"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.

Soil macrofauna in a Cerrado/Caatinga ecotone under different crops in Southwestern Piauí State, Brazil / Caracterização da macrofauna edáfica em ecótono Cerrado/Caatinga sob diferentes cultivos no Sudoeste piauiense

ABSTRACT: The aim of this study was to characterize the soil macrofauna under different crop systems and compare them to the macrofauna under the native vegetation of a Cerrado/Caatinga ecotone in southwestern Piauí State, Brazil. The areas studied included areas under sweetsop cultivation (Annona squamosa L.), andropogon grass with three years of use, andropogon grass with six years of use, pivot-irrigated corn, Napier grass, and native vegetation. In each area, soil layers of 0-0.1, 0.1-0.2, and 0.2-0.3m, including the surface litter, were evaluated following the Tropical Soil Biology and Fertility Program (TSBF) recommendations. The soil macrofauna from the different land-use systems were identified to the family level, and the mean density of each taxon was calculated for each soil-management type and layer. The structure of the soil macrofauna was negatively altered under the different crops in comparison to the native Cerrado/Caatinga vegetation, with macrofaunal occurrence varying in the different soil layers. A correlation existed between the functional groups and the soil grain-size distribution and moisture. Napier grass cultivation favored greater soil macrofaunal abundance, with a predominance of families belonging to the orders Isoptera and Hymenoptera. Number of soil macrofaunal families under pivot-irrigated corn was more like the number observed with the native vegetation, and corn also had greater family diversity compared to the other crops studied. Therefore, pivot-irrigated corn can reduce the impact of anthropogenic land use on the diversity of soil macrofauna.

RESUMO: Objetivou-se caracterizar a macrofauna edáfica sob diferentes cultivos comparando-os a vegetação nativa de ecótono Cerrado/Caatinga no Sudoeste do Piauí. As áreas estudadas foram: área sob cultivo de ata (Annona squamosa L.); capim andropogon com três anos de cultivo; capim andropogon com seis anos de cultivo; milho irrigado sob pivô; capim napier e vegetação nativa. Em cada área foram avaliadas as camadas de 0-0,1, 0,1-0,2 e 0,2-0,3m, inclusive a serapilheira de superfície, segundo recomendações do Tropical Soil Biology and Fertility Program (TSBF). A macrofauna edáfica nos diferentes sistemas de uso do solo foi identificada até o nível de famílias e a densidade média de cada táxon foi calculada para cada tipo de manejo do solo e camada. A estrutura da macrofauna edáfica foi alterada negativamente nos diferentes cultivos quando comparadas com a vegetação nativa de cerrado/caatinga, variando quanto a sua ocorrência nas diversas camadas de solo. Houve correlação entre os grupos funcionais com a distribuição granulométrica e umidade do solo. O cultivo de capim napier favoreceu maior abundância da macrofauna edáfica, porém com predominância das famílias pertencente às ordens Isoptera e Hymenoptera. O milho irrigado sob pivô apresenta número de famílias da macrofauna edáfica mais semelhante à vegetação nativa e maior diversidade de famílias em relação aos demais cultivos estudados, reduzindo o impacto do uso antrópico sobre a biodiversidade da macrofauna edáfica.