ARS | Publication request: Vertical distribution of phosphorus in agricultural drainage ditch soils

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 25, 2007
Publication Date: November 1, 2007
Citation: Vaughan, R.E., Needelman, B.A., Kleinman, P.J., Allen, A.L. 2007. Vertical distribution of phosphorus in agricultural drainage ditch soils. Journal of Environmental Quality. 36:1895-1903.

Interpretive Summary: Land drainage for agricultural, construction, and public health purposes has been a prominent landscape feature in the United States and Europe for over four centuries. As drainage ditches typically intercept or border agricultural fields, they are a key link between farm land and surface waters. This study sought to evaluate processes affecting the nature of materials found in the bottom of drainage ditches to identify opportunities for improved management of ditches. A variety of features, many of them found in the subsurface, potentially affect the fate of phosphorus. The distribution of phosphorus was particularly affected by the accumulation of organic matter and removal of iron as part of repeated oxidation/reduction cycles. Findings of this study raise key concerns regarding the conventional ditch management practice of dredging and point to the need to consider a variety of factors in developing strategies for water quality protection.

Technical Abstract: Pedological processes such as gleization and organic matter accumulation may affect the vertical distribution of P within agricultural drainage ditch soils. The objective of this study was to assess the vertical distribution of P as a function of horizonation in ditch soils at the University of Maryland Eastern Shore Research Farm in Princess Anne, Maryland. Twenty-one profiles were sampled from 10 agricultural ditches ranging in length from 225 to 550 m. Horizon samples were analyzed for total P, water-extractable P, Mehlich-3 P, acid ammonium oxalate-extractable P, Fe, and Al, pH, and organic C (n = 126). Total P ranged from 27 to 4882 mg/kg, oxlalate P from 4 to 4631 mg kg/1, Mehlich-3 P from 2 to 401 mg/kg, and water-extractable P from 0 to 17 mg/kg. Soil forming processes that result in differences between horizons had a strong relationship with various P fractions and P sorption capacity. Fibric organic horizons at the ditch soil surface had the greatest mean oxalate P, F, and Al concentrations of any horizon class. Gleyed A horizons had mean oxalate Fe concentrations 2.6 times lower than did dark A horizons and were significantly lower in Total P and oxalate P. Variation in P due to organic matter accumulation and gleization provide critical insight into short- and long-term dynamics of P in ditch soils and should be accounted for when applying ditch management practices.