Rational application of treated sewage sludge with urea increases GHG mitigation opportunities in Mediterranean soils

• Published in: Agriculture, ecosystems & environment Vol. 238; pp. 114 - 127
• Main Authors: Calleja-Cervantes, M.E., Aparicio-Tejo, P.M., Villadas, P.J., Irigoyen, I., Irañeta, J., Fernández-González, A.J., Fernández-López, M., Menéndez, S.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.02.2017; Elsevier BV
• Subjects: 16s; Agrochemicals; Air pollution; Ammonium; Annual variations; Bacteria; Bacterial diversity; Biological activity; Carbon dioxide; Carbon sequestration; Communities; Community structure; Crops; Data processing; Denitrification; Deoxyribonucleic acid; DNA; Emissions; Emissions control; Enzymes; Erosion; Evaluation; Fertilization; Fertilizers; Gene sequencing; GHG emissions; Greenhouse effect; Greenhouse gases; Hydroxyapatite; Lodging; Mediterranean soils; Metabolism; Microbial activity; Mineral fertilizers; Mitigation; Nitrates; Nitrification; Nitrogen; Nucleotide sequence; Nutrients; Organic matter; Seasonal variations; Sewage sludge; Sewage treatment; Sludge; Sludge digestion; Soil amendment; Soil enzymes; Soil erosion; Soil microorganisms; Soil structure; Soils; Studies; Treated sewage; Urea; Mediterranean Area; PCoA; C; OTUs; CO2; GHG; H; GHG emissions; K; M; N; P; FW; Soil enzymes; DW; Na; NO3; CaCO3; yr; mg; GC; kg; OM; w/w; RDP; CCA; FID; MgCl2; d; Bacterial diversity; Fertilization; rRNA; ECD; N2O; CH4; 16s; UPGMA; TSS; DNA; NH3; ha; NH4; Mediterranean soils; Ca; PCR
• ISSN: 0167-8809; 1873-2305
• DOI: 10.1016/j.agee.2016.09.021

•After 20-years of TSS application to Mediterranean soils, soil enzyme activities and C and N contents are increased.•The studied doses of TSS induce GHG fluxes, change soil microbial structure and cause crop lodging.•The application of TSS with urea induces carbon sequestration and increases fertility, whilst maintaining GHG emissions.•TSS application to soil is a viable option for waste recycling as long as doses remain rational. Mediterranean soils, which are carbonate-rich and organic matter-poor, are prone to erosion and important carbon losses due to seasonal changes associated with dry summers and wet winters. The use of thermophilic digested sewage sludge (TSS) in these agricultural systems, as a soil amendment, has been acknowledged as an interesting way to supply organic matter and nutrients. Data on the long-term evaluation of TSS applied to Mediterranean soils are scarce. Moreover, the effect of the application is unpredictable because of the intrinsic variation in the TSS. The scope of this study was to determine whether the continued application of TSS for 20 years leads to increased carbon sequestration in the soil without affecting emissions of greenhouse gases. To conduct this evaluation, the doses applied since 1992 have been as follows: 40tha−1 and 80tha−1 every year, and 40tha−1 every 3 years, plus annual mineral N fertilization depending on the crop. A control without TSS or mineral fertilization and a treatment with only mineral N fertilizer were also evaluated. In this case, urea was used as the mineral treatment. The TSS doses were applied annually in October, while the mineral was split into one dose around January and another in March. The chemical parameters, greenhouse gas emissions, nitrate and ammonium concentrations of the soil were measured during the crop cycle. The bacterial community and enzymes in the soil were surveyed 15days after the last annual application and at harvest. Fifteen days after fertilization with TSS and urea, nitrification and denitrification potentials were measured. The 80tha−1yr−1 dose yielded the most significant increase in total carbon, organic matter content, P2O5, and total nitrogen. This same treatment significantly increased GHG emissions for all gases concerned. Similar results were found in the 40tha−13yr−1 and urea for CO2 and CO2eq ha−1. TSS application increased soil enzyme activities. According to the microbial diversity results, 80% of the DNA sequences corresponded to 6 main phyla: (from most to least) Proteobacteria, Acidobacteria, Actinobacteria, Bacteroidetes, Chloroflexi and Verrucomicrobia with unclassified material making up an average 10.94% of the sequences. The soil microbial community structure only altered with the 80tha−1yr−1 dose. The highest dose of TSS applied in this study resulted in the irreversible lodging of the crop and a concomitant decrease in yield. In the 40tha−13yr−1 treatment, interesting similarities were found with urea alone. In summary, rational application of TSS, such as 40tha−13yr−1 dose, along with urea, trigger a beneficial increase in microbial activity in soil, that ultimately activates soil metabolism and enhances carbon sequestration possibilities, while GHG emissions remain at the same level as with urea alone. The results support the hypothesis that TSS can induce carbon sequestration without increasing GHG emissions. TSS has proven to exert beneficial outcomes under Mediterranean conditions; additionally, its application offers a viable opportunity for converting this by-product into a fertilizer. However, application rates must be adjusted or it should be used together with mineral fertilization.