Biogas digestates affect crop P uptake and soil microbial community composition

Solid-liquid separation of digestate from biogas plants: A systematic review of the techniques' performance

Digestate processing is a strategy to improve the management of digestate from biogas plants. Solid-liquid separation is usually the primary step and can be followed by advanced treatments of the fractions. The knowledge about the performance of the separators and the quality of the fractions is scattered because of many available techniques and large variability in digestate characteristics. We performed a systematic review and found 175 observations of full-scale solid-liquid separation of digestate. We identified 4 separator groups, 4 digestate classes based on substrate, and distinguished whether chemical conditioners were used. We confirmed the hypothesis that the dominant substrate can affect the efficiency of the digestate separation. Furthermore, the results showed that centrifuges separated significantly more dry matter and total P than screw presses. Use of chemical conditioners in combination with a centrifuge lowered the dry matter concentration in the liquid fraction by 30%. Screw presses consumed 4.5 times less energy than centrifuges and delivered 3.3 tonne ammonium N in the liquid fraction and 0.3 tonne total P in the solid fraction using 1 MWh. The results can provide data for systems analyses of biogas solutions and can support practitioners when choosing among full-scale separator techniques depending on the digestate type. In a broader perspective, this work contributes to the continuous improvement of biogas plants operations and to their role as nutrients recovery sites.

Surge of native rare taxa in tailings soil induced by peat bacterial invasion

The pivotal role of the native bacterial community in maintaining soil health, particularly in degraded tailings environments, is often overlooked. This study utilized peat, rich in microorganisms, to investigate its impact on soil function and native bacteria response in copper tailings-soil. Through 16S rRNA gene sequencing, changes in nutrient cycling, organic matter decomposition, and microbial activity were assessed post one-year peat remediation. Results from FEAST and cluster analysis revealed that peat-derived species disproportionately influenced tailings microbial community remediation, supported by the microbial invasion theory. Tailings responded positively to these species, with optimal function achieved at 5 % peat dosage. Peat biomarkers (Actinobacteriota, Bacteroida, Chloroflexi, and Firmicutes) played key roles in heavy metal removal and nutrition fixation. The Random Forest model and co-occurrence network highlighted contributions from native rare species (Dependentiae and Latescibacterota) activated by peat addition. These insights underscore the resilience of rare taxa and provide a foundation for soil health restoration in tailings areas. By emphasizing the importance of peat as a potential exogenous solution for activating indigenous microbial functions, these findings offer valuable insights for developing effective and sustainable remediation strategies in mining-affected regions.

Does the application of biogas slurry reduce soil N2O emissions and increase crop yield?-A systematic review

The use of organic fertilizer for agricultural production can reduce the use of chemical fertilizer (CF), reduce greenhouse gas emissions, and maintain crop production. However, biogas slurry (BS), a liquid with a high moisture content and a low C/N ratio, differs from commercial organic fertilizer and manure in terms of its impact on the soil N cycle. Replacing CF with BS needs to be reconsidered regarding soil nitrous oxide (N₂O) emissions and crop production in terms of fertilization, agricultural land type, and soil characteristics. For this systematic review, the results of 92 published studies worldwide were collected. Based on the findings, the combined application of BS and CF can significantly increase soil total N (TN), microbial biomass N (MBN), and soil organic matter (SOM) levels. The Chaol and ACE index values of soil bacteria were increased by 13.58% and 18.53%, whereas those of soil fungi were decreased by 10.45% and 14.53%, respectively. At a replacement ratio (rr) ≤ 70%, crop yield was promoted by 2.20%-12.17%, and soil N₂O emissions were reduced by 1.94%-21.81%. A small rr (≤30%) was more conducive to growth, and a moderate rr (30% < rr ≤ 70%) was more favorable for N₂O emission reduction, especially in the dryland crop system. However, at rr = 100%, soil N₂O emissions in neutral and alkaline dryland soil were increased by 28.56%-32.22%. The importance analysis of the influencing factors showed that the proportion of BS, the N application rate, and the temperature were the factors affecting soil N₂O emissions. Our results provide a scientific basis for the safe use of BS in agricultural systems.

Impacts of Biogas Slurry Fertilization on Arbuscular Mycorrhizal Fungal Communities in the Rhizospheric Soil of Poplar Plantations

The majority of terrestrial plants are symbiotic with arbuscular mycorrhizal fungi (AMF). Plants supply carbohydrates to microbes, whereas AMF provide plants with water and other necessary nutrients-most typically, phosphorus. Understanding the response of the AMF community structure to biogas slurry (BS) fertilization is of great significance for sustainable forest management. This study aimed to look into the effects of BS fertilization at different concentrations on AMF community structures in rhizospheric soil in poplar plantations. We found that different fertilization concentrations dramatically affected the diversity of AMF in the rhizospheric soil of the poplar plantations, and the treatment with a high BS concentration showed the highest Shannon diversity of AMF and OTU richness (Chao1). Further analyses revealed that Glomerales, as the predominant order, accounted for 36.2-42.7% of the AMF communities, and the relative abundance of Glomerales exhibited negligible changes with different BS fertilization concentrations, whereas the order Paraglomerales increased significantly in both the low- and high-concentration treatments in comparison with the control. Furthermore, the addition of BS drastically enhanced the relative abundance of the dominant genera, Glomus and Paraglomus. The application of BS could also distinguish the AMF community composition in the rhizospheric soil well. An RDA analysis indicated that the dominant genus Glomus was significantly positively correlated with nitrate reductase activity, while Paraglomus showed a significant positive correlation with available P. Overall, the findings suggest that adding BS fertilizer to poplar plantations can elevate the diversity of AMF communities in rhizospheric soil and the relative abundance of some critical genera that affect plant nutrient uptake.

Research Progress in the Field of Microbial Mitigation of Drought Stress in Plants

Plants defend themselves against ecological stresses including drought. Therefore, they adopt various strategies to cope with stress, such as seepage and drought tolerance mechanisms, which allow plant development under drought conditions. There is evidence that microbes play a role in plant drought tolerance. In this study, we presented a review of the literature describing the initiation of drought tolerance mediated by plant inoculation with fungi, bacteria, viruses, and several bacterial elements, as well as the plant transduction pathways identified via archetypal functional or morphological annotations and contemporary "omics" technologies. Overall, microbial associations play a potential role in mediating plant protection responses to drought, which is an important factor for agricultural manufacturing systems that are affected by fluctuating climate.

The Effects of Soil Application of Digestate Enriched with P, K, Mg and B on Yield and Processing Value of Sugar Beets

The aim of this research was to find out if the supplementation of digestate, a by-product of the anaerobic digestion of sugar beet pulp, with phosphorus, potassium, magnesium and boron can improve digestate performance as a soil amendment. The materials of this study were: digestate and sugar beet roots (Beta vulgaris cv. Fighter). A field trial was carried out on sugar beet growth under soil application conditions of solid and liquid digestate fractions with or without supplementation with P, K, Mg and B. It was shown that the root yield obtained from the plots amended with digestate supplemented with P, K, Mg and B was higher compared to the yield of other treatments. Soil amendment with digestate supplemented with P, K, Mg and B affected quality parameters of sugar beet roots. An increase in the following parameters under the effects of enriched digestate application was found: sucrose content, dry residue, pomace content, inverted sugars, α-amino and amide nitrogen fractions, as well as sodium and potassium content. A reduction in the content of conductometric ash was noted but this difference was not proven. The enrichment of digestate with P, K, Mg and B resulted in the beneficial modification of beet roots’ processing parameters with the exception of the predicted content of sugar in molasses. In the case of the liquid fraction and its supplementation with P, K, Mg and B, six among eleven technological quality parameters were increased.

Application of Sugar Beet Pulp Digestate as a Soil Amendment in the Production of Energy Maize

This study aimed to determine the suitability of sugar beet pulp digestion by-products as soil amendments for maize grown for energy purposes. In a plot experiment, nitrogen fertilizer at a standard rate of 200 kg N ha−1 was applied as a control vs. treatment with solid and liquid digestate fractions. Digestate was obtained from a gasifier processing only sugar beet pulp. Following harvest, heating and calorific values were determined together with the yield and chemical composition of the maize cob and stover. It was found that soil amendment with crude (unseparated) digestate or its two fractions (separated into liquid and solid) produced higher yields of maize cobs and stover compared with the application of standard fertilizer. An analysis of the energy value of the maize plant revealed differences between the studied soil treatments. Cobs obtained from plots treated with the digestate showed higher calorific and heating values than those obtained from control plots; however, maize stover from control plots showed higher calorific and heating values compared with plants from other experimental plots. It can be concluded that by-products obtained from sugar beet pulp digestion can be alternatively used as a soil amendment for maize production in a crop rotation with sugar beet. Among studied amendments the solid fraction of the digestate was found to have the best performance.

Changes in soil organic carbon status and microbial community structure following biogas slurry application in a wheat-rice rotation

Biogas slurry is widely used as a crop fertilizer due to its available nitrogen content. However, it remains unclear how biogas slurry application affects soil organic carbon (SOC) status and soil microbial community under typical agricultural systems. Here, under a wheat-rice field experiment, we examined the responses of SOC and soil bacterial and fungal communities to biogas slurry application, both with (BSS) and without (BS) straw return, relative to chemical nitrogen fertilizer with (CFS) and without (CF) straw return. The BS treatment significantly increased total organic carbon (TOC) at all soil depths (0-60 cm), compared to CF. Greater TOC occurred at 20-40 cm depth under BSS relative to all other treatments. However, straw return had no impact on soil TOC content under the CF and CFS treatments. Labile organic carbon (LOC) in the topsoil and recalcitrant organic carbon (ROC) at 20-60 cm depth was significantly greater under BS relative to CF. The bacterial class Gammaproteobacteria and family Hyphomicrobiaceae were found to be specifically abundant under biogas slurry application after one year of wheat-rice double cropping. Network analyses showed that the soil bacterial community under biogas slurry application was more complex than under chemical fertilizer application, while the opposite was true for the fungal community. Correlations between network modules and the SOC fractions indicated that biogas slurry application stimulated soil bacteria and fungi to participate in SOC cycling. The module functionality supports our speculation that soil microorganisms degraded the biogas slurry derived-ROC in the topsoil. Overall, we conclude that substitution of chemical fertilizer with biogas slurry can be beneficial for increasing SOC stocks and, in systems with straw return, enhancing straw decomposition.

Fungal community composition change and heavy metal accumulation in response to the long-term application of anaerobically digested slurry in a paddy soil

Anaerobically digested slurry (ADS) has been widely used as a liquid fertilizer in agroecosystems. However, there is scant information on the effects of successive ADS applications on heavy metals (HMs) accumulation and fungal community composition in paddy soils. In this study, we conducted a field experiment over 10 years to assess the changes in soil HMs and fungal community composition under the long-term application of ADS in a paddy field. The four treatments were (1) no fertilizer (CK); (2) mineral fertilizer and 270 kg N ha^-1 from urea (MF); (3) 270 kg N ha^-1 from ADS (ADS1); and (4) 540 kg N ha^-1 from ADS (ADS2). The results revealed that ADS application improved paddy soil fertility compared to that under the MF treatment by increasing soil organic C (SOC), total N (TN) and available potassium (AK). Long-term application of ADS significantly increased soil total and available Zn (TZn and AZn) concentrations as compared to those under the MF treatment. However, there were no significant differences in the total and available Cu concentrations or the total Pb concentration between the ADS and MF treatments. Sequence analysis showed that application of ADS increased the fungal richness indexes (Chao1 and ACE) compared to MF treatment. Principal coordinate analysis (PCoA) showed that the soil fungal community compositions were significantly separated by high levels of ADS application. Long-term application of ADS increased the relative abundance of classes Sordariomycetes, Dothideomycetes and Agaricomycetes by 20.8-29.0%, 107.3-141.4% and 289.5-387.5%, respectively, but decreased that of Pezizomycetes by 14.0-33.0% compared to that under the MF treatment. At the genus level, compared to those under the MF treatment, the relative abundances of Pyrenochaetopsis and Myrothecium were significantly increased by the application of ADS, but those of Mrakia and Tetracladium were significantly decreased. Redundancy analysis (RDA) revealed that SOC, AZn and AP were the three most important factors affecting the fungal community composition of the paddy soil. Our findings suggested that fungal community composition could be affected by changes in the chemical properties and heavy metal contents of paddy soil under high application of ADS in the long term.

Biochar of distillers' grains anaerobic digestion residue: Influence of pyrolysis conditions on its characteristics and ammonium adsorptive optimization

To promote the sustainable development of the liquor/ethanol industry and environment protection, alternative ways to dispose of anaerobic digestion residue (ADR) are urgently required. This research aims at studying the effects of different residence times (RTs) (30, 60 and 120 min) and heating rates (HR) (2.5, 5.0 and 10.0°C min^-1) under 700°C on characteristics of ADR biochar as well as the optimization of ammonium (NH₄⁺) adsorption. Results showed that, with the increasing RT and HR, the aromaticity as well as the content of fixed carbon and elemental carbon of ADR biochar increased, but the pyrolysis yield, volatile matter content, elemental hydrogen, oxygen and polarity decreased. Biochar prepared at 60 min and 5.0°C min^-1 under 700°C presented the best development of orderly and honeycomb shape structures, highest specific surface area and maximal amount of NH₄⁺ adsorption (3.15 mg N g^-1). The multilayer heterogeneous adsorption process dominated the NH₄⁺ adsorption behaviour. And the maximal amount of NH₄⁺ adsorption was achieved with 4 g biochar L^-1 at pH 11.0 along with the order of the competitive effect of K⁺ > Na⁺ > Ca²⁺ > Mg²⁺. Furthermore, NH₄⁺ adsorption was exothermic. Thus, the present study demonstrated that ADR biochar has potential to adsorb NH₄⁺ from NH₄⁺ polluted water to meet environmental standards.

Cyclic and safety utilisation of Cu polluted biogas residue in saline-alkali soil

The proper disposal of copper (Cu) polluted plant residues after phytoremediation has attracted extensive attention. In this study, the Cu-polluted biogas residue produced through anaerobic digestion was applied directly. Wheat, soybean and pakchoi were grown in pots for four seasons over two years. The application dosage of Cu-polluted biogas residue was evaluated by measuring growth conditions of crops, Cu content in edible parts, and amelioration of saline-alkali soil. The results showed that the biomass of the crops, the content of soil organic matter, total N and available P and microbial diversity can be improved, and the Cu concentration of the edible parts was all lower than limit standard. Amendment with 2% biogas residue enhanced the growth of beneficial bacteria and fungi, and decreased the relative abundances of potentially pathogenic fungi in the saline-alkali soil. The results of this study provide a basis for the safe utilisation of copper-polluted plant residues.

Handling the phosphorus paradox in agriculture and natural ecosystems: Scarcity, necessity, and burden of P

This special issue of Ambio compiles a series of contributions made at the 8th International Phosphorus Workshop (IPW8), held in September 2016 in Rostock, Germany. The introducing overview article summarizes major published scientific findings in the time period from IPW7 (2015) until recently, including presentations from IPW8. The P issue was subdivided into four themes along the logical sequence of P utilization in production, environmental, and societal systems: (1) Sufficiency and efficiency of P utilization, especially in animal husbandry and crop production; (2) P recycling: technologies and product applications; (3) P fluxes and cycling in the environment; and (4) P governance. The latter two themes had separate sessions for the first time in the International Phosphorus Workshops series; thus, this overview presents a scene-setting rather than an overview of the latest research for these themes. In summary, this paper details new findings in agricultural and environmental P research, which indicate reduced P inputs, improved management options, and provide translations into governance options for a more sustainable P use.