Modeling Solute Mass Exchange between Pore Regions in Slurry‐Injected Soil Columns during Intermittent Irrigation

• Published in: Vadose zone journal 2018, Vol.17 (1), p.1-10
• Main Authors: Glæsner, Nadia, Diamantopoulos, Efstathios, Magid, Jakob, Kjaergaard, Charlotte, Gerke, Horst H.
• Format: Article
• Language: English
• Subjects: Agricultural equipment; Agricultural land; Animal manures; Arable land; Boundary conditions; Columns (structural); Components; Exchanging; Experiments; Flow paths; Groundwater; Groundwater quality; Injection; Irrigation; Irrigation water; Leaching; Loam soils; Manures; Mass; Nutrient loss; Percolation; Plows; Pore water; Porosity; Predictions; Preferential flow; Rainfall; Regions; Scale models; Slurries; Soil; Soil columns; Soil porosity; Soil structure; Soils; Solute transport; Solutes; Steady flow; Surface water; Surface-groundwater relations; Topsoil; Transport; Unsaturated flow; Water bodies; Water flow
• ISSN: 1539-1663; 1539-1663
• DOI: 10.2136/vzj2018.01.0006

Core Ideas Water flow and solute transport models described solute leaching during slurry injection. Intermittent flow increased leaching of injected slurry compounds compared with steady flow. Mass exchange of slurry compounds during interruptions occurred from im‐ to mobile pore regions. Mass exchange between pore regions should be included in larger scale model predictions. Animal slurry application to agricultural land can be a threat to the quality of groundwater and nearby surface water bodies by percolation of solutes from slurry sources. We hypothesized that local‐scale processes, such as mass exchange between preferential flow paths and matrix pore regions, can play a substantial role in relation to slurry application and nutrient leaching. To improve understanding of these mass exchange mechanisms, soil column leaching data of nonreactive slurry components after injection of dairy slurry were analyzed under different initial and boundary conditions with single‐ and double‐porosity model approaches. The data set was from nine intact soil columns (20‐cm i.d., 20‐cm height) of the plow layer of arable loamy topsoil that were percolated under unsaturated steady‐flow conditions with a suction of 5 cm applied at the bottom. Both single‐ and double‐porosity water flow and mobile–immobile solute transport models could describe these experimental breakthrough curves. Rainfall interruptions mimicking more natural conditions and variably saturated intermittent flow led to higher leaching of injected slurry compounds than steady‐flow conditions. These observations could be explained by an increased mass exchange of dissolved injected slurry components from the immobile to the mobile pore water regions during interruptions. The results suggest that column tests under steady‐flow conditions could lead to false predictions of solute leaching after slurry injection in structured soils. Furthermore, local‐scale processes, such as mass exchange between pore regions, should be included in larger scale model predictions of nutrient losses from agricultural fields.