Sewage Sludge Fertilisation Influence On Main Soil Chemical Features

Sludge from wastewater are containing particles of clay, organic matter from sewage and human waste, salts, detergents, heavy metals. Sewage sludge can be used as fertilising resource fresh, after anaerobic fermentation for biogas and dried on dehydration beds. Most commonly used as fertiliser is fermented sludge which is used as manure or compost. Dried sewage sludge can contain 20-60% dry matter, 25-40% organic matter, 5.1% total N, 0.5 to 4% P2O5, 0.5% K2O and 6.5% Ca. Sewage sludge is considered valuable phosphorus fertiliser, being applied in autumn before plowing for cereals, fodder crops, potatoes, in dose of 25-60 t/ha, corresponding to the addition of nitrogen. Sewage sludge must be applied carefully, knowing the content of heavy metals and pathogens. In this paper we follow the effect of sewage sludge on soil main chemical features. Sludge was applied to a culture of Medicago sativa in three levels: 15,20 and 40 t ha(-1). Arise of soil pH values was observed. Nitrogen content was higher only in variant fertilised with 15 t ha-1. The values of phosphorus content were ranged between 35.76 and 87.82 mg kg(-1). Compared to control variant, potassium content increase is not significant.