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

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.

Carbon Storage in Different Compartments in Eucalyptus Stands and Native Cerrado Vegetation.

This study evaluated Carbon (C) storage in different compartments in eucalyptus stands and native Cerrado vegetation. To determine C above ground, an inventory was carried out in the areas where diameter at breast height (DBH), diameter at base height (Db), and total tree height (H) were measured. In the stands, the rigorous cubage was made by the direct method, and in the native vegetation, it was determined by the indirect method through an allometric equation. Roots were collected by direct method using circular monoliths to a depth of 60 cm and determined by the volume of the cylinder. Samples were collected up to 100 cm deep to estimate C stock in the soil. All samples collected directly had C determined using the CHNS elemental analyzer. Gas samples were collected using a manually closed chamber, and the gas concentration was determined by gas chromatography. The results indicate high C storage in the studied areas > 183.99 Mg ha-1, could contribute to CO2 mitigation > 674.17 Mg ha-1. In addition to low emissions (<1 kg ha-1 yr-1) for the three evaluated areas, with no statistical difference in relation to the Global Warming Potential. Concerning the native cerrado vegetation conversion, the "4-year-old eucalyptus stand" seemed to restore the original soil carbon stocks in the first-meter depth, regardless of some losses that might have occurred right after establishment. Conversely, a significant loss of carbon in the soil was observed due to the alternative setting, where similar natural land was converted into agriculture, mostly soybean, and then, years later, turned into the "6-year-old eucalyptus stand" (28.43 Mg ha-1). Under this study, these mixed series of C baselines in landscape transitions have reflected on unlike C dynamics outcomes, whereas at the bottom line, total C stocks were higher in the younger forest (4-year-old stand). Therefore, our finding indicates that we should be thoughtful regarding upscaling carbon emissions and sequestration from small-scale measurements to regional scales.

Effect of soil tillage and N fertilization on N2O mitigation in maize in the Brazilian Cerrado.

The management system of soils and nitrogen application can cause impacts on the N2O emissions produced by the agricultural sector. In the establishment of practices of greenhouse gas mitigation for this sector, the objective of this study was to evaluate the effect of soil tillage, with and without N fertilization, on N2O emissions from Oxisols under rainfed maize in the Brazilian Cerrado region. The managements were of monoculture maize under conventional tillage (CT) and no-tillage (NT), with (1) and without (0) application of N fertilizer (0 and 257 kg N ha-1). From November 2014 to October 2015, gas emissions were measured. The soil and climate variables were measured and related to the N2O fluxes. In the N-fertilized treatments, N2O fluxes were higher (P < 0.01), ranging from -21 µg m-2 h-1 to 548 µg m-2 h-1 N2O under conventional tillage and from -21 µg m-2 h-1 to 380 µg m-2 h-1 N2O under no-tillage, compared with -6 to 93 µg m-2 h-1 N2O from systems without N application. There was a combined effect of mineral N and water-filled pore space for most N2O fluxes. The emission factors of N2O during maize cultivation were lower than the standard factor (1%) established by the International Panel of Climate Change. During the plant crop cycle, 30% less N2O was emitted from the N-fertilized no-tillage than from the conventional tillage. For the total cumulative N2O (crop cycle + fallow), the N2O emissions from NT1 and CT1 were not different, but 10× higher than those from the respective crops without N fertilization. To the emissions per unit of grain yield, CT1 and NT1 emitted 769 and 391 mg N2O kg-1 grain produced, respectively, and NT1 was most efficient in fertilizer-into-product conversion. Under maize cultivation, the soil acted as N2O source, regardless of the management.