氮素是植物必要的营养元素之一，其主要来源有：生物固氮作用、降雨和灌溉水以及人工施肥。
Nitrogen for plant nutrition is mainly obtained from three sources: nitrogen-fixing plant, rain water and manure.
氮素是植物必要的营养元素之一，其主要来源有：生物固氮作用、降雨和灌溉水以及人工施肥。
Nitrogen for plant nutrition is mainly obtained from three sources: nitrogen-fixing plant, rain water and manure.
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