Pedro Nunez

Nitrogen losses under different cattle grazing frequencies and intensities in a volcanic soil of Southern Chile.

Chilean livestock production systems have intensified over the last years, with increasing amounts of N fertilizer inputs creating the potentiality for environmental damage through N pollution of water and air, so that alternative production strategies have been developed to reduce such environmental impacts. This study assesses N losses under different grazing frequencies and intensities on permanent pasture (Lolium perenne L., Festuca arundinacea Schreb., Dactylis glomerata L., and Trifolium repens L.) on an Andisol in Southern Chile. Four grazing strategies were evaluated: frequent-heavy (FH), frequent-light (FL), infrequent-heavy (IH), infrequent-light (IL), and a no grazing control (C) treatment, and each with three replicates in a randomized complete block design. Results of the experiment indicate that N leaching losses were greater in the FH treatment (58.7 kg available N ha -1 ; p < 0.05) and with most of the leaching occurring in spring (39%). On average, N ammonia (NH3) losses were 10% greater in the frequent grazing treatments in relation to the infrequent grazing treatments, since there were no significant differences (P ≤ 0.05) among individual grazing events for FH, FL and IH. Results indicate that grazing frequency affects leaching losses while grazing intensity affects ammonia emissions from the grassland. Grazing with dairy cows in Southern Chile should consider this environmental constraint to ensure sustainable production over time.

MOVEMENT OF N0(3)-N AND NH4-N IN AN ANDISOL AND ITS INFLUENCE ON RYEGRASS PRODUCTION IN A SHORT TERM STUDY

En suelos acidos, el uso de fertilizantes amoniacales acelera los procesos de acidificacion y disminuye la produccion y persistencia de las pasturas. El nitrogeno (N) es el principal factor limitante del crecimiento vegetal en la mayoria de los sistemas agricolas, pero tambien es uno de los principales problemas ambientales del mundo. En Chile, no han sido reportados estudios sistematicos en el primer periodo de crecimiento de la pastura ni las perdidas de N por lixiviacion asociadas. Los objetivos de este estudio fueron: (i) evaluar el efecto de la fuente de N a dosis crecientes de aplicacion sobre el rendimiento y calidad de ballica (Lolium perenne) y (ii) cuantificar en el corto plazo las perdidas potenciales de N por lixiviacion y los cambios de pH a traves del perfil del suelo bajo condiciones de campo. Se realizo un experimento de campo durante la temporada primavera-verano 2000-2001 en un Andisol del Sur de Chile bajo riego. Se aplico urea y nitrato de sodio en dosis de 0, 150 y 300 kg N ha-1. La pastura fue cortada tres veces y se determino la produccion de materia seca (DM) y la concentracion de N foliar. Ademas, se determino el pH del suelo y las concentraciones de N-NH4+ y N-N03 para los 0-10 cm, 10-20 cm y 20-40 cm de profundidad, y se estimaron las maximas perdidas potenciales de N por lixiviacion. La produccion de DM aumento en 128 % a medida que el suministro de N se incremento de 0 a 300 kg N ha-1. La fuente de N no mostro ningun efecto sobre el rendimiento. La urea y el nitrato de sodio generaron una concentracion de N foliar mas alta a medida que la dosis de N aumento, y no se observo un efecto acidificante de la urea sobre la produccion de DM y la calidad de la pastura. La aplicacion de nitrato de sodio y urea (300 kg N ha-1) genero la mayor concentracion de N-NH4+ y N-N03 en las capas mas profundas del suelo. Para los 20-40 cm de profundidad, las maximas perdidas potenciales de N a traves del perfil del suelo fueron alrededor de 90 kg N ha-1 y correspondieron al periodo de menor tasa de crecimiento de la pastura

GRAZING MANAGEMENT, AMMONIA AND NITROUS OXIDE EMISSIONS: A GENERAL VIEW

The grazing management of grassland has a direct effect on nitrogen (N) recycling. This is an important reason why management has become an alternative to improve the grassland production and quality, in turn to make it more suitable for the environment. However, the livestock system intensification induces changes in the natural dynamics of the N cycle, accelerating gas emmisions (e.g. ammonia, NH3 and nitrous oxide, N2O) and leaching losses from soil under grazing. When the amount of N in the environment increases, there is an impact on smog episodes, global warming, stratospheric ozone depletion, acid rain and eutrophication of fresh water. There are different techniques to evaluate the gases emitted from the soil. This klonowledge is useful to design the strategies to reduce the negative consequences of theses gases on the environment. In this review, the effect of grazing managements on N gas emissions from soils and the current techniques for N gas emission measurements in the field and laboratories conditions are discussed.