Journal article
Phosphorus availability of sewage sludges and ashes in soils of contrasting pH
Background: Little is known about the relationship between plant availability of P in different sludges and their derived ashes, its development over time and its interaction with soil pH. Aim: This study addresses this knowledge gap, by investigating the P availability and fractions of six sludges produced under different conditions and the incineration ashes derived from five of these, plus the effect of time (84 days) and soil pH on P availability.
Methods: These materials were applied to two similar soils with contrasting pH (5.8 and 7.8), based on the assumption that lower pH would favor plant availability of P from these sources. Triple super phosphate and a control (no P addition) were included as references. Results: The relative P fertilizer availability (RFA) in soil of both sludges (18–77%) and ashes (0.1–25%), measured as water extractable P, was found to be highly dependent on their origin.
While the P availability of sludges was strongly affected by soil pH, ash P availability showed either no or little soil pH effect, in contrast to our expectations. For the sludges, RFA was negatively correlated to the ratio (Fe+Al)/P in both pH soils and positively correlated to sludge water extractable P in the higher pH soil.
For the ashes, the ratio Fe+Al to P and the pH reaction of ashes in water were strongly negatively correlated with RFA in the lower pH soil. Ca/P ratios did not predict RFA in either sludges or ashes. Nevertheless, we ascribe the comparably higher average RFA in sludges of 58% found in the low pH soil compared to 25% in the alkaline soil to the greater solubility of Ca-P species under lower pH.
For ashes, the availability increased over time, while rather stable for sludges. Conclusion: In conclusion, the P availability of both sludges and ashes was highly dependent on their origin, and for sludges highly dependent on soil pH.
Language: | English |
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Year: | 2020 |
Pages: | 682-694 |
ISSN: | 15222624 and 14368730 |
Types: | Journal article |
DOI: | 10.1002/jpln.201900323 |
ORCIDs: | 0000-0003-2997-4434 , 0000-0003-0358-434X , 0000-0002-1446-2084 , 0000-0001-5867-0910 and Scheutz, Charlotte |