Method for in situ measurements of water, sediment and phosphorous transport in the upper soil profile

Research on transport processes involved in P losses by subsurface flow, including artificial drainage, is becoming increasingly important. An improved understanding of the processes involved in sediment detachment and P mobility in the soil profile is needed in order to develop proper management strategies for P control. The objective of this article is to present the development of a field lysimeter technique, and a complementary laboratory pinhole test on undisturbed soil samples, that can be used to assess rates and mechanisms involved in water, sediment and phosphorus transport in the upper soil profile at different rainfall intensities. The study, performed on a silty clay, consisted of three parts: (1) pre-test of a new field lysimeter approach with the aim to observe water flow patterns and difficulties related to preparation and set-up, (2) evaluation of the improved field lysimeter methodology, which consisted of a rain simulator above ground, the soil profile through which the applied water percolated, and a collection tray at 40-50 cm depth from which the drain water and sediment was sampled, (3) evaluation and development of the pinhole test for assessing soil resistance to internal erosion. The pre-tests gave promising results and the improved field lysimeter showed interesting temporal responses, at two consecutive rain simulation intensities, in outflow rates of water, bromide, lithium, total P and dissolved P. The pinhole test was run on undisturbed samples with three different water contents and at three different applied positive pressure heads and showed fast peaks in turbidity following start of each run. Combining measurements from the in situ field lysimeter and pinhole approaches presented in this article has the potential to be valuable in detecting critical parameters that control the processes leading to subsurface leaching of P to deeper soil layers.