Nitrogen mineralization of sewage sludges in soil

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Abstract
The returning of sewage sludges or animal manure into crop fields is considered to be one of the most effective methods in reducing the use of industrially produced fertilizer, which consumes high cost oil energy, as well as utilizing the mineral nutrients in the wastes for crop production. If this route of mineral cycling is developed, careful examination is needed to protect crop lands and human environment from any possible pollution problem. Sometimes sewage contains a high amount of heavy metals (2) and usually contains a large amount of nitrogenous compounds, which are mostly microbial proteins and easily mineralized into ammonia or nitrate. The heavy metals and inorganic nitrogen (mainly nitrate) may cause a pollution problem to our environment, if their concentration in the soil is high. High nitrate content of vegetables is sometimes a result of a high concentration of nitrate in soil (7). The run-off of inorganic nitrogen from agricultural lands is considered to be one of the causes of the high nitrate content in the water of rivers and lakes (1).

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