Strategies for mitigating nitrous oxide emissions from soils fertilized with urea and cultivated with maize in the off-season in Southern Amazon

Abstract

Abstract Various strategies, particularly those that affect nitrogen-related process at the soil plant interface, have been investigated with the aim of reducing N2O emissions from soils fertilized with urea, the main nitrogen source employed in Brazilian agriculture. This study aimed to evaluate N2O emissions from soils cultivated with maize in soybean-maize succession following treatment with different mitigation approaches in Southern Amazon. An experiment of randomized block design was performed involving seven treatments in which maize was cultivated in soil: (T1) under control conditions; (T2) inoculated with nitrogen-fixing bacteria (NFB); (T3) fertilized with urea; (T4) inoculated with NFB and fertilized with urea; (T5) fertilized with urea containing the nitrification inhibitor dicyandiamide (DCD); (T6) fertilized with urea containing the urease inhibitor N-(n-butyl)thiophosphoric triamide (NBPT); (T7) fertilized with urea containing a combination of DCD and NBPT. The highest N2O fluxes (300 µg N2O-N m-2 h-1) were recorded for T3 and T4 around 12 to 14 days after top dressing fertilization with urea. Application of DCD-containing urea (T5 and, to a lesser extent, T7) was effective in reducing N2O emissions. Emission factors were below of 1% for all treatments, with the highest values (≤ 0.42%) recorded for T3, T4 and T6. Fertilization with urea containing DCD alone or in combination with NBPT (T5 and T7) reduced emission values by around 75% to the level registered for T2. Use of nitrification inhibitors represents an alternative for the mitigation of greenhouse gas emissions during the off-season maize cropping cycle in Southern Amazon.