Biochar and coal char mitigate nutrient and dissolved organic carbon loss from liquid manure amended soils

Authors: COOPER, JENNIFER - University Of Nebraska; DRIJBER, RHAE - University Of Nebraska; MALAKAR, ARINDAM - University Of Nebraska; Jin, Virginia; Miller, Daniel; KAISER, MICHAEL - University Of Nebraska

Submitted to: Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/3/2022
Publication Date: 1/19/2022
Citation: Cooper, J.A., Drijber, R., Malakar, A., Jin, V.L., Miller, D.N., Kaiser, M. 2022. Biochar and coal char mitigate nutrient and dissolved organic carbon loss from liquid manure amended soils. Environmental Quality. 51(2):272-287. https://doi.org/10.1002/jeq2.20327.
DOI: https://doi.org/10.1002/jeq2.20327

Interpretive Summary: This research explored the potential for biochar or char to decrease nutrient losses and change soil microbial communities in soils amended with livestock manure (dairy or swine slurry). A 105-day greenhouse pot experiment was used to test char or biochar effects on two soils (silt loam, sandy loam) where field corn was grown in all pots. Both biochar and char decreased losses of dissolved organic carbon and phosphate, but only char application increased nitrate leaching. Biochar-amended soils retained up to three times more nitrate and produced higher corn biomass than non-amended soils. Biochar and char additions increased soil respiration only in silt loam soils following plant harvest, and only char addition decreased respiration in sandy loam soils. In both soils, soil bacterial and fungal abundance decreased when biochar or char was added. This study showed that adding biochar or char to manure-amended soils can decrease leaching of carbon and phosphorus from agricultural systems, and possibly retain nitrogen within the soil for plant use in the next growing season. Overall, these results suggest that adding biochar or char can help decrease environmental pollution while also boosting crop growth in manure-amended cropping systems.

Technical Abstract: Leaching of nitrate into groundwater due to agricultural production is a rapidly growing global health concern. Mitigation strategies include the use of slower acting organic fertilizers, such as animal manure slurries, rather than faster acting synthetic fertilizers that are more easily leached. To further increase nutrient retention after slurry application, adding long-lasting organic amendments (i.e. char, biochar) to improve soil structure has gained increasing attention over the last decade. However, for large-scale adaption adoption of this combined approach, interactive effects between slurry application and structural improvement of differently textured soils on nutrient losses in gaseous and aqueous forms need to be clarified. Therefore, we examined the effects of two carbon rich materials, biochar and a coal combustion residue (char), on manure-amended soils (dairy or swine slurry; silt loam or sandy loam) by evaluating potential losses of soil carbon, nitrogen, and phosphorus as well as changes to microbial biomass. Both biochar (0.6-27%) and char (1.6-36%) reduced leaching of dissolved organic carbon (DOC) independent of soil texture and type of slurry. Biochar (15-24%) and char (38-50%) reduced PO43- leaching in the silt loam only. We found that N leaching increased from char application, but was unaffected by biochar. Char reduced CO2 emissions from the sandy loam by 9.7-54%, while both biochar and char increased CO2 emissions in the silt loam by 38-48% during plant root senescence. Bacterial and fungal biomass decreased when biochar and char were added. Post-experiment soils containing biochar retained up to three times more NO3- and produced higher plant biomass than control soils. Depending on soil characteristics, biochar and char have the potential to reduce PO43- and DOC leaching, while biochar may aid in retention of nutrients for subsequent growing seasons.