Nitrate dynamics in biosolids-treated soils. I. Influence of biosolids type and soil type

The main types of urban wastewater biosolids currently recycled as agricultural fertilizers and soil improvers were incubated with two contrasting soils as a first stage in developing a model of NO3-N formation in biosolids-treated soil. The different types of biosolids were qualitatively separated into four distinct categories according to whether they showed high NO−3 production potential (Category 1), intermediate to low accumulation potential (Category 2), initial immobilization of native soil mineral N followed by a phase of very limited NO−3 production (Category 3) or high resistance to mineralization and NO−3 formation (Category 4). Soil physico-chemical properties modulated the patterns of NO−3 accumulation from the biosolids. However, the dominant factors controlling the rate and extent of NO−3 formation in amended soil were biosolids type, soil temperature and time from soil incorporation.