Preferential flow and transport through macropores affect plant water use efficiency and enhance leaching of agrochemicals and the transport of colloids, thereby increasing the risk for contamination of groundwater resources. The effects of soil compaction, expressed in terms of bulk density (BD), and organic carbon (OC) content on preferential flow and transport were investigated using 150 undisturbed soil cores sampled from 15 × 15–m grids on two field sites. Both fields had loamy textures, but one site had significantly higher OC content. Leaching experiments were conducted in each core by applying a constant irrigation rate of 10 mm h−1 with a pulse application of tritium tracer. Five percent tritium mass arrival times and apparent dispersivities were derived from each of the tracer breakthrough curves and correlated with texture, OC content, and BD to assess the spatial distribution of preferential flow and transport across the investigated fields.
Soils from both fields showed strong positive correlations between BD and preferential flow. Interestingly, the relationships between BD and tracer transport characteristics were markedly different for the two fields, although the relationship between BD and macroporosity was nearly identical. The difference was likely caused by the higher contents of fines and OC at one of the fields leading to stronger aggregation, smaller matrix permeability, and a more pronounced pipe-like pore system with well-aligned macropores.
1Department of Agroecology, Faculty of Science and Technology, Aarhus University, Tjele, Denmark.
2Requimte, Instituto Superior de Engenharia do Porto, Instituto Politécnico do Porto, Porto, Portugal.
3Department of Biotechnology, Chemistry and Environmental Engineering, Aalborg University, Aalborg, Denmark.
4Department of Soil, Water and Environmental Science, University of Arizona, Tucson, Arizona, USA.
Address for correspondence: António Carlos Alves Soares, Blichers Allé 20, PO Box 50, DK-8830 Tjele, Denmark. E-mail: email@example.com
Financial Disclosures/Conflicts of Interest: This research was funded as part of the large framework project Soil Infrastructure, Interfaces and Translocation Processes in Inner Space (“Soil-It-Is”) by the Danish Research Council for Technology and Production Sciences, by the Danish Pesticide Leaching Assessment Programme (http://www.pesticidvarsling.dk), by the European Union (FEDER funds through COMPETE), and by the Fundação para a Ciência e Tecnologia through project Pest-C/EQB/LA0006/2013. António Soares is grateful to FCT for his doctoral research grant (SFRH/BD/69565/2010) financed by POPH-QREN, Tipologia 4.1 e Formação Avançada, subsidized by Fundo Social Europeu and Ministério da Ciência, Tecnologia e Ensino Superior.
Received July 16, 2014.
Accepted for publication January 26, 2015.