Greenhouse gas emissions from naturally ventilated freestall dairy barns

Abstract

Greenhouse gas (GHG) emissions from two naturally-ventilated dairy freestall barns measured for a total of 21 d, one week each in May, July, and September 2009, are presented in this article. The holding capacity of Barn 1 (B1) was 400 Holstein cows, while that for Barn 2 (B2) was 850 cows. Air samples were taken from inlets and outlets of the barns via a custom made multiplexer gas sampling system for measurement of gas concentrations using a photoacoustic infrared multigas analyzer. Barn ventilation rates were based on air velocity measured with arrays of 3-D ultrasonic anemometers at inlets and outlets. Gas concentrations (10 min means) in the barns ranged from: 443–789 ppm for CO2, 0.0–39.4 ppm for CH4, and 0.25–0.39 ppm for N2O; with mean concentrations ranging from 6 to 20%, 0 to 4%, and 26 to 180% above the average background concentrations for CO2, N2O, and CH4, respectively. The correlations between CO2 and CH4 enhanced concentrations were relatively stronger (R of 0.67–0.74) than between CO2 and N2O enhanced concentrations (R of 0.10–0.20). Environmental conditions did not significantly (p = 0.46) impact the enhanced concentrations of N2O in the barns. All three parameters (T, RH, and v) had significant (p < 0.01) influences on CO2 enhanced concentrations; while only T (p < 0.01) and v (p < 0.01) had significant influences on CH4 enhanced concentrations. Enhanced concentrations of CO2 and CH4 correlated negatively with all three parameters. The influence of the temperature-humidity index (THI) on CO2 enhanced concentrations was higher than that of v; while the effect v had on CH4 enhanced concentrations was slightly higher than that of the temperature-humidity index. The average emissions, based on hourly means, ranged from 5.3 to 10.7 kg d−1 AU−1 for CO2; 0.3 to 2.5 g d−1 AU−1 for N2O; and between 67 and 252 g d−1 AU−1 for CH4. Nitrous oxide emissions from the smaller barn, B1 (0.4–2.5 g d−1 AU−1), were significantly higher than from the larger barn, B2 (0.3–0.5 g d−1 AU−1) most probably because 50% of B1 was open (no stalls) loose dirt floor.