Ammonia volatilization from sows on grassland

According to regulations, sows with piglets on organic farms must graze on pastures. Volatilization of ammonia (NH3) from urine patches may represent a significant source of nitrogen (N) loss from these farms. Inputs of N are low on organic farms and losses may reduce crop production. This study examined spatial variations in NH3 volatilization using a movable dynamic chamber, and the pH and total ammoniacal nitrogen (TAN) content in the topsoil of pastures with grazing sows was measured during five periods between June 1998 and May 1999. Gross NH3 volatilization from the pastures was also measured with an atmospheric mass balance technique during seven periods from September 1997 until June 1999. The dynamic chamber study showed a high variation in NH3 volatilization because of the distribution of urine; losses were between 0 and 2.8 g NH3–N m−2 day−1. Volatilization was highest near the feeding area and the huts, where the sows tended to urinate. Ammonia volatilization rate was linearly related to the product of NH3 concentration in the boundary layer and wind speed. The NH3 in the boundary layer was in equilibrium with NH3 in soil solution. Gross NH3 volatilization was in the range 0.07–2.1 kg NH3–N ha−1 day−1 from a pasture with 24 sows ha−1. Ammonia volatilization was related to the amount of feed given to the sows, incident solar radiation and air temperature during measuring periods, and also to temperature, incident solar radiation and rain 1–2 days before measurements. Annual ammonia loss was 4.8 kg NH3–N sow−1.