October, 2018
Dr. Maria Silveira, UF/IFAS Range Cattle Research & Education Center, Ona

Biosolid application

Biosolids have clear agronomic benefits, but concerns over nutrient accumulation in soils and subsequent impacts on water quality can limit land application in Florida. The project described in this article addresses FCA Priorities # 9 “Land Application of Biosolids on Pastures” and # 1 “Fertilization (Alternative Fertilizer Sources). The main objective was to establish a long-term, instrumented field trial designed to evaluate the agronomic and environmental impacts of land application biosolids to bahiagrass pastures.

Biosolids (Class AA and B materials) were surface applied to the experimental area on April 2016, 2017, and 2018 and compared to nutrition provided with mineral fertilizers. Biosolids were applied either alone or in combination with biochar (a fine-grained carbon-rich residue produced through the pyrolysis of wood biomass) to supply an estimated rate of 160 lb plant available N/A/yr, which correspond to UF/IFAS high N option for established bahiagrass. During the 2017 and 2018 (currently underway), forage, water, and gas quality samples were collected and analyzed.

Results from 2017 indicated that addition of fertilizer (either as commercial N and P fertilizer or biosolids) increased annual bahiagrass herbage accumulation by an average of 68%; however, no difference between inorganic fertilizer vs biosolids treatments was observed.  Although inorganic fertilizer resulted in greater bahiagrass herbage accumulation in the first harvest, at the end of the growing season, greater bahiagrass herbage accumulation was associated with treatments receiving biosolids. This response was due to the slow release nature of nutrients present in biosolids. Similarly, no differences in bahiagrass crude protein and digestibility were observed among fertilizer and biosolids treatments. Results from this study indicated that biosolids application can supplement or replace inorganic fertilizer in bahiagrass pastures, with the added benefit of providing a more continuous supply of nutrients throughout the growing season.

During the 2017 growing season, application of biosolids (either alone or in combination with biochar) had no significant impact on water quality and greenhouse gas emissions. However, when bahiagrass received commercial inorganic fertilizer, large pulses of N and P were observed immediately after fertilizer application. Similar responses were also observed for nitrous oxide emissions. Greater nitrous oxide emissions were generally associated with the treatments receiving commercial fertilizer, particularly during the first few weeks following fertilization application. These results indicated that N and P losses associated with treatments receiving biosolids can be lower than commercial fertilizer. Results also indicated no potential benefit of biochar in reducing N and P losses. Forage and environmental data evaluations for the 2018 growing season are currently underway.



We thank H&H liquid disposal for their assistance obtaining and hauling the biosolids materials to the study site. We also want to extend our appreciation to the FCA for providing the funds to support this project.


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