Methane Flux Measurements over a Rotational Grazed Pasture in Northern Kentucky

Minimizing excessive losses of protein and reducing nitrogen wasting bacteria in ruminants has long been noted as the main determinants of methane (CH4) produced by ruminants. Enteric fermentation from ruminating animals is the second largest global source of CH4 thus has received a great deal of attention in recent decades. These concerns highlight the importance of accurate CH4 quantification for determining the CH4 source or sink status managed with intensively rotational grazed pasture. We measured CH4 flux over a small paddock rotationally grazed with 40-70 goats managed in a rotational grazing system. We used the eddy covariance (EC) technique, at Kentucky State University (380 6’56.42 N, 840 53’ 22.81W). To investigate the grazing pattern of the animals relative to the tower location and to properly attribute the contribution of the goats to the measured flux, the position of 12 goats were tracked with GPS recorder both in the upwind and downwind areas (footprint). Diurnal CH4 analysis indicate much of the flux occurring during the night (5.9 μmol m-2 s-1), nearly 1.5x of the day time average (3.7 μmol m-2 s-1). Consistently, the cumulative CH4 flux was the highest (9.6 μmol m2 s-1) when the animals were grazed in the upwind compared to downwind (3.9 μmol m-2) (positive sign indicate the pasture was CH4 source). The average of CH4 flux from the early summer short grazing period (June to July) was relatively lower than the early grazing season (August 27 to September). Averaged over a short (May 5 - June2) and an extended mid-summer (July 15-Aug 26) non-grazing periods, the pasture was a net CH4 sink (-0.01 μmol m-2) and neutral (0.01 μmol m-2), respectively. This study underscores the importance of livestock methane emission contribution to the total greenhouse gas budget of intensely managed pasture. The contrasting results might also provide information to inform management strategies towards i) increasing the pasture’s diet quality for animals and ii) improving the digestibility and thereby reducing the nitrogen wasting bacteria. Both have shown to ameliorate CH4 emissions from ruminants