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在许多欧洲国家,畜牧业占到其农业生产总值的一半以上(表1)。在某些地区,畜牧业在地域上高度集中,以致从环境上讲,产生的粪便超过了农田安全施用的程度。当粪肥(还有化肥)的使用超过了作物的需要时,多余的养分,如氮就会流入公共水域。第二次世界大战以前,农民靠自产的作物饲养牲畜,限制了牲畜头数,因此污染的风险小得多。但在60年代,随着封闭式畜牧生产技术的推广,畜牧业经营规模扩大并更
Livestock has accounted for more than half of its agricultural output in many European countries (Table 1). In some areas, livestock husbandry is highly geographically concentrated, so that the excrement produced is more environmentally safe than farmland. When manure (and fertilizer) is used more than needed for crops, excess nutrients, such as nitrogen, flow into public waters. Prior to the Second World War, farmers raised their own livestock crops, limiting the number of livestock, so the risk of pollution is much smaller. However, in the 1960s, with the promotion of closed livestock production technology, the scale of livestock husbandry expanded and more