Biochar impacts on nutrient dynamics in a subtropical grassland soil - Part 1. N and P leaching

Authors: LU, YANYAN - University Of Florida; SILVEIRA, MARIA - University Of Florida; O'CONNOR, GEORGE - University Of Florida; VENDRAMINI, JOAO - University Of Florida; ERICKSON, JOHN - University Of Florida; LI, YUNCONG - University Of Florida; Cavigelli, Michel

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/22/2020
Publication Date: 9/23/2020
Citation: Lu, Y., Silveira, M.L., O'Connor, G.A., Vendramini, J.M., Erickson, J., Li, Y., Cavigelli, M.A. 2020. Biochar impacts on nutrient dynamics in a subtropical grassland soil - Part 1. N and P leaching. Journal of Environmental Quality. 49:1408-1420. https://doi.org/10.1002/jeq2.20139.
DOI: https://doi.org/10.1002/jeq2.20139

Interpretive Summary: Concern about nutrient losses from biosolids applied to agricultural fields is restricting its use despite known agronomic benefits of biosolids application. In a 3-yr field study, researchers compared losses of nitrogen and phosphorus by leaching in an established perennial pasture in Florida following application of biosolids and inorganic fertilizers. Biosolids and fertilizer treatments were both applied with and without biochar, a material hypothesized to reduce nutrient leaching. Results showed that cumulative phosphorus leaching was negligible in all treatments and that nitrogen leaching was greater with inorganic fertilizers than biosolids. Biochar reduced nitrogen leaching from treatments receiving inorganic fertilizer by 60% but had no effect on phosphorus leaching. Results show that prudent nutrient management is possible with biosolids even in Florida soils with high water tables. These results will be of interest to policy makers, farmers, scientists, and others concerned about the impact of farm management on the environment.

Technical Abstract: Despite the numerous agronomic benefits of biosolids, concerns over nutrient (mainly N and P) losses restrict the extent that biosolids can be beneficially reused, especially in environmentally-sensitive Spodosols in Florida where water quality is a prominent concern. A 3-yr field study was designed to investigate the potential impacts of co-applying biochar with biosolids or inorganic fertilizer on N and P leaching losses. Nutrients were surface-applied as biosolids (aerobically digested Class B) and inorganic fertilizer (ammonium nitrate and triple superphosphate) to an established perennial pasture at equivalent annual rates typical of field practices. Biochar was applied at an annual rate of 20 Mg ha-1. Leachate N and P were monitored using passive-capillary drainage lysimeters installed in the center of each plot at a depth of 30 cm. Results demonstrated significant temporal variability in leachate N and P, with larger pulses generally occurring during periods of high water table levels or after intensive rainfall. Inorganic fertilizer generally resulted in greater leachate N and P losses than biosolids. No differences in leachate N and P losses between biosolids and control were observed. Approximately 1% of applied N was lost via leaching from biosolids treatments vs. 16% for inorganic fertilizer. Regardless of the P source, negligible (0.1 to 0.2% of applied P) cumulative P leaching occurred during the 3-yr study. Biochar had no effect on P leaching, but reduced N leaching from treatments receiving inorganic fertilizer by 60%. Prudent nutrient management is possible even on biosolids-amended Spodosols with high water tables.