the interpretation. Our synthesis shows that results are not always consistent among reviews and that interaction with texture and climate remain inconclusive. Selection criteria for study durations are highly variable, resulting in irregular conclusions for the effect of time on changes in SOC. We also discuss the relationships of SOC changes with yield and cropping systems, as well as conceptual problems when scaling-up results obtained from field studies to regional levels.

No fertilized soils (unfertilized and fallow treatments) and soils subjected to 28-year fertilization regimes, including mineral fertilization (PK and NPK) and manure amendments (NPKM and M), were incubated with or without 13C - glucose. Results showed that compared to mineral fertilization (0.64 − 0.69), the manure amendments significantly increased microbial C use efficiency (CUE) (0.76 − 0.79), mainly due to higher soil pH, lower resource stoichiometric ratios of dissolved organic C (DOC): mineral N, DOC: available P and mineral N: available P, and lower specific activities (per microbial biomass C unit) of β-1,4-glucosidase, N-acetyl-glucosaminidase and acid phosphatase. Glucose addition increased SOC mineralization, inducing positive priming effect (PE) with lower values in the manure amendments (0.11 − 0.12 mg C g−1 SOC) relative to mineral fertilization (0.25 − 0.55 mg C g−1 SOC). The PE was negatively correlated with soil pH and positively associated with resource stoichiometric ratios of DOC: mineral N, DOC: available P and mineral N: available P, mainly due to microbes mineralizing SOM to release nutrients, as indicated by the positive relationships between PE and the specific activities of N-acetyl-glucosaminidase and acid phosphatase. Concluding, relative to mineral fertilization, long-term manure amendment could increase CUE and decrease PE via alleviated soil acidification and resource limitation, thus facilitating soil C sequestration.

Ammonia (NH3) can interact in the atmosphere with other trace chemical species, which can lead to detrimental environmental consequences, such as the formation of fine particulates and ultimately global climate change. China is a major agricultural country, and livestock numbers and nitrogen fertilizer use have increased drastically since 1978, following the rapid economic and industrial development experienced by the country. In this study, comprehensive NH3 emissions inventories were compiled for China for 1980–2012. In a previous study, we parameterized emissions factors (EFs) considering ambient temperature, soil acidity, and the method and rate of fertilizer application. In this study, we refined these EFs by adding the effects of wind speed and new data from field experiments of NH3 flux in cropland in northern China. We found that total NH3 emissions in China increased from 5.9 to 11.1 Tg from 1980 to 1996, and then decreased to 9.7 Tg in 2012. The two major contributors were livestock manure and synthetic fertilizer application, which contributed 80–90 % of the total emissions. Emissions from livestock manure rose from 2.86 Tg (1980) to 6.16 Tg (2005), and then decreased to 5.0 Tg (2012); beef cattle were the largest source followed by laying hens and pigs. The remarkable downward trend in livestock emissions that occurred in 2007 was attributed to a decrease in the numbers of various livestock animals, including beef cattle, goats, and sheep. Meanwhile, emissions from synthetic fertilizer ranged from 2.1 Tg (1980) to 4.7 Tg (1996), and then declined to 2.8 Tg (2012). Urea and ammonium bicarbonate (ABC) dominated this category of emissions, and a decline in ABC application led to the decrease in emissions that took place from the mid-1990s onwards. High emissions were concentrated in eastern and southwestern China. Seasonally, peak NH3 emissions occurred in spring and summer. The inventories had a monthly temporal resolution and a spatial resolution of 1000 m, and thus are suitable for global and regional air-quality modeling.

Emissions of nitrous oxide (N2O), a potent greenhouse gas, from farmland have been recognized to be affected by soil pH and nitrogen (N) fertilizer application. However, the interactive effects of soil pH and N fertilizer type on N2O emissions and their influencing mechanism are poorly understood. A field experiment was conducted to elucidate the impacts of synthetic fertilizer and manure on soil properties and N2O fluxes along a soil acidity gradient (soil pH = 6.8, 6.1, 5.2, and 4.2) in the Huai River Basin, and a lab incubation experiment was performed to understand the underlying mechanisms of changed N2O flux. Low soil pH inhibited the ammonia-oxidizing bacteria abundance and thereby reduced the N2O production by nitrification under both synthetic fertilizer and manure application. The N2O production by denitrification was also reduced with declining soil pH, likely due to the decreased nirS and nirK abundances, and lower NO3−. However, low soil pH reduced the nosZ abundance and increased (nirS + nirK)/nosZ ratio, resulting in the increased N2O/(N2O + N2) ratio. Finally, with the decreased nitrification and denitrification, soil N2O emission was significantly reduced with declining soil pH regardless of fertilizer types. Compared with synthetic fertilizer, manure application increased soil nutrients (total N, dissolved organic C, and NO3−), nirK abundance, and (nirS + nirK)/nosZ ratio in the soils with pH of 5.2 and 4.2, thereby promoting N2O production by denitrification and N2O/(N2O + N2) product ratio in acidic soils. Consequently, soil N2O emission was increased with manure application in acidic soils. This study provides novel insight and improves our understanding of how soil pH regulates nitrification, denitrification, and N2O emissions from soils amended with chemical fertilizer and manure, which gives guidance on developing N management strategies for sustainable production and N2O mitigation in acid soils.

The content of organic matter in the soil, its labile (hot water extractable carbon–HWEC) and stable (soil organic carbon–SOC) form is a fundamental factor affecting soil productivity and health. The current research in soil organic matter (SOM) is focused on individual fragmented approaches and comprehensive evaluation of HWEC and SOC changes. The present state of the soil together with soil’s management practices are usually monitoring today but there has not been any common model for both that has been published. Our approach should help to assess the changes in HWEC and SOC content depending on the physico-chemical properties and soil´s management practices (e.g., digestate application, livestock and mineral fertilisers, post-harvest residues, etc.). The one- and multidimensional linear regressions were used. Data were obtained from the various soil´s climatic conditions (68 localities) of the Czech Republic. The Czech farms in operating conditions were observed during the period 2008–2018. The obtained results of ll monitored experimental sites showed increasing in the SOC content, while the HWEC content has decreased. Furthermore, a decline in pH and soil´s saturation was documented by regression modelling. Mainly digestate application was responsible for this negative consequence across all soils in studied climatic regions. The multivariate linear regression models (MLR) also showed that HWEC content is significantly affected by natural soil fertility (soil type), phosphorus content (−30%), digestate application (+29%), saturation of the soil sorption complex (SEBCT, 21%) and the dose of total nitrogen (N) applied into the soil (−20%). Here we report that the labile forms (HWEC) are affected by the application of digestate (15%), the soil saturation (37%), the application of mineral potassium (−7%), soil pH (−14%) and the overall condition of the soil (−27%). The stable components (SOM) are affected by the content of HWEC (17%), soil texture 0.01–0.001mm (10%), and input of organic matter and nutrients from animal production (10%). Results also showed that the mineral fertilization has a negative effect (−14%), together with the soil depth (−11%), and the soil texture 0.25–2 mm (−21%) on SOM. Using modern statistical procedures (MRLs) it was confirmed that SOM plays an important role in maintaining resp. improving soil physical, biochemical and biological properties, which is particularly important to ensure the productivity of agroecosystems (soil quality and health) and to future food security.

With economic development and improvements in living standards, the demand for livestock products has steadily increased, resulting in the generation of large amounts of livestock manure, which seriously pollutes the ecological environment and poses a threat to human health. High-temperature aerobic composting is an effective method for treating livestock manure; however, traditional composting processes often lead to considerable nitrogen loss, reduced efficiency of soil conditioners, and increased emissions of harmful gases. The incorporation of physical, chemical, and biological additives can effectively retain nitrogen within the compost. Among these, microbial agents are particularly noteworthy as they precisely regulate the microbial community structure associated with nitrogen transformation during aerobic composting, altering the abundance of functional genes and enzyme activities involved in nitrogen transformation. This approach significantly reduces nitrogen loss and harmful gas emissions. This paper reviews the application effects of microbial agents on nitrogen retention during aerobic composting and explores the underlying regulatory mechanisms, aiming to provide theoretical guidance and new research directions for the application of microbial agents in enhancing nitrogen retention during aerobic composting.

Adopting waste-to-wealth strategies and circular economy models can help reduce biowaste and add value. For instance, poultry farming is an essential source of protein, and chicken manure can be converted into renewable energy through anaerobic digestion. However, there are a number of restrictions that prevent the utilization of chicken manure in bioenergy production. Here, we review the conversion of chicken manure into biomethane by anaerobic digestion with focus on limiting factors, strategies to enhance digestion, and valorization. Limiting factors include antibiotics, ammonia, fatty acids, trace elements, and organic compounds. Digestion can be enhanced by co-digestion with sludge, lignocellulosic materials, food waste, and green waste; by addition of additives such as chars, hydrochars, and conductive nanoparticles; and by improving the bacterial community. Chicken manure can be valorized by composting, pyrolysis, and gasification. We found that the growth of anaerobic organisms is inhibited by low carbon-to-nitrogen ratios. The total biogas yield decreased from 450.4 to 211.0 mL/g volatile solids in the presence of Staphylococcus aureus and chlortetracycline in chicken manure. A chlortetracycline concentration of 60 mg/kg or less is optimal for biomethanization, whereas higher concentrations can inhibit biomethane production. The biomethane productivity is reduced by 56% at oxytetracycline concentrations of 10 mg/L in the manure. Tylosin concentration exceeding 167 mg/L in the manure highly deteriorated the biomethane productivity due to an accumulation of acetate and propionate in the fermentation medium. Anaerobic co-digestion of 10% of primary sludge to 90% of chicken manure increased the biogas yield up to 8570 mL/g volatile solids. Moreover, chemicals such as biochar, hydrochar, and conducting materials can boost anaerobic digestion by promoting direct interspecies electron transfer. For instance, the biomethane yield from the anaerobic digestion of chicken manure was improved by a value of 38% by supplementation of biochar.