Water Repellency and Hydrophobicity of Some Major Agricultural Crop Residues

Abstract

Water repellency of agricultural crop residues may affect the hydrologic balance and increase runoff loss of pesticides by greater wash off from hydrophobic residue. We conducted a laboratory study to measure water repellency and hydrophobicity of 30 major agricultural crops (grass, legume, cereal, oilseed, pulse, and specialty crops). Crop samples were collected in southern Alberta, Canada in 2017 and 2018. Water repellency (WR) of oven‐dried (60°C) and ground (<2 mm) crop residues was measured using the water drop penetration time (WDPT) and molarity of ethanol (MED) tests. Hydrophobicity was evaluated using the ratio of hydrophobic CH– to hydrophilic CO–functional groups using Fourier Transform Infrared (FTIR) spectroscopy. The WDPTs of the 30 agricultural crops ranged from 8.3 to 2438 s, suggesting that crop species influenced WR of the dried and undecomposed residues. Needle‐and‐thread grass (Stipa comata Trin. and Rupr.), blue grama (Bouteloua gracilis [Kunth] Lag. ex Griffiths), and western wheatgrass (Agropyron smithii Rydb.) were the most WR crops based on WDPT. Fababean (Vicia faba), mustard (Sinapis alba L.), and sweet clover (Melilotus officinalis) were the least WR crops. Mean WDPTs were significantly (P ≤ 0.05) greater for grass than the other four crop types by 23 to 44 times. Significant differences in WDPT occurred among crop species within each of the six crop types. A significant positive correlation occurred between WDPT and hydrophobicity (r = 0.54), but not between WDPT and organic carbon. Overall, crop type and species may influence WR of crop residues and could affect the hydrologic balance.Core Ideas Agricultural crop species residue influenced water repellency and hydrophobicity Grass was the most water repellent and hydrophobic crop type A positive correlation occurred between water repellency and hydrophobicity The physical morphology of leaves may contribute to water repellency Water repellency differences also occurred for species within the six crop types