Changes in soil test phosphorus and soil cations following application of sewage sludge ash and other recycled phosphorus fertilizers
Ma, P., A. Rendahl, D. Kaiser and C. Rosen . 2025.
Abstract
Phosphorus (P) is essential to healthy plant development and is regularly applied in
agronomic settings to ensure maximum crop yields. Sewage sludge incinerator ash
(SSA) contains significant amounts of P and was investigated as a recycled P fertil-
izer in a 3-year field study. Untreated SSA was applied at a range of agronomically
appropriate rates based on water- and citrate-soluble phosphate (WCSP) concentra-
tions in a corn and soybean field study in Minnesota (Waukegan silt-loam, pH 6.8)
to determine the soil chemical effects of SSA amendment individually and compared
with triple superphosphate (TSP), biosolids, and struvite. Concentrations of Olsen-
P and soil solution P ion fluxes from in-situ plant root simulator probes increased
with increasing rates of SSA and were significantly greater than control plots. Com-
pared to the other P sources, SSA amendment increased soil test P at 50% - 70% the
increase observed with TSP amendment, while total P concentrations increased at
1.7 - 32.5 times the rate of increase with other P sources. This was due to the lower
WCSP concentrations in SSA and the experimental choice to apply based on WCSP.
Soil-extractable concentrations and ion fluxes of copper (Cu) and zinc and total soil
concentrations of Cu increased with SSA and biosolids application, indicating poten-
tial as a comprehensive nutrient source. Total concentrations of concerning elements
including arsenic, cadmium, chromium, and lead did not increase above detection
limits. Total mercury concentrations were statistically higher with SSA application
compared with the control and other P sources, though the analytical sensitivity
was significantly higher, and the increase was biologically marginal (an increase
of 0.06 μkg-1 P applied as SSA). Overall, soil chemical responses indicated that
SSA increased concentrations of soil test P and some plant nutrients with minimal
increases in concentrations of elements of concern.
