SLU news

Organic pig production on pasture – ammonia losses

Published: 23 February 2012

Nitrogen losses from pigs on pasture are not very well explored. Eva Salomon and her colleagues examined two different grazing systems to find out when, where and why losses occur.

- There are few studies of nitrogen losses from pigs on pasture. Therefore, we wanted to examine two different grazing systems to evaluate when and where ammonia losses occur and what causes ammonia losses, says Eva Salomon.

Pigs are clean animals and therefore they have toilets. In this study, the distribution of nitrogen from faeces and urine was10 to 100 times greater on the part of the pen where the pigs had their toilet, compared to the surface where the pigs grazed or rooted. The pig toilet in the hut system was near the hut in the direction of the feed slot. In the stable system the toilet was on the concrete slab and on nearby land.

In consequence of this were also the greatest ammonia losses from the toilet (0056-1843 grams NH3 per hectare and hour), compared with grazed or rooted land (0.001 to 0.332 grams NH3 per hectare and hour). At the same time the ammonia losses showed most variation from grazed or rooted land. This was because the pigs peed sporadically when they were on their way to graze or forage and occasionally this was caught up in the measurement.

In one of the pasture systems the pigs had access to huts and feed trough was placed in the pen. The second grazing system had pens connected to a stable. Closest to the entrance, there was a concrete slab. The pigs were fed inside the house where they also had a litter.

- We also measured ammonia losses from a group of pigs in the hut system during the whole fattening period. Total ammonia losses corresponded to 0.66 kg per pig, which is 14 per cent of the nitrogen present in faeces and urine, says Eva Salomon.

Most of the ammonia losses occurred during the latter part of the fattening period, when the pigs ate the most. During the first 6 weeks of the fattening period, ammonia losses are negligible, despite summer temperatures.

One way to reduce ammonia losses is to minimize point loads by spreading the manure more evenly. To succeed, development of portable and functional huts, forage equipment and fencing systems is needed.

Another way is to develop low cost technologies or materials, collecting faeces and urine where the toilet is.

Ammonia losses contribute to eutrophication and acidification of land and water, and indirectly to emission of the greenhouse gas nitrous oxide. In Sweden, 85 per cent of ammonia emissions come from agriculture and especially the handling of manure. A small amount of ammonia emissions (8 per cent) come from grazing animals, which are mainly cattle and horses. About 1 per cent of hogs are organic and have access to pasture during the summer.