Polydentate Ligand-Like Substances in Manure Impacting Soil Sorption and Transport of Phytate Phosphorus
2017
Dao, Thanh H.
The mechanisms by which complex products released from the organic matrix of cattle manure impact phosphorus (P) behavior and transport are largely undefined. Effects of a dairy slurry isolate on sorption characteristics of three benchmark soils and the breakthrough of phytate-P were determined in short soil columns of Mattapex loam (fine-silty, mixed, active, mesic Aquic Hapludults) under saturated flow conditions. The manure liquid isolate was obtained after a 7-day incubation of reconstituted dairy manure (1.6:1, feces-to-urine) at 37 °C and centrifugation at 16,000×g. The liquid isolate, at dilutions of 20:1 to 4:1 water-to-isolate, decreased soil sorption of phytate-P, with reduction in logₑ K averaging 30%. Whether the influent contained artificial rainwater or the manure isolate at a water-to-isolate ratio of 20:1, P retention and breakthrough curves were differentially impacted. Only inorganic phosphate-P was eluted in a multiple-stage process, and breakthrough occurred after 16 pore volumes of rainwater. Both inorganic- and enzyme-labile P (TBIOP) appeared in the effluent when either a dilute solution of 0.05 M EDTA (ethylenediamine-N, N, N′, N′-tetraacetate) or one containing 5% of manure liquid isolate was used as influent. The polydentate ligand-like substances reduced (i) the soil’s affinity for phytate and (ii) the hydrolysis rate in soil, allowing phytate to be eluted. Therefore, dissolved components of the manure matrix played critical roles in controlling transport and dispersion of phytate-derived P forms in soil and may hold the key to the understanding of biogeochemical bases of persistent effects of legacy P in agricultural watersheds.
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