Grazing intensities and season affect N^sub 2^O emissions in a tropical pastureland

• Published in: Journal of animal science Vol. 94; p. 312
• Main Authors: Cardoso, A S, Brito, L F, Janusckiewicz, E R, Morgado, E S, Barbero, R P, Koscheck, J F W, Reis, R A, Ruggieri, A C
• Format: Journal Article
• Language: English
• Published: Champaign Oxford University Press 01.10.2016
• Subjects: Autumn; Data processing; Emission measurements; Emissions; Fertilizers; Fluxes; Grasslands; Grazing; Greenhouse gases; Interpolation; Nitrous oxide; Pasture; Rainfall; Seasons; Spring (season); Statistical analysis; Stocking rates; Summer; Urea; Variance analysis
• ISSN: 0021-8812; 1525-3163
• DOI: 10.2527/jam2016-0653

The study assessed a tropical pasture in Brazil to determine how grazing height and season influences N2O production and consumption. Nitrous oxide fluxes were measured over 2 yr in a Marandu palisade grass pasture with 3 grazing heights (15, 25, and 35 cm), 6 replicates, and 4 seasons (spring, summer, autumn and winter) using static closed chamber and chromatography quantification. The N2O flux (µg N2O-N m-2 h-1) was integrated by linear interpolation to cumulative emissions. The patters of N2O fluxes were displayed by using means and SEM. The data were submitted to ANOVA by using R statistical software. When significant, a polynomial orthogonal contrast was done. Nitrous oxide emissions were maximum following rainfall events and application of urea fertilizer (Fig. 1). Nitrous oxide emissions were greatest in the summers whereas lower fluxes associated with frequent instances of N2O uptake in other seasons. The topmost rate of N2O emissions was measured in the second week of December 2013 when mean fluxes were 469, 394, and 279 µg N2O-N m-2 h-1 for 15, 25, and 35 cm of pasture heights, respectively. Negative fluxes were detected in approximately 60% of all N2O sampling especially in the spring and autumn of the yr 2 when lower values of water-filled pore space were also recorded. The highest rate of N2O consumption was measured on May 23, 2014, when mean fluxes were -299, -235, and -287 µg N2O-N m-2 h-1 for pastures heights of 15, 25, and 35 cm, respectively. Grazing intensity was significantly correlated with N2O flux during the summer. There was a linear reduction in annual cumulative N2O emissions (P < 0.05) with decreasing grazing intensities for both years. The total N2O emissions were 300.1, 41.6, and -48.3 mg N2O-N m-2 in yr 1 and -153.2, -263.7, and -298.7 mg N2O-N m-2 in yr 2 for 15, 25, and 35 cm of pasture heights, respectively. The greater grazing intensity had the highest levels of N2O emissions in all seasons except for in the spring of yr 1. The grassland intensity on cumulative N2O emissions was negatively linear in the annual analysis (P < 0.05) driven by the negative associations observed in the summer (P < 0.05) and even more so in the autumn (P < 0.001). There was a negative linear effect of pasture height on the amount of N2O emitted/consumed. High stocking rates in the grazing systems influenced the increment of N2O production, although lower grazing intensities contributes to N2O mitigation in tropical pastures.