"Effects of soil management, rotation and sequence of crops on soil nitrous oxide emissions in the Cerrado: A multi-factor assessment"

Abstract

The emission of nitrous oxide (N₂O), one of the main greenhouse gases, which contributes significantly to global warming, is a major challenge in modern agriculture. The effects of land use systems on N₂O emissions are the result of multiple variables, whose interactions need to be better understood. In this sense, this study analyzed the possible effects of different soil managements, crop rotations and sequences, as well as edaphoclimatic factors causing N₂O emissions from soils in the Cerrado biome (scrubland). The following four land-use systems were evaluated: 1) No-tillage cultivation with biennial crop rotations and sequences: legume-grass and alternating grass-legume crops in the second season - NT-SS/MP; 2) No-tillage with biennial rotations and sequences: grass-legume and alternating second crop of legume-grass - NT-MP/SS; 3) Conventional planting with disc harrow and biennial legume-grass rotation-CT-S/M; and 4) Native Cerrado (CE), no agricultural land use. The legume and grass species, planted in the two no-tillage treatments were soybean, followed by sorghum BRS3.32 (Sorghum bicolor (L.) Moench) (SS), and maize, followed by pigeon pea (Cajanus cajan) (MP). Nitrous oxide emissions were evaluated for 25 months (October 2013 to October 2015), and the results were grouped in annual, total, growing and non-growing seasons, as well as yield-scaled N₂O emissions. The mean N₂O fluxes were 24.14, 15.71, 32.49 and 1.87 μg m^-2 h^-1 in the NT-SS/MP, NT-MP/SS, CT-S/M and Cerrado areas respectively. Cumulative N₂O fluxes over the total evaluation period from the systems NT-SS/MP, NT-MP/SS, CT-S/M and CE, respectively, were 3.47, 2.29, 4.87 and 0.26 kg ha^-1. A correlation between N₂O fluxes and the environmental variables was observed, with the exception of water-filled pore space (WFPS), but N₂O peaks were associated with WFPS values of >65%. In the 2014-2015 growing season, yield-scaled N₂O emissions from NT-MP/SS were lower than from CT-S/M. A multi-factor approach indicated that conventional management with main season soybean or maize and no alternating crop sequence intensifies soil N₂O emissions in the Cerrado.

Keywords: GHGs emissions; Maize; N fertilization; Soybean; Tillage system.