The over-use of antibiotics in animal husbandry in China and the concomitant enhanced selection of antibiotic resistance genes (ARGs) in animal manures are of serious concern. Thermophilic composting is an effective way of reducing hazards in organic wastes. However, its effectiveness in antibiotic degradation and ARG reduction in commercial operations remains unclear. In the present study, we determined the concentrations of 15 common veterinary antibiotics and the abundances of 213 ARGs and 10 marker genes for mobile genetic elements (MGEs) in commercial composts made from cattle, poultry and swine manures in Eastern China. High concentrations of fluoroquinolones were found in the poultry and swine composts, suggesting insufficient removal of these antibiotics by commercial thermophilic composting. Total ARGs in the cattle and poultry manures were as high as 1.9 and 5.5 copies per bacterial cell, respectively. After thermophilic composting, the ARG abundance in the mature compost decreased to 9.6% and 31.7% of that in the cattle and poultry manure, respectively. However, some ARGs (e.g. aadA, aadA2, qacEΔ1, tetL) and MGE marker genes (e.g. cintI-1, intI-1 and tnpA-04) were persistent with high abundance in the composts. The antibiotics that were detected at high levels in the composts (e.g. norfloxacin and ofloxacin) might have posed a selection pressure on ARGs. MGE marker genes were found to correlate closely with ARGs at the levels of individual gene, resistance class and total abundance, suggesting that MGEs and ARGs are closely associated in their persistence in the composts under antibiotic selection. Our research shows potential disseminations of antibiotics and ARGs via compost utilization.

The presence of antibiotics in animal manure represents a significant concern with respect to the introduction of antibiotic residues to the environment and the development of antibiotic-resistant pathogens. In this review, we have (1) compiled reported detections of antibiotics in poultry litter, swine manure, and cattle manure; and (2) discussed the treatment of antibiotics during conventional agricultural waste management practices. The most reported antibiotics in animal manure were fluoroquinolones, sulfonamides, and tetracyclines, all of which the World Health Organization has listed as critically important for human health. Relatively high treatment efficiencies were observed for antibiotics in composting, anaerobic digestion, and aerobic/anaerobic lagooning. Interestingly, active management of compost piles did not demonstrate a significant increase in antibiotic degradation; however, low- and high-intensity compost systems exhibited high treatment efficiencies for most antibiotics. Anaerobic digestion was not effective for some key antibiotics, including lincosamides and select sulfonamides and fluoroquinolones. Given the potential for energy recovery during anaerobic digestion of agricultural waste, efforts to optimize antibiotic degradation represent an important area for future research. Lagoons also exhibited fairly high levels of antibiotic treatment, especially for aerobic systems; however, the operational costs/complexity of these systems inhibit utilization at the full-scale. No overall trends in antibiotic treatment efficiency during these three agricultural waste management practices were observed. Finally, we posit that increased efforts to include analysis of antibiotic residues in animal manure in national surveillance programs will provide important information to address concerns over the continued use of antimicrobials in animal feeding operations.

Studies on replacement of inorganic fertilizer with organic residues to improve crop productivity and their impact on greenhouse gas emission from agricultural soil merit more attention. Two-year field experiments were conducted to study the impact of different organic residues with varied carbon (C)/nitrogen (N) ratios as substitutes of chemical fertilizer on emission reduction of nitrous oxide (N₂O) and crop yield from a tropical summer rice paddy of India. Five treatments comprising of conventional N fertilizer (NPK), cow manure (CD), rice straw (RS), poultry manure (PM), and sugarcane bagasse (SCB) were applied in a rice field to estimate N₂O emission. Application of CD (at 10 t ha⁻¹) resulted in maximum reduction of seasonal N₂O emissions (15 %) over NPK, RS, PM, and SCB. Application of CD and RS enhanced leaf photosynthetic rate and caused maximum utilization of photosynthates towards developing grains as evident from grain filling ability and higher grain yield. Substitution of NPK with organic residues enhanced soil nutrient availability in terms of C and N resulting in improved soil fertility and to some extent influenced soil nitrogen processes which in turn reduced N₂O emissions. We conclude that suitable management of soil in agricultural ecosystem can reduce the emission of N₂O and protect and preserve the soil health without compromising the agronomic productivity reducing the use of chemical fertilizer and maintaining the sustainability of rice ecosystem as evident from lower carbon equivalent emissions (CEE) and higher carbon efficiency ratio (CER) at CD in rice paddies in the present study.

The main objective of the present study was to determine the optimum C/N ratio for converting waste paper and chicken manure to nutrient-rich manure with minimum toxicity. Six treatments of C/N ratio 20, 30, 40, 50, 60, and 70 (T1, T2, T3, T4, T5, and T6, respectively) achieved by mixing chicken manure with shredded paper were used. The study involved a composting stage for 20 days followed by vermicomposting with Eisenia fetida for 7 weeks. The results revealed that 20 days of composting considerably degraded the organic waste mixtures from all treatments and a further 7 weeks of vermiculture significantly improved the bioconversion and nutrient value of all treatments. The C/N ratio of 40 (T3) resulted in the best quality vermicompost compared to the other treatments. Earthworm biomass was highest at T3 and T4 possibly due to a greater reduction of toxic substances in these waste mixtures. The total N, total P, and total K concentrations increased with time while total carbon, C/N ratio, electrical conductivity (EC), and heavy metal content gradually decreased with time during the vermicomposting process. Scanning electron microscopy (SEM) revealed the intrastructural degradation of the chicken manure and shredded paper matrix which confirmed the extent of biodegradation of treatment mixtures as result of the composting and vermicomposting processes. Phytotoxicity evaluation of final vermicomposts using tomato (Lycopersicon esculentum), radish (Raphanus sativus), carrot (Daucus carota), and onion (Allium cepa) as test crops showed the non-phytotoxicity of the vermicomposts to be in the order T3 > T4 > T2 > T1 > T5 > T6. Generally, the results indicated that the combination of composting and vermicomposting processes is a good strategy for the management of chicken manure/paper waste mixtures and that the ideal C/N ratio of the waste mixture is 40 (T3).

The use of poultry waste (without proper treatment) as a potential fertilizer in agricultural soils have great concern to environment and human health, due to high levels of organic and inorganic toxicants, including heavy metals. Thus, the aim of this study was to monitor and assess bio-accumulation of heavy metals, cadmium (Cd), copper (Cu), Iron (Fe), lead (Pb), and zinc (Zn) contained in soil amended with poultry waste (SPW) and compared with controls. The physico-chemical parameters and heavy metal concentration in control soil (CS), poultry waste (PW), and SPW samples was also determined. The comparison study between the test vegetables and controls showed that the concentrations of Cd, Cu, Fe, Pb, and Zn in edible parts of chili pepper were found to be 0.057, 38.0, 61.9, 1.02, and 51.1 mg kg⁻¹, respectively, while the levels of Cd, Cu, Fe, Pb, and Zn were 0.14, 28.7, 138, 3.67, and 64.7 mg kg⁻¹, respectively, in coriander grown on SPW. The uptakes of heavy metals in test vegetables were found to be 35.7 to 95.6 % higher as compared with control vegetables. Soil-to-vegetable transfer factor values for all heavy metals in test samples were higher than control samples (p < 0.05). The enrichment factor values were >1.05, which indicated that the source of heavy metal contamination in the studied area was anthropogenic. Graphical Abstract Fate of heavy metals from poultry manure to agricultural soil

Using hyperaccumulator plants is an important method to remove heavy metals from contaminated land. Carpobrotus rossii, a newly found Cd hyperaccumulator, has shown potential to remediate Cd-contaminated soils. This study examined the effect of nitrogen forms on Cd phytoextraction by C. rossii. The plants were grown for 78 days in an acid soil spiked with 20 mg Cd kg⁻¹ and supplied with (NH₄)₂SO₄, Ca(NO₃)₂, urea, and chicken manure as nitrogen (N) fertilizers. Nitrification inhibitor dicyandiamide (DCD) was applied to maintain the ammonium (NH₄ ⁺) form. Nitrogen fertilization increased shoot biomass but decreased root biomass with the highest shoot biomass occurring in the manure treatment. Compared to the no-N control, urea application did not affect shoot Cd concentration, but increased Cd content by 17 % due to shoot biomass increase. Chicken manure significantly decreased CaCl₂-extractable Cd in soil, and the Cd concentration and total Cd uptake in the plant. Rhizosphere pH was the highest in the manure treatment and the lowest in the NH₄ ⁺ treatments. The manure and nitrate (NO₃ ⁻) treatments tended to have higher rhizosphere pH than their respective bulk soil pH, whereas the opposite was observed for urea and NH₄ ⁺ treatments. Furthermore, the concentrations of extractable Cd in soil and Cd in the plant correlated negatively with rhizosphere pH. The study concludes that urea significantly enhanced the Cd phytoaccumulation by C. rossii while chicken manure decreased Cd availability in soil and thus the phytoextraction efficiency.

Co-composting biowastes such as manures and biosolids can be used to stabilize carbon (C) without impacting the quality of these biowastes. This study investigated the effect of co-composting biowastes with alkaline materials on C stabilization and monitored the fertilization and revegetation values of these co-composts. The stabilization of C in biowastes (poultry manure and biosolids) was examined by their composting in the presence of various alkaline amendments (lime, fluidized bed boiler ash, flue gas desulphurization gypsum, and red mud) for 6 months in a controlled environment. The effects of co-composting on the biowastes’ properties were assessed for different physical C fractions, microbial biomass C, priming effect, potentially mineralizable nitrogen, bioavailable phosphorus, and revegetation of an urban landfill soil. Co-composting biowastes with alkaline materials increased C stabilization, attributed to interaction with alkaline materials, thereby protecting it from microbial decomposition. The co-composted biowastes also increased the fertility of the landfill soil, thereby enhancing its revegetation potential. Stabilization of biowastes using alkaline materials through co-composting maintains their fertilization value in terms of improving plant growth. The co-composted biowastes also contribute to long-term soil C sequestration and reduction of bioavailability of heavy metals.

This study aims to examine the effects of different organic treatments including compost (generated from cattle hide waste and plant material), compost mixed with biochar (compost + biochar) and a new formulation of organo-mineral biochar (produced by mixing biochar with clay, minerals and chicken manure) on carbon (C) nitrogen (N) cycling. We used compost at the rate of 20 t ha⁻¹, compost 20 t ha⁻¹ mixed with 10 t ha⁻¹ biochar (compost + biochar) and organo-mineral biochar which also contained 10 t ha⁻¹ biochar. Control samples received neither of the treatments. Compost and compost + biochar increased NH₄⁺ -N concentrations for a short time, mainly due to the release of their NH₄⁺ -N content. Compost + biochar did not alter N cycling of the compost significantly but did significantly increase CO₂ emission compared to control. Compost significantly increased N₂O emission compared to control. Compost + biochar did not significantly change N supply and also did not decrease CO₂ and N₂O emissions compared to compost, suggesting probably higher rates of biochar may be required to be added to the compost to significantly affect compost-induced C and N alteration. The organo-mineral biochar had no effect on N cycling and did not stimulate CO₂ and N₂O emission compared to the control. However, organo-mineral biochar maintained significantly higher dissolved organic carbon (DOC) than compost and compost + biochar from after day 14 to the end of the incubation. Biochar used in organo-mineral biochar had increased organic C adsorption which may become available eventually. However, increased DOC in organo-mineral biochar probably originated from both biochar and chicken manure which was not differentiated in this experiment. Hence, in our experiment, compost, compost + biochar and organo-mineral biochar affected C and N cycling differently mainly due to their different content.

The rate of degradation of enrofloxacin in broiler chicken manure has been characterized in the laboratory according to the CVMP guideline on determining the fate of veterinary medicinal products in manure. Degradation was followed in a flow-through system under aerobic and anaerobic conditions, in the dark and in the presence of light. The rate of degradation of enrofloxacin and the formation of its degradation products are dependent on laboratory conditions. A rapid degradation of enrofloxacin in the dark was noticed, where a shorter degradation half-life under aerobic (DT₅₀ = 59.1 days), comparing to anaerobic conditions (DT₅₀ = 88.9 days), was determined. The presence of light slowed down the enrofloxacin degradation half-life, which was significantly shorter under aerobic (DT₅₀ = 115.0 days), comparing to anaerobic conditions (DT₅₀ = 190.8 days). Desethylene-enrofoxacin was the only degradation product formed, its concentrations ranged from 2.5 to 14.9 %. The concentration of the degradation product was approximately 2.5-fold higher under aerobic conditions. Enrofloxacin degradation in sterile manure incubated under sterile conditions was marginal comparing to non-sterile conditions; after 120 days of incubation, approximately 80 % of enrofloxacin was still present in manure and only 1 % of desethylene-enrofloxacin was formed. The present work demonstrates that enrofloxacin degradation in chicken manure is relatively fast when incubated in the dark under aerobic conditions which is the recommended incubation system for chicken manure according to CVMP guideline.

Water spinach (Ipomoea aquatic Forsk.) was selected to investigate the effects of oxytetracycline (OTC) on the toxicity of soil contaminated by long-term sewage irrigation. After acute toxicity test in petri dish at nine different OTC-spiked levels for 48 h, the germination rate was found to be generally inhibited in all treatments treated with OTC but the root elongation and activities of several antioxidant enzymes, superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) were either forward or backward stimulated to varying extent. During a 60-day sub-chronic toxicity test by means of a pot experiment, activities of SOD, POD and CAT in both the leaf and root tissue at 25 mg OTC per kg soil (dry weight) and in root tissue at 1 mg OTC per kg soil (dry weight) were significantly different than those in other treatments, which also indicated the higher sensitivity of the root. The foliar photosynthetic rate, stomatal conductance and transpiration rate were all gradually inhibited in spite of elevated water use efficiency under the pressure of the different OTC concentrations, which were highly significant different at 10 mg OTC per kg soil (dry weight). Indices of soil microbial diversity at 4 mg OTC kg⁻¹ soil were significantly different from those of the control, indicating the potential adverse effects of OTC to soil microorganisms. The results suggest that the introduction of OTC could damage both plants and soil microorganisms, and during sub-chronic incubation, the sensitivity of different indices generally followed the order of root tissue antioxidant enzyme activities, soil microbial diversity indices, leaf photosynthesis-related index and leaf tissue enzyme antioxidant activities. In addition, the application of livestock and poultry manure containing pollutants like OTC in farmland soil, especially if the soil has been contaminated before, should be taken more seriously in the context of the current pursuit of increased agricultural production.