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 CO 2 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, CO 2 –C gas flux 1.2‐fold, and reduced the soil NH 4 /NO 3 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 CO 2 –C, and 50% less N 2 O‐N gas emissions, and increased the soil NH 4 /NO 3 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 CO 2 –C and N 2 O‐N gas emissions in these calcareous soils, biochar also caused decreased corn yields under conditions in which NH 4 –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.