Sewage sludge incinerator ash as a phosphorus source for corn and soybean

Abstract

Sewage sludge incinerator ash (SSA) contains significant amounts of phosphorus (P), a fundamental element required for basic cell metabolism and an essential plant macro-nutrient. However, SSA is often landfilled, and the P is lost from re-circulation in the food system. Our objectives were to understand the agronomic, soil chemical, and soil microbial impacts of SSA as a P amendment in an agronomic system – does SSA work as a P source, and what are its other effects? In a three-year corn and soybean field study in Rosemount, Minnesota, SSA was applied as well as triple superphosphate (TSP), biosolids, and struvite for comparison. Each P source was applied at 20, 40, 60, and 80 kg P ha-1 with a zero-P control included for each P source. Plant, soil, soil solution, and microbial samples from bulk soil were taken throughout the season to monitor plant yield, P uptake, soil P concentrations, the loading and uptake of plant micronutrients and trace elements of concern, and microbial metagenomic responses.The ash provided P for plant uptake and appears to be a slow-release form of P. Corn yields were high for all treatments across all years. In 2017, yields increased with increasing application rates of TSP only, while in 2018 corn yields did not response to any P source or rate. In 2019, corn yields increased with increasing P application of all P sources equally. Yields of soybean, which were planted without additional fertilization in that year, increased with increasing P application rates (applied the year before) equally across all P sources as well. Concentrations of available P and soil solution P in the top 15 cm of soil increased with the application of all P sources, though at a lesser response rate in SSA-amended plots. Soil concentrations of Cu and Zn increased with the application of SSA and biosolids, but only Zn concentrations increased in plant biomass. There were no biologically significant increases in soil or plant biomass of any other elements of concern. Additionally, while microbial communities shifted with crop and year, there were no significant differences in microbial community diversity or abundance based on P source or P application rate. Ultimately, the results from this study validated SSA land application as a safe and effective method of recycling an invaluable resource and demonstrated a local opportunity to reduce the impact of human life on our natural environment.