Effects of grazing management and buffer strips on metal runoff from pastures fertilized with poultry litter

Authors: PILON, CRISTIANE - University Of Arkansas; Moore, Philip; Pote, Daniel; Martin, Jerry; DELAUNE, PAUL - Texas A&M Agricultural Experiment Station

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/2/2017
Publication Date: 3/17/2017
Citation: Pilon, C., Moore Jr, P.A., Pote, D.H., Martin, J.W., Delaune, P.B. 2017. Effects of grazing management and buffer strips on metal runoff from pastures fertilized with poultry litter. Journal of Environmental Quality. 46(2):402-410.

Interpretive Summary: High metal concentrations in runoff from pastures that receive poultry litter fertilization may be detrimental to aquatic systems. The addition of buffer strips are conservation practices used to reduce loads of nutrients and sediments in runoff water. The objective of this study was to assess the long-term impact of grazing management and buffer strips on metal runoff from pastures fertilized with poultry litter. Fifteen watersheds were constructed to determine the effect of the following treatments on metal runoff: (1) hayed, (2) continuously grazed, (3) rotationally grazed, (4) rotationally grazed with a buffer strip, and (5) rotationally grazed with a fenced riparian buffer strip watersheds. The plots were fertilized with poultry litter each year at a rate of 5.6 Mg ha-1. Fertilization was omitted in the buffer areas. Metal concentrations and loads were variable among the years regardless of the treatment. Aluminum (Al) and iron (Fe) concentrations were strongly and positively correlated with suspended solids, indicating soil erosion was the primary source. Soluble Al and Fe were not related to total Al and Fe; however, there was a strong positive correlation between soluble and total copper (Cu) concentrations. The majority of total Cu and zinc (Zn) were in the water-soluble form. Rotationally grazed with a fenced riparian buffer and hayed managements decreased concentrations of Al, Cu, Fe, potassium (K), manganese (Mn), and total organic carbon (TOC) in the runoff water. The combination of a fenced riparian buffer with a rotational grazing management or the conversion of the pasture to a hayfield appear to be two effective best management practices to decrease concentrations and loads of metals in runoff water from fields receiving poultry litter fertilization, thus reducing the negative environmental impact of poultry litter and maintaining high water quality.

Technical Abstract: Metal runoff from fields fertilized with poultry litter may pose a threat to aquatic systems. Buffer strips have been added to fields to reduce nutrients and solids runoff. However, scant information exists on the effects of buffer strips combined with grazing management strategies on metal runoff from pastures. The objective of this study was to assess the long-term impact of grazing management and buffer strips on metal runoff from pastures fertilized with poultry litter. Fifteen watersheds were constructed to determine the long-term effect of the following treatments on metal runoff: (1) hayed, (2) continuously grazed, (3) rotationally grazed, (4) rotationally grazed with a buffer strip, and (5) rotationally grazed with a fenced riparian buffer strip watersheds. The plots were fertilized with poultry litter each year at a rate of 5.6 Mg ha-1. Fertilization was omitted in the buffer areas. Metal concentrations and loads were variable among the years regardless of the treatment. Aluminum (Al) and iron (Fe) concentrations were strongly and positively correlated with suspended solids, indicating soil erosion was the primary source. Soluble Al and Fe were not related to total Al and Fe; however, there was a strong positive correlation between soluble and total copper (Cu) concentrations. The majority of total Cu and zinc (Zn) were in the water-soluble form. Rotationally grazed with a fenced riparian buffer and hayed managements decreased concentrations of Al, Cu, Fe, potassium (K), manganese (Mn), and total organic carbon (TOC) in the runoff water. The combination of a fenced riparian buffer with a rotational grazing management or the conversion of the pasture to a hayfield appear to be two effective best management practices to decrease concentrations and loads of metals in runoff water from fields receiving poultry litter fertilization, thus reducing the negative environmental impact of poultry litter and maintaining high water quality.