Abstract
Land application of biosolids (SS) can cause a buildup of phosphorus (P) in the top soil. The changes in the soil P characteristics may be assessed by the sorption isotherm and the sequential fractionation techniques. Samples of Haplorthox were collected from a field experiment where maize was cultivated for two years, after two applications of SS originated from two cities of São Paulo State, Brazil. SS applications added a total of 125, 250, 500, 1000 and 2000 kg ha−1of P in the area. To perform the sorption isotherms and obtain P maximum sorption capacity (Qmax) and the binding energy, soil samples were submitted to increasing P concentration solutions until equilibrium was reached. Sequential fractionation was done by a sequential extraction with CaCl2, NaHCO3, NaOH, HCl, and HNO3+ HClO4(residual). Addition of biosolids from both cities to the soil decreasedQmaxand the binding energy obtained by the Langmuir equation. SS additions changed the P fractions distribution in the soil by increasing the labile fractions (P-CaCl2and P-NaHCO3) and the moderately labile fraction (P-NaOH) by 11.2% and 20.3%, respectively, in detriment of the most resistant P fraction.
Highlights
A sustainable option to dispose biosolids (SS) originated from sewage treatment plants is the use as soil conditioner or as a source of nutrients to plants
It is supposed that frequent SS addition can increase the soil organic matter content which has a positive correlation with the capacity of soil in retaining P [5]
Organic matter (OM) was determined by a colorimetric procedure, after digestion of samples with sodium dichromate solution in sulfuric acid and comparing the readings with a standard curve prepared with soil samples previously analyzed by Walkley-Black’s method [9]
Summary
A sustainable option to dispose biosolids (SS) originated from sewage treatment plants is the use as soil conditioner or as a source of nutrients to plants. Among the useful parameters to monitor the increase in soil P availability is the P sorption capacity and P distribution among the main soil fractions. The application of organic residues to soils might implicate in change in soil P sorption capacity. According to Reddy et al [3], application of organic wastes increases soluble P and decreases the P sorption capacity of the soil, and these parameters were directly related to the loading rates of animal wastes. Some organic acids released during residue decomposition might compete with P for the same sorption sites in the soil solid phase, decreasing the element immobilization or forming stable complexes with Fe and Al and blocking P retention by them [4]. It is supposed that frequent SS addition can increase the soil organic matter content which has a positive correlation with the capacity of soil in retaining P [5]
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