Abstract
Sewage sludge derived from municipal sewage treatment plants is an important source of macronutrients, micronutrients and organic matter. For this reason composting of sewage sludge, along with combustion and co-combustion, is a new management priority in Poland. In this study six composts of different origin and composition were evaluated in terms of their abundance in phosphorus, because it is an essential nutrient for all living organisms. Analyses were conducted on the samples at the initial and at the maturation phase of composting. The bioavailability of phosphorus was estimated on the basis of amounts of the nutrient in isolated fractions using the sequential extraction method. First of all quantitative changes of the total nutrient content and its amounts in separated fractions were dependent on the mixture composition. Irrespective of compost type, 34.5–75.0% of the total amounts of phosphorus were found in hardly available combinations (Fr. III), while available phosphorus forms (Fr. I) accounted for only 6.6–21.6%. As a result of composting together different organic wastes an increase was observed both in the total content and the amounts of this nutrient in separated fractions. This phenomenon was observed particularly in composts with smaller levels of sewage sludge (30–40%), characterised by rapid organic matter decomposition, which was indicated by higher bioavailable amounts of phosphorus. Under such conditions the content of P ranged between 3.68 and 7.4 g kg−1. In comparison to the labile pool of P obtained for matured composts C5 and C6 (65 and 75% of sewage sludge in their composition) amounting to 2.45–3.0 g kg−1 the above values were considerable. Bioavailable phosphorus contents potentially introduced to soil with composts doses calculated at 170 kg total N/ha/yr ranged from 69.8 to 80.2 kg for compost with the lowest share of sewage sludge and from 11.2 to 20.7 kg for compost with the highest share of sewage sludge.
Highlights
Phosphorus, together with nitrogen, potassium, sulphur and magnesium, is one of the macronutrients needed by all plants, so inputs of phosphorus are necessary to maintain profitable crop production
A number of microbiological and chemical processes take place in the course of composting, which can result amongst other things, in a loss of organic matter, Table 4
The results presented show that the interaction of composting time and mixture composition had a significant influence on the total P content
Summary
Phosphorus, together with nitrogen, potassium, sulphur and magnesium, is one of the macronutrients needed by all plants, so inputs of phosphorus are necessary to maintain profitable crop production. The majority of P nutrient is applied as inorganic fertiliser derived from minerals such as phosphate rock.[1] Literature data [2,3] suggest that current high-grade reserves of phosphorus rock will be depleted within 50–150 years. A considerable body of literature [1,5,6] supports the view that organic matter from compost or biowastes is a very important and valuable source of P. Application of such organic substances may increase P solubility and decrease its precipitation. Some positive mechanism might be involved such as improvement of soil pH, and complexation of soluble Al and Fe by organic molecules.[5]
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