Vertical distribution of phosphorus in agricultural drainage ditch soils

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 (P_ox, Fe _ox, Al_ox); pH; and organic C (n = 126), Total P ranged from 27 to 4882 mg kg^-1, P_ox from 4 to 4631 mg kg ^-1, Mehlich-3 P from 2 to 401 mg kg^-1, and water-extractable P from. 0 to 17 mg kg^-1. 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 P_ox, Fe_ox, and Al_ox concentrations of any horizon class. Gleyed A horizons had a mean Fe_ox concentrations 2.6 times lower than dark. A horizons and were significantly lower in total P and P_ox. 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.