PSXII-17 The Effects of N Fertilization on N2O Emissions from Urine or Fecal Samples from Nellore Bulls

Abstract Better understanding of N2O emissions from interactions between urine or feces, with different levels of nitrogen (N) fertilization on tropical pastures would be helpful in developing strategies to mitigate emissions and improve N2O inventories. The objective of this study was to evaluate N2O emissions from feces or urine samples collected from Nellore young bulls, isolated or in association with different levels of N fertilizer. Study was designed as completely randomized block design with five replications per treatment. Treatments were two levels of excreta (Feces or Urine) and three levels of N fertilizer (0, 75 and 150 kg N ha-1). Ammonium nitrate was used as source of N (32% of N). One liter of urine or 1.5 kg of feces was used per chamber with the respective N dose directly applied on excreta sample. Gas emissions were evaluated using the static chamber closed method and quantified using gas chromatography. Chambers were closed for 40 min and gas samples were collected at 0, 20 and 40 min. After treatment imposition, gas was sampled three times during week 1, twice during week 2, 3, and 4 and once during week 5, 6, 7 and 8, and subsequently every 2 weeks for two consecutive years. Type of excreta samples did not affect N2O emissions. Additionally, associative effects of N fertilizer onto feces or urine was similar. Cumulative N2O emissions linearly increased with increasing levels of N regardless of source, and ranged from 5.95, 32.1 to 74.7 mg of N2O/m2, for 0, 75 and 150 kg/ha/year of N. Similarly, emissions factor of N2O were linearly increased with increased N fertilizer (0.15, 0.36 and 0.73%, for excreta, excreta + 75 kg N and excreta + 150 kg N). Therefore, the interaction between N fertilizer and excreta on N2O emissions in tropical pastures was additive.