Effects of Zeolite and Biochar Addition on Ammonia-Oxidizing Bacteria and Ammonia-Oxidizing Archaea Communities during Agricultural Waste Composting

Nitrogen-enriched biochar co-compost for the amelioration of degraded tropical soil

Tropical soils are often deeply weathered and vulnerable to degradation having low pH and unfavorable Al/Fe levels, which can constrain crop production. This study aims to examine nitrogen-enriched novel biochar co-composts prepared from rice straw, maize stover, and gram residue in various mixing ratios of the biochar and their feedstock materials for the amelioration of acidic tropical soil. Three pristine biochar and six co-composts were prepared, characterized, and evaluated for improving the chemical and biological quality of the soil against a conventional lime treatment. The pH, cation exchange capacity (CEC), calcium carbonate equivalence (CCE) and nitrogen content of co-composts varied between 7.78-8.86, 25.3-30.5 cmol (p+) kg-1, 25.5-30.5%, and 0.81-1.05%, respectively. The co-compost prepared from gram residue biochar mixed with maize stover at a 1:7 dry-weight ratio showed the highest rise in soil pH and CEC, giving an identical performance with the lime treatment and significantly better effect (p < .05) than the unamended control. Agglomerates of calcite and dolomite in biochar co-composts, and surface functional groups contributed to pH neutralization and increased CEC of the amended soil. The co-composts also significantly (p < .05) increased the dehydrogenase (1.87 µg TPF g-1 soil h-1), β-glucosidase (90 µg PNP g-1 soil h-1), and leucine amino peptidase (3.22 µmol MUC g-1 soil h-1) enzyme activities in the soil, thereby improving the soil's biological quality. The results of this study are encouraging for small-scale farmers in tropical developing countries to sustainably reutilize crop residues via biochar-based co-composting technology.

Effects of biochar and biogas residue amendments on N2O emission, enzyme activities and functional genes related with nitrification and denitrification during rice straw composting

This study was carried out to determine the response characteristics of N₂O emission, enzyme activities, and functional gene abundances involved in nitrification/denitirification process with biochar and biogas residue amendments during rice straw composting. The results revealed that N₂O release mainly occurred during the second fermentation phase. Biogas residue amendment promoted N₂O emission, while biochar addition decreased its emission by 33.6%. The nirK gene was abundant through composting process. Biogas residues increased the abundance of denitrification genes, resulting in further release of N₂O. Biochar enhanced nosZ gene abundance and accelerated the reduction of N₂O. Nitrate reductase (NR), nitrite reductase (NiR), N₂O reductase (N₂OR), and ammonia monooxygenase (AMO) activities were greatly stimulated by biochar or biogas residue rather than their combined addition. Pearson regression analysis indicated that N₂O emission negatively correlated with ammonium and positively correlated with nosZ, nirK, 18S rDNA, total nitrogen, and nitrate (P < 0.05).

Effectiveness of Biochar and Zeolite Soil Amendments in Reducing Pollution of Municipal Wastewater from Nitrogen and Coliforms

A greenhouse experiment with soil cores and wastewater application was carried out to investigate the effects of biochar and zeolite on the mobility of nitrogen and coliform bacteria during the leaching of columns repacked by a silty loam soil. Triticum aestivum plants were grown in cores with and without biochar and zeolite irrigated with municipal wastewater for 4 months in the greenhouse. Cores were then flushed with 800 mLof distillate water and, finally, the leachate was collected. Application of biochar or zeolite significantly (p ≤ 0.05) reduced nitrate and ammonium loss in soil after leaching process, compared to their non-treated counterparts. In addition, interactions of biochar and zeolite significantly decreased nitrate and ammonium content in leachate. Biochar had higher removal effects of coliform bacteria in leachate than zeolite. Lower nitrate and ammonium content in leachate was related to the increased retention of soil amendments. Application of 5% w/w of biochar also reduced the volume of leachate by 11% compare to control, but using 5% w/w and 10% w/w of zeolite increased the volume of leachate compared with non-treated columns by 21% and 48%, respectively. Taken together, these data highlight the need to consider the potential benefits of biochar and zeolite as soil amendment to reduce nitrogen mobility and remove coliform bacteria in the leaching process of municipal wastewater in agricultural systems.

Responses of ammonia-oxidizing microorganisms to biochar and compost amendments of heavy metals-polluted soil

Heavy metal pollution affects soil ecological function. Biochar and compost can effectively remediate heavy metals and increase soil nutrients. The effects and mechanisms of biochar and compost amendments on soil nitrogen cycle function in heavy-metal contaminated soils are not fully understood. This study examined how biochar, compost, and their integrated use affected ammonia-oxidizing microorganisms in heavy metal polluted soil. Quantitative PCR was used to determine the abundance of ammonia-oxidizing archaea (AOA) and bacteria (AOB). Ammonia monooxygenase (AMO) activity was evaluated by the enzyme-linked immunosorbent assay. Results showed that compost rather than biochar improved nitrogen conversion in soil. Biochar, compost, or their integrated application significantly reduced the effective Zn and Cd speciation. Adding compost obviously increased As and Cu effective speciation, bacterial 16S rRNA abundance, and AMO activity. AOB, stimulated by compost addition, was significantly more abundant than AOA throughout remediation. Correlation analysis showed that AOB abundance positively correlated with NO₃^--N (r = 0.830, P < 0.01), and that AMO activity had significant correlation with EC (r = -0.908, P < 0.01) and water-soluble carbon (r = -0.868, P < 0.01). Those seem to be the most vital factors affecting AOB community and their function in heavy metal-polluted soil remediated by biochar and compost.

Bacterial and Fungal Community Dynamics and Shaping Factors During Agricultural Waste Composting with Zeolite and Biochar Addition

Bacterial and fungal communities play significant roles in waste biodegradation and nutrient reservation during composting. Biochar and zeolite were widely reported to directly or indirectly promote microbial growth. Therefore, the effects of zeolite and biochar on the abundance and structure of bacterial and fungal communities and their shaping factors during the composting of agricultural waste were studied. Four treatments were carried out as follows: Run A as the control without any addition, Run B with zeolite (5%), Run C with biochar (5%), and Run D with zeolite (5%) and biochar (5%), respectively. The bacterial and fungal community structures were detected by high-throughput sequencing. Redundancy analysis was used for determining the relationship between community structure and physico-chemical parameters. The results indicated that the addition of biochar and zeolite changed the physico-chemical parameters (e.g., pile temperature, pH, total organic matter, ammonium, nitrate, and water-soluble carbon) during the composting process. Zeolite and biochar significantly changed the structure and diversity of bacterial and fungal populations. Moreover, the bacterial community rather than the fungal community was sensitive to the biochar and zeolite addition during the composting process. Community phylogenetic characteristics showed that Nocardiopsaceae, Bacillaceae, Leuconostocaceae, Phyllobacteriaceae, and Xanthomonadaceae were the predominant bacterial species at the family-level. Chaetomiaceae and Trichocomaceae were the two most dominant fungal species. The pH, total organic matter, and nitrate were the most important factors affecting the bacterial and fungal population changes during the composting process.