Biochar enhancement of nitrification processes varies with soil conditions

Authors: Hale, Lauren; Hendratna, Aileen; Scott, Natalie; Gao, Suduan

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/9/2023
Publication Date: 5/13/2023
Citation: Hale, L.E., Hendratna, A., Scott, N.M., Gao, S. 2023. Biochar enhancement of nitrification processes varies with soil conditions. Science of the Total Environment. 887. Article 164146. https://doi.org/10.1016/j.scitotenv.2023.164146.
DOI: https://doi.org/10.1016/j.scitotenv.2023.164146

Interpretive Summary: Biochar has potential to reduce agronomic losses and groundwater pollution associated with applications of nitrogen (N) fertilizers in agriculture, but these benefits are inconsistent across varying biochar materials and soil conditions. This study methodically evaluated the impact of biochar soil incorporation on N transformation processes and underlying microbial mechanisms using soils with varying biochar types, soil texture, soil moisture, and manure compost co- amendments. We revealed that soil moisture was a critical factor affecting N transformation processes. Biochar offered some pH buffering potential, but the co-application of biochar with manure composts enhanced nitrification. Soil nitrifier populations tended to increase in response to a pinewood biochar, which was context dependent. Thus, growers and advisors should consider soil moisture and other environment conditions when incorporating biochar with the goal to reduce N losses.

Technical Abstract: Application of inorganic nitrogen (N) fertilizers in agriculture can increase emissions of nitrous oxide, a potent greenhouse gas, leaching of nitrate (NO3-), a groundwater contaminant hazardous to human health, and soil acidification. Biochar materials have been shown to impact the N transformation process that result in these losses and undesirable outcomes. However, there have been considerable inconsistencies in these reported impacts likely owing to variable physiochemical characteristics of the biochar materials and/or the soil environment. This study methodically evaluated the impact of biochar soil incorporation on N transformation processes and underlying microbial mechanisms using soils with varying biochar types, soil texture, soil moisture, and manure compost co- amendments. Laboratory incubations were conducted to monitor the fate of urea fertilizer N spiked in biochar amended and unamended soils by assaying soil ammonium (NH4+), nitrite (NO2-), and NO3- concentrations, pH, and abundances of soil nitrifiers; ammonia oxidizing bacteria and archaea (AOB and AOA) and Nitrospira with the capacity to perform complete ammonia oxidation (comammox). We revealed that soil moisture was a critical factor affecting N transformation processes, more so than biochar, but biochar did result in significantly different concentrations of N species in response to urea application. Biochar offered some buffering potential in the neutral-alkaline, unsaturated soils, preventing more than 1 unit drop in pH compared to unamended soils. Co-application of biochar with manure composts enhanced nitrification to some degree, which was evidenced by lower NH4+ and higher NO3-, and NO2- concentrations throughout the 7-week incubation and higher abundances of some soil nitrifiers at 4 weeks. Soil nitrifier populations tended to increase in response to a pinewood biochar, but trends differed for saturated soil, in soils of differing textures, or when different biochar materials were evaluated. Thus, when evaluating implications of biochar on the fate of mineral N fertilizer, soil moisture and other environment conditions should be considered.