Iversen, Bo Vangsø9; Berisso, Feto Esimo9; Schjønning, Per9; Wildenschild, Dorthe5; de Jonge, Lis Wollesen9; Etana, Ararso6; Jarvis, Nicholas J.6; Larsbo, Mats7; Keller, Thomas7; Arvidsson, Johan6; Børgesen, Christen Duus10
1 Department of Agroecology and Environment, Faculty of Agricultural Sciences, Aarhus University, Aarhus University2 Soil physics and Soil resources, Faculty of Agricultural Sciences, Aarhus University, Aarhus University3 Agrohydrology and Water Quality, Faculty of Agricultural Sciences, Aarhus University, Aarhus University4 Department of Agroecology - Soil Physics and Hydropedology, Department of Agroecology, Science and Technology, Aarhus University5 Oregon State University, Corvallis, OR6 Department of Soil and Environment, SLU, UPPSALA7 Agroscope Research Station ART, Zürich8 Department of Agroecology - Climate and Water, Department of Agroecology, Science and Technology, Aarhus University9 Department of Agroecology - Soil Physics and Hydropedology, Department of Agroecology, Science and Technology, Aarhus University10 Department of Agroecology - Climate and Water, Department of Agroecology, Science and Technology, Aarhus University
Soil compaction is a major threat to sustainable soil quality and is increasing since agricultural machinery is becoming heavier and is used more intensively. Compaction not only reduces pore volume, but also modifies the pore connectivity. The inter-Nordic research project POSEIDON (Persistent effects of subsoil compaction on soil ecological services and functions) put forward the hypothesis that due to a decrease in the hydraulic conductivity in the soil matrix, compaction increases the frequency of preferential flow events in macropores and therefore increases the leaching of otherwise relatively immobile agrochemicals. In a morainic clay soil, undisturbed soil cores (6280 cm3) were sampled at 20-40 and 60-80 cm depth in the spring 2009 fourteen years after operation with a heavy sugar beet harvester. Soil cores were sampled both from uncompacted reference blocks and from compacted blocks. In the field the near-saturated hydraulic conductivity was measured with a tension infiltrometer in the same treatments at a depth of 30 cm. In the laboratory saturated and near-saturated hydraulic conductivity and the bulk density were measured as well. Also, macropores in the large soil cores were made visible by CT scans performed at a water content at field capacity. Prior to the soil sampling campaign, measurements of mechanical strength in terms of cone penetration resistance gave a clear indication of lasting compaction effects below the plough layer. Measurements on the soil columns showed that for the upper soil depth, a significant increase in bulk density was measured for the compacted treatment. For the lower depth differences were less pronounced. For the saturated hydraulic conductivity, the results indicated a decrease of the hydraulic conductivity for the compacted treatment for the upper depth whereas the near-saturated hydraulic conductivity did not show any significant differences between treatments at the two depths due to a high variability between measurements. Results from the measurements with the tension infiltrometer were in accordance with the hydraulic conductivity measured in the laboratory showing no difference in the hydraulic conductivity at low matric potentials, but with a tendency for larger values of the conductivity in the reference blocks at matric potentials close to saturation. Results from the CT scans were in accordance with the measurements of bulk density showing a significant trend of reduced macroporosity for the compacted upper depth. We conclude that the measured changes in the analyzed transport parameters support our hypothesis that the colloid-facilitated transport of agrochemicals in spatially connected macropores leads to a higher risk of contamination of water bodies under compacted agricultural soils.
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ASA, CSSA, and SSSA 2010 International Annual Meetings