SURFACE AND SUBSURFACE PHOSPHORUS LOSSES FROM FERTILIZED PASTURE SYSTEMS IN OHIO

Authors: Owens, Lloyd; Shipitalo, Martin

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/2/2006
Publication Date: 7/5/2006
Citation: Owens, L.B., Shipitalo, M.J. 2006. Surface and subsurface phosphorus losses from fertilized pasture systems in Ohio. Journal of Environmental Quality. 35:1101-1109.

Interpretive Summary: Phosphorus is an essential nutrient for all plant growth, but it is an environmental problem when excessive amounts enter surface waters. Agricultural land use is among several possible sources of P to surface waters. This study assessed the P concentrations and transport in storm runoff events from medium and high fertility pasture systems. Larger storms carried more P than smaller ones, but there was no correlation between P concentration and size of the runoff event. The highest P concentrations in surface runoff were in events that occurred soon after P fertilizer application. Much more P was lost from the pasture systems in surface runoff than via subsurface flow. Average seasonal P concentrations in subsurface water were less than 0.05 ppm. This indicated that applying P fertilizer to pastures in response to soil tests should keep Tot-P concentrations in subsurface flow at environmentally acceptable levels. Phosphorus losses varied more with season than with pasture system. Management to reduce runoff and avoidance of P fertilizer application when runoff producing rainfall is anticipated in the next few days will help reduce the surface losses of P. This information will be useful to other scientists, producers and land use advisers.

Technical Abstract: Phosphorus is an essential plant nutrient and critical to agricultural production, but it is also a problem when excessive amounts enter surface waters. Summer rotational grazing and winter feed beef pasture systems at two fertility levels (56 and 28 kg available P/ha) were studied to evaluate the P losses from these systems via surface runoff and subsurface flow using eight small (0.3 to 1.1 ha), instrumented watersheds and spring developments. Runoff events from a 14-yr period (1974-1988) were evaluated to determine the relationships between event size in mm, total-P (Tot-P) concentration, and Tot-P transport. Most of the P transported was via surface runoff. There were strong correlations (r2 0.45 to 0.66) between Tot-P transport and event size for all watersheds, but no significant (P= 0.05) correlations between Tot-P concentration and event size. Flow-weighted average Tot-P concentrations from the pasture watersheds for the 14-year period ranged from 0.64 to 1.85 mg L-1 with a few individual event concentrations as high as 85.7 mg L-1. The highest concentrations were in events that occurred soon after P fertilizer application. Average seasonal flow-weighted Tot-P concentrations for subsurface flow were <0.05 mg L-1. Applying P fertilizer to pastures in response to soil tests should keep Tot-P concentrations in subsurface flow at environmentally acceptable levels. Management to reduce runoff and avoidance of P fertilizer application when runoff producing rainfall is anticipated in the next few days will help reduce the surface losses of P.