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.

The aim of our work was to evaluate the effects of different forestry residue managements of Pinus taeda (L) on different soil phosphorus (P) fractions and total organic carbon (TOC) in an Ultisol, belonging to the great group of Kandiudult, in Misiones province. The experiment consisted of the following treatments: 1) without residues: residue and forest floor extraction - Pinus taeda plantation; 2) burning: prescribed forestry residue burning and soil dragging - P. taeda plantation; 3) direct plantation: forestry residue conservation - P. taeda plantation and 4) secondary forest: forestry residue conservation without plantation - growth of natural forest. Soil samples were taken at 0-5 and 5-15 cm after six and nine years of treatment application. TOC and the Hedley P fractionation was carried out. Residue extraction was the treatment that presented the most negative effect on available and moderately available organic P at the topsoil, associated with the lesser content of TOC. The burning treatment did not affect adversely TOC in the topsoil, but a larger P adsorption was observed after six years indicating a reduction in P availability. There was no effect of the different treatments on total P at both depths. Taking into account these results, conservation of superficial forest residues is an appropriate management practice to preserve and improve TOC and organic P in these soils.

El objetivo de este trabajo fue evaluar los efectos de diferentes sistemas de manejo de residuos de cosecha en una plantación de Pinus taeda (L) sobre las distintas fracciones de fósforo (P) del suelo y el carbono orgánico total (COT), en un suelo Kandiudult de la provincia de Misiones, con el fin de establecer estrategias de manejo para el mantenimiento y la mejora de estas variables en sistemas forestales. Se realizó un ensayo con los siguientes tratamientos: 1) Sin Residuos: extracción de residuos y mantillo - plantación con Pinus taeda; 2) Quema: quema de residuos y rastra - plantación con P. taeda; 3) Plantación Directa: conservación de residuos de la cosecha - plantación con P. taeda y 4) Capuera: conservación de residuos - desarrollo del bosque secundario. A los seis y nueve años de aplicados los tratamientos se muestreó a dos profundidades (0-5 cm y 5-15 cm), se evaluó el COT y se realizó el fraccionamiento secuencial de P de Hedley. El manejo que presentó el mayor impacto negativo sobre el P orgánico, tanto lábil como moderadamente lábil en la capa superficial del suelo, fue la extracción total de residuos, asociado a las menores concentraciones de COT en este tratamiento. La quema no afectó negativamente al COT en la capa superficial del suelo. Sin embargo, se observó una mayor adsorción de P a los seis años, indicando una menor disponibilidad de dicho nutriente. No se observó efecto de los tratamientos sobre el P total en ambas profundidades y años estudiados. Según los resultados obtenidos, la conservación superficial de los residuos forestales resultó ser una práctica de manejo apropiada para preservar y mejorar el COT y el P orgánico en estos suelos.