RESUMO

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.

RESUMO

Forest soils are N2O sources and commonly act as CH4 sinks. This study evaluated the dynamics of the CH4 and N2O fluxes of soils under Eucalyptus plantations and native Cerrado vegetation, as well as possible interactions between environmental factors and fluxes. The study was carried out in the Distrito Federal, Brazil, during 26 months, in three areas: in two stands of the hybrid Eucalyptus urophylla × Eucalyptus grandis, planted in 2011 (E1), and in 2009 (E2) and native Cerrado vegetation (CE). Measurements to determine the fluxes in a closed static chamber were carried out from Oct 2013 to Nov 2015. Soil and climate factors were monitored. During the study period, the mean CH4 fluxes were –22.48, –8.38 and –1.31 μg CH4 m–2 h–1 and the mean N2O fluxes 5.45, 4.85 and 3.85 μg N2O m–2 h–1 from E1, E2 and CE, respectively. Seasonality affected plantations in the studied sites. Cumulative CH4 influxes were calculated (year-1: –1.86 to -0.63 kg ha–1 yr–1; year-2: –1.85 to –1.34 kg ha–1 yr–1). Cumulative N2O fluxes in the three sites were ≤ 0.85 kg ha–1 yr–1. The change in land use from Cerrado to Eucalyptus plantations did not significantly changed regarding greenhouse gases (GHG), compared to the native vegetation. Flux rates of both gases (N2O and CH4) were low. Temporal variations in GHG fluxes and different ages of the stands did not cause significant differences in cumulative annual fluxes.

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RESUMO

Forest soils are N2O sources and commonly act as CH4 sinks. This study evaluated the dynamics of the CH4 and N2O fluxes of soils under Eucalyptus plantations and native Cerrado vegetation, as well as possible interactions between environmental factors and fluxes. The study was carried out in the Distrito Federal, Brazil, during 26 months, in three areas: in two stands of the hybrid Eucalyptus urophylla × Eucalyptus grandis, planted in 2011 (E1), and in 2009 (E2) and native Cerrado vegetation (CE). Measurements to determine the fluxes in a closed static chamber were carried out from Oct 2013 to Nov 2015. Soil and climate factors were monitored. During the study period, the mean CH4 fluxes were –22.48, –8.38 and –1.31 μg CH4 m–2 h–1 and the mean N2O fluxes 5.45, 4.85 and 3.85 μg N2O m–2 h–1 from E1, E2 and CE, respectively. Seasonality affected plantations in the studied sites. Cumulative CH4 influxes were calculated (year-1: –1.86 to -0.63 kg ha–1 yr–1; year-2: –1.85 to –1.34 kg ha–1 yr–1). Cumulative N2O fluxes in the three sites were ≤ 0.85 kg ha–1 yr–1. The change in land use from Cerrado to Eucalyptus plantations did not significantly changed regarding greenhouse gases (GHG), compared to the native vegetation. Flux rates of both gases (N2O and CH4) were low. Temporal variations in GHG fluxes and different ages of the stands did not cause significant differences in cumulative annual fluxes.(AU)

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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.

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Melon plants (Cucumis melo L.) are grown in the state of Rio Grande do Norte (RN), the largest producer of melons in Brazil, with plastic mulch and agrotextiles. Studies of crop evapotranspiration (ET) under these conditions are required to ensure adequate irrigation. This study aimed to determine the crop coefficients (Kc) of irrigated melon plants grown with mulch and agrotextiles in the region of Mossoró, RN, based on the Bowen Ratio Energy Balance (BREB) method. Two experiments were conducted at different times during the 2009/2010 season in a melon producing area (4°59'52" S, 37°23'09" W, and 54 m elevation) to define ET and Kc. Due to the plastic cover and reduced precipitation during the experiments, the Kc obtained by the BREB method was considered the basal Kc - KcbBREB. The results were compared with the Kcb from the FAO 56 Bulletin. There was close agreement between BREB and FAO ET measurements (12 % underestimation by the FAO method for the entire crop season), with sizeable differences only during the initial phenological stage. The mean KcbBREB values of the two field campaigns were 0.26, 0.96 and 0.63 for the initial, midseason and late stages, respectively. The high KcbBREB value in the initial growth phase may be related to the effect of the plastic mulch and agrotextiles on the energy balance at the surface. The relationship between KcbBREB and fc had high correlation, making possible an estimation of the melon Kcb based on the level of crop ground cover.

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RESUMO

Melon plants (Cucumis melo L.) are grown in the state of Rio Grande do Norte (RN), the largest producer of melons in Brazil, with plastic mulch and agrotextiles. Studies of crop evapotranspiration (ET) under these conditions are required to ensure adequate irrigation. This study aimed to determine the crop coefficients (Kc) of irrigated melon plants grown with mulch and agrotextiles in the region of Mossoró, RN, based on the Bowen Ratio Energy Balance (BREB) method. Two experiments were conducted at different times during the 2009/2010 season in a melon producing area (4°59'52" S, 37°23'09" W, and 54 m elevation) to define ET and Kc. Due to the plastic cover and reduced precipitation during the experiments, the Kc obtained by the BREB method was considered the basal Kc - KcbBREB. The results were compared with the Kcb from the FAO 56 Bulletin. There was close agreement between BREB and FAO ET measurements (12 % underestimation by the FAO method for the entire crop season), with sizeable differences only during the initial phenological stage. The mean KcbBREB values of the two field campaigns were 0.26, 0.96 and 0.63 for the initial, midseason and late stages, respectively. The high KcbBREB value in the initial growth phase may be related to the effect of the plastic mulch and agrotextiles on the energy balance at the surface. The relationship between KcbBREB and fc had high correlation, making possible an estimation of the melon Kcb based on the level of crop ground cover.(AU)

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RESUMO

O estudo conduzido no SIPA (Sistema Integrado de Produção Agroecológica), localizado no município de Seropédica-RJ, foi desenvolvido com o objetivo de gerar modelos para caracterizar a variação e evolução do índice de área foliar (IAF) e da biomassa total da cultura do pimentão em função dos graus-dias. A análise foi realizada em esquema de parcelas subdivididas no tempo, com 3 repetições. Os modelos matemáticos obtidos por regressão foram escolhidos em função da significância dos coeficientes do modelo, do valor de F da analise de variância e do maior coeficiente de determinação (R2). As curvas ajustadas do IAF e biomassa e seus respectivos valores máximos confirmam que a metodologia dos graus-dias é viável para determinação dos estádios fenológicos da cultura. Os sistemas de plantio convencional e direto não foram significativamente diferentes entre si, em relação ao índice de área foliar e biomassa da cultura do pimentão. Foram necessários 1533 GDA para a cultura completar o ciclo produtivo, obtendo-se o máximo acúmulo de biomassa aos 1059 e 1148 GDA nos sistemas de plantio convencional e direto, respectivamente.

This study was carried out at SIPA (Integrated Agroecological Production System), in Seropédica, RJ, Brazil, with the objective of generating models for characterizing variation and evolution of leaf area index (LAI) and total dry mass of Bell pepper as a function of degree days. Experimental design was of plots split in time, with three replications. The matematical models obtained by regression analysis on the basis of the significance of the coefficients, the F value in the variance analysis of regression, and higher determination coefficient (R2). Based on adjusted curves for LAI and dry mass and in their respective maximum values degree days is a viable methodology for determination of crop phenological stages. The values of LAI and biomass accumulated by the plants were not significantly different between tillage systems. Bell pepper needed a total of 1533 degree days for completing its productive cycle, with maximum dry mass accumulation occurring at 1059 and 1148 degree days for conventional and no till cropping, respectively.

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