Polydentate ligand-like substances in manure impacting soil sorption and transport of phytate phosphorus

Authors: Dao, Thanh

Submitted to: Journal of Waste Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/27/2017
Publication Date: 7/15/2017
Citation: Dao, T.H. 2017. Polydentate ligand-like substances in manure impacting soil sorption and transport of phytate phosphorus. Journal of Waste Management. 228:Article No. 279. https://doi.org/10.1007/s11270-017-3453-y.
DOI: https://doi.org/10.1007/s11270-017-3453-y

Interpretive Summary: In regions with high concentration of confined animal production operations, repeated manure application over the years has resulted in large accumulations of total phosphorus in amended soils. Land application of phosphorus-enriched manure has often been linked to spikes of dissolved phosphorus in runoff because manure-amended soils often have high labile phosphorus levels. Animal manure also contains labile organic phosphorus forms because of the grain-rich diets used in the finishing stage of market-ready livestock, or the growth stage-based feeding systems used in intensive poultry production operations. ARS scientists have found large amounts of enzyme-labile phosphorus forms in poultry litter and in litter-amended soils under conventional and organic farming management. Feces of ruminant livestock and soils receiving long-term applications of cattle manure also have elevated contents of organic labile phosphorus forms. As phosphorus build up in these soils, corrective measures implemented in watersheds at risk during the past decade have not shown the expected improvement in the water quality of affected streams and reservoirs. A study of potential changes in the mechanism by which phosphorus is retained in the soil, in particular, soil-amended with liquid manure was conducted to investigate their linkage to the persistence of the continual release of labile phosphorus. The impact and mechanisms by which complex decomposition products released during the breakdown of the organic matrix of dairy manure on the behavior and transport of agricultural phosphorus are largely unanswered questions. The study results showed that the liquid portion of dairy slurry/manure contains organic substances that behave in similar ways to man-made chemical promoters of solubility of phosphorus in water. These manure compounds were found to suppress the breakdown, and maintained soluble phosphorus in solution and enhance the transport of the organic phosphorus in soil, moving with the diluted manure liquid. Therefore, the release of soluble manure components to percolating water and runoff can be critical in assessing the transport and dispersion of organic phosphorus forms in soil. The phenomenon appears to hold the key to our improved understanding of the biochemical basis of legacy phosphorus in field soils and watersheds undergoing remediation for past excessive phosphorus loadings.

Technical Abstract: The impact and mechanisms by which complex decomposition products released during the breakdown of the organic matrix of land-applied animal manure on the behavior and transport of agricultural phosphorus (P) are largely undefined. A laboratory study was conducted to determine effects of a dairy manure liquid isolate on the sorption and transport of phytate (myo-Inositol hexa-kis-dihydrogenphosphate), an abundant enzyme-labile P forms in animal manure. Sorption isotherms' characteristics for phytate-P sorption on Christiana silt loam (Aquic Happluduts), Mattapex loam (Aquic Hapludults), and Unicorn sandy loam (Typic Hapludults) were determined in the P concentration range of 0.01-7.5 mmol L-1. The breakthrough of phytate-P (1.5 mmol L-1) was determined in short columns (ID= 74 mm; L=45 mm) of the Mattapex loam, where the effluent was collected periodically (2-h) and assayed for inorganic and enzyme-labile P. The isolate of the dairy manure liquid-phase was obtained following a 7-d incubation of reconstituted dairy cow manure (1.6:1, feces-to-urine) following centrifugation at 16,000 x g. The dairy manure liquid isolate, at dilutions of 19:1 to 1:1 water-to-manure liquid, reduced the sorption of phytate-P, with reduction in loge K averaging 30%. Whether the influent contained rain water or the manure liquid isolate at a water-to-isolate ratio of 19:1, significantly impacted the fate and pattern of the P breakthrough curves. Only inorganic phosphate-P was eluted in a two-stage process until reaching 100% of the P input concentration, after 16 pore volumes. Both inorganic P and enzyme-labile P appeared in the effluent when, either a solution of EDTA or one containing 5% of manure liquid isolate was used. Polydentate-like substances appeared to have reduced (i) the soils' affinity for phytate, and (ii) the hydrolysis rate in the soil and phytate eluted through the soil column. Therefore, components of the organic manure matrix, and their release to percolating and runoff water can play critical roles in controlling the transport and dispersion of organic P forms in soil. The process may hold the key to our understanding of the biogeochemical bases of the lag time in improvement of water quality in impaired watersheds undergoing remediation from past mismanagement.