Phosphorus Leaching in Manure‐Amended Atlantic Coastal Plain Soils

Abstract

Targeting the sources of phosphorus (P) and transport pathways of drainage from agricultural land will assist in the reduction of P loading to surface waters. Our research investigated the vertical movement of P from dairy manure and broiler litter through four Atlantic Coastal Plain soils. A randomized split‐plot design with two main‐plot tillage treatments (no tillage [NT] and chisel tillage [CH]) and five manure P rate split‐plot treatments was used at each location. The split‐plot P rates were 0, 100, 200, 300, and 400 kg P ha −1 yr −1 Four consecutive years of manure application began at all sites 5 yr before sampling. Soils were sampled to a depth of 150 cm from each split plot in seven depth increments and analyzed for soil test phosphorus (STP), water‐extractable soil phosphorus (WSP), and degree of phosphorus saturation (DPS). The DPS of the 0‐ to 15‐cm depths confirmed that at the 100 kg P ha −1 yr −1 application rate, all sites exceeded the threshold for P saturation (30%). At depths greater than 30 cm, DPS was typically below the 30% saturation threshold. The DPS change points ranged from 25 to 34% for the 0‐ to 90‐cm depths. Our research concluded that the risk of P leaching through the matrix of the Atlantic Coastal Plain soils studied was not high; however, P leaching via macropore bypass may contribute to P loss from these soils.