Biosolids processing effect on sulfur plant availability

Understanding the S nutritive value of biosolids produced by various processing methods is important for growers who apply biosolids to crop production fields. Our project goals were to determine how processing method and biosolids' properties influence S availability and S fertilizer value. Fourteen biosolids materials were selected for the trial, including those produced with aerobic digestion (n = 2), anaerobic digestion (n = 5), dual digestion (n = 1), composting (n = 2), lagoon storage (n = 2), sawdust blending (n = 1), and alkaline stabilization (n = 1). Biosolids were air-dried, ground, and added to a Walla Walla silt loam soil at a rate of 100 mg S kg(-1) soil. The treated soils were incubated at 25 celcius and extracted for SO4-S on Days 1, 13, 29, 44, and 83. Mean plant available S was greatest for the alkaline stabilized biosolids (52%), followed by anaerobically digested biosolids (40%), sawdust blended biosolids (37%), lagoon slurry (36%), dual digestion biosolids (31%), aerobically digested biosolids (15%), and composted biosolids (4%). Biosolids pH, organic C/total S, total Ca, total S, and SO4-S concentrations were well correlated to S release rate, plant available S, or both. Sulfur mineralization of organic S compounds is known to be influenced by organic C/total S, whereas Ca and pH effects may be related to gypsum (CaSO4) dissolution and oxidation of hydrogen sulfide compounds. The correlations discussed here may need to be further investigated and verified on additional soil types and under field conditions prior to grower adoption.

Automated summary

Understanding the sulfur (S) nutritive value of biosolids produced by different methods is essential for growers using biosolids in agriculture. The study found that alkaline stabilized biosolids had the highest plant available S content, and properties like pH, organic C/total S, total Ca, total S, and SO4-S concentrations were correlated with S release rate and plant available S. Further investigation is needed to verify these correlations in different soil types and field conditions.