Biochar and Manure Effects on Net Nitrogen Mineralization and Greenhouse Gas Emissions from Calcareous Soil under Corn

Few multiyear field studies have examined the impacts of a one-time biochar application on net N mineralization and greenhouse gas emissions in an irrigated, calcareous soil; yet this use of biochar is hypothesized as a means of sequestering atmospheric CO₂ and improving soil quality. We fall-applied four treatments: stockpiled dairy manure (42 Mg ha⁻¹ dry wt.), hardwood-derived biochar (22.4 Mg ha⁻¹), combined biochar and manure, and no amendments (control). Nitrogen fertilizer was applied in all plots and years based on treatment’s preseason soil test N and crop requirements and accounting for estimated N mineralized from added manure. From 2009 to 2011, we measured greenhouse gas fluxes using vented chambers, net N mineralization using buried bags, corn (Zea mays L.) yield, and N uptake, and in a succeeding year, root and shoot biomass and biomass C and N concentrations. Both amendments produced persistent soil effects. Manure increased seasonal and 3-yr cumulative net N mineralization, root biomass, and root/shoot ratio 1.6-fold, CO₂–C gas flux 1.2-fold, and reduced the soil NH₄/NO₃ ratio 58% relative to no-manure treatments. When compared with a class comprising all other treatments, biochar-only produced 33% less cumulative net N mineralization, 20% less CO₂–C, and 50% less N₂O-N gas emissions, and increased the soil NH₄/NO₃ ratio 1.8-fold, indicating that biochar impaired nitrification and N immobilization processes. The multi-year nature of biochar’s influence implies that a long-term driver is involved, possibly related to biochar’s enduring porosity and surface chemistry characteristics. While the biochar-only treatment demonstrated a potential to increase corn yields and minimize CO₂–C and N₂O-N gas emissions in these calcareous soils, biochar also caused decreased corn yields under conditions in which NH₄–N dominated the soil inorganic N pool. Combining biochar with manure more effectively utilized the two soil amendments, as it eliminated potential yield reductions caused by biochar and maximized manure net N mineralization potential.