Sheep Excreta as Source of Nitrous Oxide in Ryegrass Pasture in Southern Brazil

Michely Tomazi,Joice Mari Assmann,Paulo Cesar De Faccio Carvalho,Emanuelle Cavazini Magiero,Tatiane Bagatini,Cimélio Bayer,Jeferson Dieckow

doi:10.1590/01000683rbcs20140497

Abstract

ABSTRACT Livestock urine and dung are important components of the N cycle in pastures, but little information on its effect on soil nitrous oxide (N2O) emissions is available. We conducted a short-term (39-day) trial to quantify the direct N2O-N emissions from sheep excreta on an experimental area of ryegrass pasture growing on a Typic Paleudult in southern Brazil. Four rates of urine-N (161, 242, 323, and 403 kg ha-1 N) and one of dung-N (13 kg ha-1 N) were applied, as well as a control plot receiving no excreta. The N2O-N emission factor (EF = % of added N released as N2O-N) for urine and dung was calculated, taking into account the N2O fluxes in the field, over a period of 39 days. The EF value of the urine and dung was used to estimate the emissions of N2O-N over a 90-day period of pasture in the winter under two grazing intensities (2.5 or 5.0 times the herbage intake potential of grazing lambs). The soil N2O-N fluxes ranged from 4 to 353 µg m-2h-1. The highest N2O-N fluxes occurred 16 days after application of urine and dung, when the highest soil nitrate content was also recorded and the water-filled pore space exceeded 60 %. The mean EF for urine was 0.25 % of applied N, much higher than that for dung (0.06 %). We found that N2O-N emissions for the 90-day winter pasture period were 0.54 kg ha-1 for low grazing intensity and 0.62 kg ha-1 for moderate grazing intensity. Comparison of the two forms of excreta show that urine was the main contributor to N2O-N emissions (mean of 36 %), whereas dung was responsible for less than 0.1 % of total soil N2O-N emissions.

Highlights

Agriculture and land use change in Brazil are responsible for 91 % of the country’s nitrous oxide (N2O) emissions, and deposition of livestock excreta on pasture soils is responsible for 40 % (Brasil, 2010)
We previously found that lambs (30 kg live weight) expelled an average of 75 mL urine per urination (10.05 g L-1 of N; 6.8 g L-1 of organic carbon - OC), on an area of 31 cm2 (0.0031 m2); and 2.1 g dry matter (DM) of dung per defecation (9 g kg-1 of N; 414.8 g kg-1 of OC), on an area of 15.5 cm2 (0.00155 m2)
The N2O-N fluxes from the control soil ranged from 4 to 53 μg m-2 h-1 throughout the trial period (Figure 2) and no change occurred in this flux after dung application, with an almost negligible effect from the excreta

Summary

Introduction

Agriculture and land use change in Brazil are responsible for 91 % of the country’s nitrous oxide (N2O) emissions, and deposition of livestock excreta on pasture soils is responsible for 40 % (Brasil, 2010). The two main microbial processes of N2O production after urine and dung are deposited on the soil are nitrification, in which ammonia is oxidized to nitrite and to nitrate, and denitrification, in which nitrate is reduced to N2O or N2 (Carter, 2007; Saggar et al, 2008). Both processes probably occur simultaneously due to the diversity of the soil environment (Carter, 2007)

Methods

Results

Conclusion