You have full access to this open access article. Heterogeneous flow pathways through the soil determine the transport of dissolved and particle-bound nutritional elements like phosphorus P to ground and surface waters. This study was designed to understand the spatial patterns of P in agriculturally used soils and the mechanisms causing P accumulation and depletion at the centimetre scale.
The plant-available P was analysed using double lactate extraction DL-P. We conclude that P tends to accumulate along flow pathways in the topsoil in the observed fertilized and tilled mineral soil. In contrast, in the subsoil at a generally lower P level, P is depleted from the prominent macroporous flow domains. Phosphorus P is a major cause of eutrophication and surface water quality impairment. The agriculturally based non-point source pollution of water bodies is gaining more and more importance with the diminishing of point sources and the upgrade of sewage systems Jarvie et al.
For a long time, it was the general opinion that P, because of its strong affinity to soil particles, is mainly transported at the soil surface in an erosive manner Daniel et al. Today, we know that the rapid transport of P along preferential flow pathways vertically through the soil profile is an environmental threat, especially at tile-drained field sites where shallow ground and surface waters are directly connected King et al.
The mitigation of the diffuse P export from agricultural fields and an improved P use efficiency are critical future challenges for farmers and environmental agencies Kleinman et al. Water movement in soils regulates the transport of dissolved and particle-bound nutrients and contaminants Rozemeijer et al. Solute transport takes place through the soil matrix e. Also, hydrological factors like rainfall intensity, duration, and soil moisture affect water and solute transport.
In the case of a preferential transport situation, water flow bypasses the main parts of the porous soil matrix. Likewise, bypass flow reduces the time for the desorption of P from the soil. Thus, several separate terms were introduced to better describe the flow and transport situation. For instance, macropore flow occurs along continuous earthworm burrows, root channels, fissures, or cracks.
