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 Nitrous oxide (N2O) is a greenhouse gas that contributes substantially to global climate change. The N2O soil emissions have a large uncertainty because of its low atmospheric concentration levels and enormous spatial and temporal variability, which hinders its correct field measurement. For this reason, there are many papers focused on improving the N2O measurements in the field, which focus on different parts of the measurement process. However, no studies have focused on determining the appropriate method, in terms of simplicity and precision, for the sample extraction from inside of the chambers and its transfer to the storage vials, although this step is key in the sampling process. This study aimed to assess and compare the accuracies of three simple and economical methods in transfer soil emitted N2O from inside of the chambers to the vials. For this, a highly accepted method (vacuum by manual pump) and two simpler alternative methods (gas exchange by displacement and vacuum by syringe) were compared. Thirty static chambers were assessed with the quantified N2O emission values varied from 0 to 450 µg m-2 h-1 of N-N2O. Out of the three assessed methods, the vacuum method through the use of a manual vacuum pump was the best to quantifying N2O soil emissions (capturing 57 % of the highest emission values), followed by the gas exchange method by displacement (30 %), and finally by the vacuum method by syringe extraction (13%).

Nitrous oxide (N2O) is the main greenhouse gas (GHG) emitted from agricultural soils as a by-pass product of nitrification and denitrification processes. The Intergovernmental Panel on Climate Change (IPCC) excluded from its GHG inventory guidelines in 2006 the Nitrogen Biological Fixation (NBF) as a source of N2O emissions by crop legumes, due to the lack of solid scientific evidenceon the existence of these emissions. However, at present the actual amount of N2O emissions by crop legumes in the field is still under investigation, with special emphasis on soybeans which are is the main commodity produced by Argentina and a main biodiesel source. The influence of NBF on N2O emissions can be tested using non-nodulating soybean varieties. This study aims to compare and analyse N2O emissions from nodulating and non-nodulating soybean varieties in order to clarify the actual influence of this commodity on field GHG emissions. Gas samples were collected from closed non-vented chambers. N2O emissions ranged from -9 to +15 |ig N-N2O m-2 h-1 and only in the last sampling date, values differed significantly between treatments (non-nodulating > nodulating soybean). N2O emissions were positively related with soil N-NO3 concentration and soil water-filled pore space (WFPS). Results show that in this field study, NBF caused only a slight impact on N2O emissions. These results agree with the latest IPCC guidelines in 2006 for GHG inventories.

El óxido nitroso (N2O) es el principal gas de efecto invernadero emitido desde el sector agrícola y su producción biológica en los suelos se genera por dos vías, la nitrificación y la desnitrificación. Recientemente el Panel Intergubernamental para el Cambio Climático (IPCC) ha excluido de sus directrices de inventario a la Fijación Biológica del Nitrógeno (FBN) como fuente de emisión de N2O por los cultivos leguminosos, debido a la falta de evidencia segura sobre la existencia de estas emisiones. Pese a ello, en la actualidad se sigue discutiendo sobre la emisión de N2O real emitida desde los cultivos leguminosos a campo, en especial en soja que es el principal producto producido por la Argentina y fuente de biodiesel. La influencia de FBN sobre la emisión de N2O puede probarse utilizando variedades de soja no nodulante. El objetivo de este trabajo fue comparar y analizar la emisión de N2O desde suelos con cultivos de soja de variedad nodulante y no nodulante, con el fin de evaluar la influencia real del cultivo sobre la emisión de N2O a campo. Las muestras de gas fueron colectadas con cámaras cerradas no ventiladas. La emisión de N2O varió entre -9 y 15 |ig N-N2O m-2 h-1. Sólo se observó diferencia significativa en la emisión de N2O entre los tratamientos en la última fecha de muestreo (no nodulante > nodulante). La emisión de N2O se relacionó positivamente con la concentración de N-NO3- del suelo y con el espacio poroso lleno de agua (EPLLA). Esta ausencia de diferencia significativa en los valores de emisión de N2O entre los tratamientos, indica que la soja nodulante no emitió mayor cantidad de N2O que la no nodulante, revelando que la presencia de nódulos fijadores per se no afectó la cantidad de N2O emitida durante el crecimiento del cultivo de soja. Estos resultados avalan lo establecido por las últimas directrices de IPCC 2006 y ponen en cuestión otras metodologías de inventario que cargan más emisión de N2O a los cultivos de soja. Los resultados del presente estudio muestran que la FBN sólo causó un ligero impacto en la emisión de N2O, en concordancia con las últimas directrices del IPCC del 2006 para los inventarios de GEI.

O uso adequado de câmaras estáticas para determinar as emissões de N2O no campo requer a definição da hora do dia que melhor representa a taxa de emissão média diária. Um experimento de campo de curta duração foi realizado em um Chernossolo do Pampa Ondulado da Argentina, cultivado com soja em sistema plantio direto. As taxas de emissão de N2O foram medidas a cada 3 h durante três dias consecutivos. As taxas de emissão de N2O variaram entre 62,58 e 145,99 mg m-2 h-1 de N-N2O (média de cinco câmaras de campo) e foram negativamente relacionadas (R² = 0,34; p <0,01 ) com a temperatura do solo (14 - 20 °C). As taxas de emissão de N2O medidas entre 9 e 12 h foram positivamente relacionadas com a média diária (R² = 0,87; p <0,01), mostrando que na região de estudo a melhor época para amostragem de GEE é pela manhã.

The correct use of closed field chambers to determine N2O emissions requires defining the time of day that best represents the daily mean N2O flux. A short-term field experiment was carried out on a Mollisol soil, on which annual crops were grown under no-till management in the Pampa Ondulada of Argentina. The N2O emission rates were measured every 3 h for three consecutive days. Fluxes ranged from 62.58 to 145.99 ∝g N-N2O m-2 h-1 (average of five field chambers) and were negatively related (R² = 0.34, p < 0.01) to topsoil temperature (14 - 20 ºC). N2O emission rates measured between 9:00 and 12:00 am presented a high relationship to daily mean N2O flux (R² = 0.87, p < 0.01), showing that, in the study region, sampling in the mornings is preferable for GHG.