Influence of Long‐term Application of Feedlot Manure Amendments on Water Repellency of a Clay Loam Soil

Long‐term application of feedlot manure to cropland may increase the quantity of soil organic carbon (C) and change its quality, which may influence soil water repellency. The objective was to determine the influence of feedlot manure type (stockpiled vs. composted), bedding material (straw [ST] vs. woodchips [WD]), and application rate (13, 39, or 77 Mg ha−1) on repellency of a clay loam soil after 17 annual applications. The repellency was determined on all 14 treatments using the water repellency index (R index), the water drop penetration time (WDPT) method, and molarity of ethanol (MED) test. The C composition of particulate organic matter in soil of five selected treatments after 16 annual applications was also determined using 13C nuclear magnetic resonance–direct polarization with magic‐angle spinning (NMR‐DPMAS). Manure type had no significant (P > 0.05) effect on R index and WDPT, and MED classification was similar. Mean R index and WDPT values were significantly greater and MED classification more hydrophobic for WD than ST. Application rate had no effect on the R index, but WDPT was significantly greater and MED classification more hydrophobic with increasing application rate. Strong (r > 0.7) but nonsignificant positive correlations were found between R index and WDPT versus hydrophobic (alkyl + aromatic) C, lignin at 74 ppm (O‐alkyl), and unspecified aromatic compounds at 144 ppm. Specific aromatic compounds also contributed more to repellency than alkyl, O‐alkyl, and carbonyl compounds. Overall, all three methods consistently showed that repellency was greater for WD‐ than ST‐amended clay loam soil, but manure type had no effect. Core Ideas Feedlot manure type had no influence on soil water repellency. Soil water repellency was greater for woodchip than straw‐amended soils. Soil water repellency increased with greater application rates. Soil water repellency was most positively correlated with aromatic C group and compounds. Soil water repellency was generally greater for amended than unamended soils.