A broiler chicken produces an average 115g excrements a day; this amounts to 2 million tons a year in Germany alone. In terms of plant nutrients this is equivalent to 33 million kg nitrogen (N) and 7 million kg phosphorus (P). The environmetal effects of these nutrients and their interaction with different production systems has been investigated by scientists of the Institute of Plant Nutrition and Soil Science of the Federal Agricultural Research Centre (FAL) in Braunschweig, Germany.
Intensive indoor broiler production
Photograph: Martina Wolf-Reuter
Organic free range broiler production wth mobile housing
Photograph: Martina Wolf-Reuter
A nationwide study compared intensive indoor, free range and organic broiler production systems. In the intensive indoor system with 22-24 animals per square metre, i.e. altogether 20,000-40,000 animals in one building (picture 1), the birds achieve their final weight of 1.8 kg after roughly 6 weeks and during that time they have produced "only" about 5 kg excrements per broiler. However these accumulated high amounts of excrements cannot be disposed of easily and only by following the approved codes of "good agrcultural practice", which states the amount per acre according to be applied according to the approved N and P needs of plants.
The free range chicken, shares a square meter with 13 others, in flocks of about 6,000-15,000 birds and an average stocking rate of about 1 m2 per bird in the free range. This makes their life not only more varied but also a bit longer. In spite of the same final fattening weight of 1.8 kg, their life is extended by two weeks, which therefore leaves more droppings. An additional problem: During the study the birds mostly stayed near their building, so hardly more than 30 % of the actual exercise area was used with the consequence, that it received a far higher enrichment with N and P, to the extent that it was a potential pollution risk to the ground- and surface waters.
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