ABSTRACT Increasing the use of nitrogen (N) fertilizers will be necessary to enhance grain and pasture yields to satisfy the growing world demand for food. Organic amendments, such as farm dairy effluents (FDE), are an alternative to traditional synthetic fertilizers. However, part of the applied N could be lost as ammonia (NH3) volatilization or nitrous oxide (N2O) emission, decreasing N availability to plants. Nitrification inhibitors, such as dicyandiamide (DCD), suppress the microbial process of nitrification, decreasing soil nitrate concentration and, therefore, N2O emission. Reducing N2O losses from agricultural soils is a key subject for sustainable production. This research aimed to quantify the effect of DCD addition to the FDE on the emissions of N2O and the volatilization of NH3 from the soil. A field trial was carried out in which NH3 volatilization and N2O emission were measured over 49 days after applying FDE, FDE with DCD (DCD), and control (C, without N added) treatments. The amount of N applied as FDE was 120 kg of N ha-1. Accumulated N2O emission during the 49 days after the application was 526, 237, and 174 g N2O-N ha-1 from the soil in the FDE, DCD, and C treatments, respectively. No significant differences were observed in accumulated NH3 volatilization. Pasture yield was higher in DCD treatment, followed by C and FDE. Under low temperatures and high soil moisture conditions, adding DCD to the FDE could be considered an effective alternative to increase pasture yields, decrease N2O emissions, and maintain NH3 volatilization, reducing total N losses to the atmosphere by about 14 %. Adding DCD to the FDE is a promising alternative for the more efficient N use of farm dairy effluents as fertilizer to mitigate N losses, tending to reduce N losses as N2O emissions. More studies are necessary to verify the result of using FDE + DCD under different soils and climates. (N food amendments , (FDE) However NH (NH3 NO O (N2O plants inhibitors (DCD) nitrification therefore production 4 C, (C added treatments 12 ha1. ha1 ha 1. 1 526 237 17 N2ON NON ha- respectively treatment conditions % climates (FDE (NH (DCD 52 23 ON 5 2

RESUMEN El aumento de las fuentes de fertilización será necesario para satisfacer la creciente demanda de alimentos en todo el mundo. Por este motivo, las enmiendas orgánicas surgen como una alternativa a los fertilizantes sintéticos. El compostaje de residuos orgánicos estabiliza el contenido de nitrógeno (N) y retrasa la liberación de N al suelo. La aplicación de enmiendas compostadas al suelo podría reducir las pérdidas de N, incluido el óxido nitroso (N2O), un gas de efecto invernadero con gran potencial de calentamiento global. El objetivo de este trabajo fue evaluar la emisión de N2O desde un suelo Argiudol típico luego de aplicar un fertilizante sintético tradicional, guano de ave crudo y compostado y un suelo control. Las tasas emisión de N2O acumuladas durante los 32 días que duro el ensayo fueron 1273, 965, 423 y 244 g de N2O-N ha-1 desde el suelo con aplicación de urea, guano de ave, compost de guano de ave y control, respectivamente. Nuestros resultados sugieren que la aplicación de compost de guano al suelo produce menores emisiones de N2O que la aplicación de guano de ave crudo o de urea. La presencia de compuestos más estabilizados en el compost de guano disminuye la disponibilidad de nitrato del suelo.

ABSTRACT Diversification in fertilizer sources will be necessary to meet the growing demand for food worldwide. For this reason, organic amendments emerge as a synthetic fertilizers alternative. Composting organic waste stabilizes the nitrogen (N) content and delays N release to the soil. Applying composted amendments to the soil could reduce the losses of N, including nitrous oxide (N2O), a greenhouse gas with great potential for global warming. The objective of this work was to evaluate the N2O emission in typical Argiudol soil after applying a traditional synthetic fertilizer, raw poultry manure, composted poultry manure and control soil. Cumulative N2O emission rates during the 32 days of the trial were 1273, 965, 423, and 244 g N2O-N/ha-1 from the soil using urea, poultry manure, composted poultry manure, and control, respectively. Our results suggest that the application of composted poultry manure to the soil produces lower N2O emissions than the application of raw poultry manure or urea. The presence of more stabilized compounds in the composted manure decreases the soil nitrate availability.

ABSTRACT South America covers a vast area with diverse climates and landscapes, with high participation in the global production of food and fibers. It is crucial to understand the risks, vulnerabilities, and opportunities that climate change brings to this region. We analyzed the increasing tension between agribusiness models and smallholder models, the risks, opportunities, and main adaptation measures that can be adopted in the agricultural sector of the South American countries facing climate change. This study is a review of adaptation actions in the agricultural sector for the different regions of South America. Vulnerability exists, firstly, because rural populations are exposed in many of the countries, often with high rates of poverty and low rates of socioeconomic development. Concerning the adaptation measures already taken, there are numerous cases of interventions by national, provincial, and municipal states for planned measures. Farmers are very active in adopting autonomous measures. Many adaptation measures show co-benefits with climate change mitigation or the prevention of land degradation and desertification, but other adaptation measures do not go in this direction. In the forthcoming times, the region’s rich natural resources are going to be subjected to strong market pressures and climate change threats. It is key to generate strategies for the care of these resources for their permanence for future generations.

Um dos benefícios esperados do uso do plantio direto é um maior sequestro de C. Contudo, nem sempre se observa maior retenção de C no solo quando esse sistema de preparo é utilizado, devido principalmente às diferenças em tipo de solo e conteúdo inicial de C, entre outras. O objetivo deste trabalho foi avaliar o potencial do plantio direto para estocar C orgânico nos solos da Região do Pampa Argentino. Foram coletadas amostras de solo em 40 áreas sob plantio direto ou preparo convencional e em sete campos não cultivados por vários anos. Determinaram-se o C orgânico total, N total, suas frações lábeis, sua taxa de estratificação e a capacidade de estocar C dos solos sob diferentes manejos, na camada de 0-30 cm de profundidade, a qual foi dividida, para fins de amostragem, em três profundidades (0-5, 5-15 e 15-30 cm). Verificou-se diferença significativa (p < 0,05) para todos os pools de C entre os solos não cultivados e os cultivados. A diferença mais pronunciada foi verificada na camada superficial (0-5 cm), sendo determinado o maior teor de C lábil próximo da superfície do solo (não perturbado > plantio direto > preparo convencional). A taxa de estratificação do C lábil (0-5/5-15 cm) permitiu separar as áreas sob plantio direto daquelas sob preparo convencional. Boa parte da variação em C potencialmente mineralizável foi explicada pela fração lábil do C (R² = 0,61), assim como pelo C orgânico total (R² = 0,67). Os solos sob plantio direto não estocaram mais C orgânico do que os preparados de maneira convencional, na camada de 0-30 cm. Entretanto, houve substancial estratificação dos pools de C lábil nos locais sob plantio direto, indicando que, se a taxa de estratificação for realmente um indicador de qualidade de solos, as áreas sob plantio direto poderiam ter maior potencial de acúmulo de C, pelo menos nas camadas superficiais de solo, se comparada com as áreas sob preparo convencional. O C orgânico particulado e o C potencialmente mineralizável podem ser utilizados para avaliar variações na matéria orgânica da camada superficial do solo.

One of the expected benefits of no-tillage systems is a higher rate of soil C sequestration. However, higher C retention in soil is not always apparent when no-tillage is applied, due e.g., to substantial differences in soil type and initial C content. The main purpose of this study was to evaluate the potential of no-tillage management to increase the stock of total organic C in soils of the Pampas region in Argentina. Forty crop fields under no-tillage and conventional tillage systems and seven undisturbed soils were sampled. Total organic C, total N, their fractions and stratification ratios and the C storage capacity of the soils under different managements were assessed in samples to a depth of 30 cm, in three layers (0-5, 5-15 and 15-30 cm). The differences between the C pools of the undisturbed and cultivated soils were significant (p < 0.05) and most pronounced in the top (0-5 cm) soil layer, with more active C near the soil surface (undisturbed > no-tillage > conventional tillage). Based on the stratification ratio of the labile C pool (0-5/5-15 cm), the untilled were separated from conventionally tilled areas. Much of the variation in potentially mineralizable C was explained by this active C fraction (R² = 0.61) and by total organic C (R² = 0.67). No-till soils did not accumulate more organic C than conventionally tilled soils in the 0-30 cm layer, but there was substantial stratification of total and active C pools at no till sites. If the C stratification ratio is really an indicator of soil quality, then the C storage potential of no-tillage would be greater than in conventional tillage, at least in the surface layers. Particulate organic C and potentially mineralizable C may be useful to evaluate variations in topsoil organic matter.

Neste experimento avaliou-se o carbono da biomassa microbiana do solo (C-BMS) em diferentes solos sob topossequência de pastagem e a viabilidade de utilizar amostras condicionadas na forma de terra fina seca ao ar (TFSA). Observou-se para C-BMS, separação dos conteúdos entre os diferentes tipos de solo. A época de inverno favoreceu a C-BMS, elevando-se em 60% em relação ao verão. Na comparação realizada entre os solos preparados na forma de TFSA e com a metodologia de fumigação-extração não se detectou diferença significativa, encontrando-se correlações significativas para os dois métodos de preparo das amostras, o que estabelece um panorama promissor no uso desta metodologia, embora seja necessário maior aprofundamento neste aspecto.

In this experiment we evaluated microbial biomass carbon (C-SMB) from different soils under toposequences of pasture and the viability of the use of air dried soil samples (ADSS). C-SMB showed separation of values between different soil types. Winter season favored C-SMB being 60% higher in relation to summer. In comparison between the two soil sample preparation methods, ADSS and the classical one, there was no statistical. Significant correlations were observed between the two methods. This gives a positive perspective to the use of this new approach, even thought more study is necessary.