Soil Use and Management (1999) 15, 27^33 Emission of NH 3 and N 2 O after spreading of pig slurry by broadcasting or band spreading M. Ferm, Ð.Kasimir-Klemedtsson, P.Weslien & L. Klemedtsson Abstract: The recommended method of reducing the emission of NH 3 while spreading manure is to plough or harrow the manure into the soil.This in turn increases the possibility of N 2 O emission. At two sites in southern Sweden emissions of NH 3 and N 2 O were measured after spreading pig slurry by broadcasting and band spread- ing.The band spreading technique can be used in growing crops i.e. when nitrogen is most needed, and it is thought that the NH 3 emission is smaller with this technique compared to broadcasting.The average NH 3 loss was 50% of applied NH  4 during warm=dry conditions and 10% during cold=wet conditions.The N 2 O emission was always less than 1% of applied NH  4 .When the NH 3 emission decreased, the direct N 2 O emission increased. However, when taking into account the indirect N 2 O emission due to deposition of NH 3 outside the field, the spreading techniques all produced similar total N 2 O emissions.The ammonia emission was not much lower for the band spreading technique compared to broadcasting, when compared on seven occasions. Keywords: Pig slurry, band placement, broadcasting, emission, ammonia, nitrous oxide, soil INTRODUCTION M eat production is very inefficient, with respect to nitrogen use, and most of the nitrogen in fodder is transformed to urine or manure. This is spread on agricul- tural land to fertilize crops. However, large amounts of ammonia (NH 3 ) are emitted during and after spreading of slurry. Nitrogen is also lost through nitrate leaching and nitrous oxide (N 2 O) emission. Nitrous oxide plays a role both in the radiative balance of the earth (Houghton et al., 1990) and in destruction of the stratospheric ozone molecules (Crutzen, 1976). In contrast to N 2 O, NH 3 has a more direct impact on the environment at the earth's surface, causing acidification and decreasing biodiversity (Ferm, 1998). A large fraction of the emitted NH 3 is deposited close to the source while the remainder reacts with acidic gases forming fine particles that are transported over long distances. Due to the different environmental effects of N 2 O and NH 3 , it is difficult to compare the environmental impact of the emis- sions, but both have to be mitigated. If the slurry is covered with moist soil during spreading, NH 3 emission decreases, and thus ploughing or harrowing the manure into the soil is recommended.This increases the probability of `hot spots' for N 2 O production. In order to reduce nitrate leaching it is also better to spread manure during the crop growing stage, which has the disadvantage that leaves may be damaged. New slurry spreading methods, aimed at decreasing the NH 3 emissions have been developed. Band spreading has an advantage in that it reduces the NH 3 loss and does not deposit slurry on the vegetation. The objectives of the research were to compare the effects of two methods of spreading pig slurry on emission of NH 3 (8 sites) and of N 2 O (at 2 of the 8 sites). SITES AND METHODS Site description The farms are situated in the south of Sweden (Table 1). NH 3 losses were measured at all the sites. The first experiment in which both N 2 O and NH 3 losses were measured (starting 18 May 1993) was performed at Sandby and the second (starting 16 May 1994) at Skivarp. The weather was sunny and dry at Sandby, but wet at Skivarp (Table 2). Pig slurry was spread by two techniques (N-amounts presented in Table 4). In the band spreading technique the slurry was pumped through 4cm thick tubing that trailed behind the tank. The slurry strips were c. 8 cm wide and 30 cm apart.The same machinery was used for broadcasting, but the slurry was pumped onto plates that spread the slurry evenly on the soil. On two occa- sions the plots were harrowed immediately after spreading. Measuring of NH 3 emissions The horizontal flux technique. This is a mass balance technique where all the NH 3 that enters or leaves the field horizontally is measured using low-cost passive samplers. Four masts with samplers at different heights are placed around the plot. Two samplers are connected in series where only the ones facing the wind receive NH 3 . The flux from the field and from the surroundings are therefore measured separ- ately. The amounts are then integrated up to a height at which the amount of NH 3 arising from the plot is negligible (Ferm, 1986; Schjoerring et al., 1992).The advantage with the technique is that the NH 3 uptake by the crop is taken into account. It can, however, be difficult to measure small emis- sions i.e. when the outgoing flux is only slightly larger than the incoming. The chamber technique. The NH 3 emission from soil (E) can be parameterized using three parameters, according to Swedish Enviromental Research Institute, P.O. Box 470 86, SE-402 58 Gothenburg, Sweden. Fax:  46 31 48 21 80 e-mail: Martin.Ferm@ivl.se M. Ferm et al. 27