Differential release of manure-borne bioactive P Forms to runoff and leachate under simulated rain

Authors: BLAUSTEIN, RYAN; DAO, THANH; Pachepsky, Yakov; SHELTON, DANIEL

Submitted to: Journal of Environmental Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/24/2017
Publication Date: 1/31/2017
Citation: Blaustein, R.A., Dao, T.H., Pachepsky, Y.A., Shelton, D.R. 2017. Differential release of manure-borne bioactive P Forms to runoff and leachate under simulated rain. Journal of Environmental Management. 192:309-318.

Interpretive Summary: An information deficit exists about the release of phosphorus from a manure layer free from the interference of the soil surface’s properties. Numerous turbulent interactions and exchanges occur between runoff water and the surface of an underlying soil that misrepresent the true size of manure phosphorus loss. Best management practices, numerical indices of susceptibility to losses of phosphorus also known as the phosphorus index, decision-aid tools, and computer models have been developed to predict phosphorus loss in runoff and leaching. These tools use manure soluble phosphorus content to predict susceptibility to losses for most agricultural soils and landscapes across the U.S. This study showed that runoff contained soluble phosphorus and organic phosphorus forms that can be as large a fraction as that of inorganic soluble phosphorus. Contrary to current prevalent views, rainfall intensities also altered the inorganic and organic phosphorus proportion in runoff and leachates. The detailed analysis for four identified bioactive phosphorus forms, in addition to water-soluble forms in runoff will help crop, soil, and nutrient managers and producers in their effort to optimize nutrient conservation practices to reduce runoff loss of excess phosphorus to the environment.

Technical Abstract: Limited information exist on the release of bioactive forms of P to runoff from a distinct manure layer, without the confounding effects of properties of the underlying soil in manure-amended fields to predict and model P partitioning and environmental behavior of the component P species. A study of the effects of three simulated rain intensities (30, 60, and 90 mm h-1) representative of mid-Atlantic region of the U.S. on the release and loading to runoff free from the effects of turbulence and mixing that occurs at the manure-soil interface, and the fraction that was to be carried to a presumed top layer of an underlying soil. The temporal distribution of manure-borne P concentration in runoff and leachate from an equivalent application of 60 Mg ha-1 of dairy manure (wet weight basis) was described by the log-normal flux probability density distribution. The predicted amplitudes of the TP distribution in runoff increased (0.125, 0.150, and 0.160) as rainfall intensity increased. The time of occurrence of concentrationmax also got shorter as rainfall intensified, and the distributions of TP in runoff were also less broad, with distributions’ width at half-concentrationmax (FWHM) decreasing from a width of 15.5, 8.4, to 5.7 min for the 30, 60, and 90 mm h-1 treatments, respectively. The mass balance, however, showed most of the P remained behind in the manure after the 1-h simulation. Runoff and rainwater infiltrating the manure pore space transferred less than 1% of the added P out of the manure layer, to presumably, the surface layer of an underlying soil. Runoff contained not only water-extractable (WEP) but also total exchangeable and enzyme-labile bioactive P (TBIOP), in contrast to the functional of the often-reported dissolved-reactive P (DRP) fraction. Rainfall intensities not only altered the form of the log-normal probability density distribution, as reflected in shifts in the characteristic parameters, but intensity also altered the bioactive P composition in runoff and leachate. Increased proportion of WEP in the runoff suggested preferential desorption and convection of inorganic forms under the 90 mm h-1 treatment, while TBIOP remained relatively constant. Detailed P forms and their distribution are thus critically needed to improve prediction of agricultural P transport and improved evaluation of risks of water quality impairment to nearby aquatic ecosystems.