Seasonality and crab activity affects the nutrients and physicochemical parameters in mangrove soils, thus, affecting the emissions of greenhouse gases, such as nitrous oxide (N₂O). Climate change may intensify rainfall and/or enhance droughts, affecting mangroves and associated biota. Crabs are natural soil bioturbators responsible for soil aeration and turnover. We evaluated the effect of Ucides cordatus crab on N₂O emissions from mangrove soils under a semiarid climate in Northeastern Brazil. Soil and gas samples were collected over the rainy and dry seasons in crab-naturally-bioturbated and crab-exclusion mangrove plots. We measured the soil’s pH, redox potential, and the total contents of carbon, nitrogen, and sulfur. We found higher N₂O emissions in the crab-exclusion sites compared to the bioturbated sites, as well as higher N₂O emissions in the rainy season compared to the dry season. The fluxes of N₂O (µg m⁻² h⁻¹) were 47.3 ± 9.7 and 8.9 ± 0.5 for the crab-exclusion sites, and 36.5 ± 7.8 and 4.5 ± 2.1 for the bioturbated sites (wet and dry seasons, respectively). The soil turning over by macrofauna led to lower N₂O fluxes in natural crab-bioturbated areas, and seasonality was the environmental factor that contributed the most to the changes in N₂O emissions. Broadly, anthropic activities and seasonality influence nitrogen fate, N₂O emissions, and ecological services in coastal ecosystems.

The sugarcane (Saccharum spp. L.) mechanical harvesting system leaves a large amount of straw mulch on the soil surface. The straw mulch may affect soil conditions, root regrowth, and sugarcane yield. Thus, this study assessed the response of sugarcane root system growth and stalk yield to different rates of straw removal. An experiment was conducted in a Rhodic Kandiudox with sand clay loam texture to test the impact of four rates of straw removal: no removal (18.9 Mg ha⁻¹ of dry mass); moderate removal (8.7 Mg ha⁻¹); high removal (4.2 Mg ha⁻¹) and total removal on sugarcane root system and stalk yield. Higher concentrations of roots (60%) were found in the first 40 cm of soil. Moderate straw removal resulted in higher root mass (3.6 Mg ha⁻¹) and stalk production (23 Mg ha⁻¹ of dry mass). However, no straw removal reduced root mass by 20% (105 Mg ha⁻¹). Through regression analysis, it was estimated that retaining between 8.5 and 13 Mg ha⁻¹ of straw resulted in the highest root mass and stalk yield. Managing straw removal to retain a moderate amount enables producers to sustain suitable soil conditions for sugarcane root growth and stalk production while providing straw for industrial use.

Soil organic matter affects physical, chemical and biological conditions, and has been used as a soil quality index to differentiate the effects of different land uses and management practices. The objective of this study was to evaluate soil stocks of C and N under different land uses (conventional-tillage cropping, integrated crop-livestock system, and permanent pasture). The study area was located at the Institute of Animal Science in the municipality of Nova Odessa, São Paulo State (Brazil), with soil classified as Typic Acrudox with medium texture. Land use systems were: (1) integrated crop-livestock with maize and Urochloa brizantha cv. Marandu; (2) integrated crop-livestock with maize and U. ruziziensis; (3) integrated crop-livestock with maize and U. brizantha cv. Piatã; (4) long-term (25-yr-old) pasture with U. brizantha; and (5) conventional-tillage cropping with– maize only. The results showed that (to the layer 0-40 cm depth) the integrated crop-livestock systems (ICLS) had greater soil organic C (52.4 Mg ha-1) and N (4.3 Mg ha-1) than cropping (46.5 Mg C ha-1 and 4.0 Mg N ha-1) only or pasture only (47.6 Mg C ha-1 and 3.9 Mg N ha-1). The rotation with U. brizantha cv. Piatã had lower soil organic C (48.5 Mg ha-1) and N (3.9 Mg ha-1) than with U. brizantha cv. Marandu (56.2 Mg C ha-1 and 4.5 Mg N ha-1) and U. ruziziensis (56.6 Mg C ha-1 and 4.6 Mg N ha-1). These results suggest that integrated crop-livestock systems can be used to improve soil organic matter, and may have additional benefits in sustaining agricultural production in areas experiencing degradation from continuously grazed pastures.

A maior produção brasileira de mamona (Ricinus communis L.) se concentra na caatinga do estado da Bahia, onde a mudança do uso da terra para o seu cultivo tem sido considerada uma estratégia de recuperação de áreas degradadas. No entanto, alterações no solo nativo proporcionam impactos ambientais, como emissões de gases de efeito estufa (GEE). Presume-se que elevadas emissões de GEE sejam provenientes da mudança do uso da terra para o cultivo de mamona e que os subprodutos dessa oleaginosa também participam dessas emissões. O objetivo deste trabalho foi realizar o inventário das emissões de GEE decorrentes do cultivo da mamona e seus subprodutos. Foi realizado um estudo na Fazenda Floresta, no município de Irecê (BA), onde foram avaliadas: a mudança no estoque de carbono (C) no solo cultivado com mamona e na floresta nativa local; a quantidade de folhas senescentes e fitomassa epígea; e as emissões de GEE provenientes dos subprodutos da produção agrícola de mamona. Os resultados mostraram que a soma das folhas senescentes e fitomassa epígea obtida pela poda da mamona é superior a 1,6 Mg ha^-1ano^-1 e o uso da torta de mamona no solo apresentou emissões de N₂O próximas a 600 µg m^-2. As emissões provenientes do uso do biodiesel de óleo de rícino representaram menos de 10% das emissões. A mudança de uso da terra foi responsável pelas elevadas emissões de GEE, representando 87% do total em CO₂eq. Em comparação às emissões estimadas para o etanol de cana-de-açúcar, o biodiesel de mamona apresentou emissões 32% inferiores.