Short-term legacy effects of feedlot manure amendments on water-extractable organic carbon in a clay loam soil profile

Limited research exists on legacy effects of land application of feedlot manure on accumulation, redistribution, and leaching potential of water-extractable organic carbon (WEOC) in soil profiles. We sampled a clay loam soil at six depths (0-1.50 m) 2 yr after the last application (2014) of 17 continuous annual manure applications (since 1998). The amendment treatments were stockpiled (SM) or composted (CM) feedlot manure containing straw (ST) or wood-chip (WD) bedding at three application rates (13, 39, and 77 Mg ha(-1) dry basis). There was also an unamended control (CON) and inorganic fertilizer (IN) treatment. The soil samples were analyzed for concentrations of WEOC. The total mass or accumulation of WEOC in the soil profile was greater (P <= 0.05) by 1.2-3.3 times for the CM-ST-77 treatment than 12 of 14 other treatments, and it was significantly greater for amended than CON or IN treatments. The total WEOC mass was 14%-20% greater for CM-ST than CM-WD, SM-ST, and SM-WD treatments, and it was 16%-22% greater for CM than SM at the 39 and 77 Mg ha(-1) rates. The 77 Mg ha(-1) rate of the four manure type-bedding treatments had the significantly greatest (by 37%-527%) concentrations of WEOC at the six depths compared with other treatments, suggesting greater redistribution and leaching potential. Significant manure effects occurred on soil WEOC 2 yr after the manure was last applied following 17 continuous applications, and it indicated an increased risk of leaching potential at the higher application rate.