Mitigation of critical transport pathways for phosphorus from common marine clay soil
Losses of phosphorus from agricultural land continue to cause serious environmental problems. Local scale soil properties, such as macroporosity, are crucial for such leaching e.g. in cracking clay soils of marine origin common around the Baltic Sea. The transport of water, gases and solutions is controlled by the soil structure and the properties of the pore space. The composition and continuity of a pore or pathway may be more important than its size.
The aim of this project is evaluating the spatial variation in the macropore network and in transport properties within the lake Bornsjön experimental field to assess options for mitigating phosphorus leaching with management practices changing the soil structure.
The work will concentrate on the top soil which is the part of the arable land that is directly influenced by crop growth and management practices. Thirty-two soil columns will be taken from the top soil in experimental plots treated with four different farming practices: conventional autumn ploughing, structural liming, shallow autumn tillage and, for reference, unfertilized fallow. The experimental site which consists of clay soil, is located near Lake Bornsjön in south east Sweden.
The strength of preferential flow and P transport through the soil pore network will be evaluated using laboratory measurements on soil samples from the four different treatments. Quantitative indicators of soil structure will be derived from 3-dimentional X-ray tomography images of these samples. To describe and predict solute transport in soil, simulated rainfall experiments will be carried out on the soil samples where a pulse of tracer solution will be applied to each column under controlled water flow conditions. Breakthrough curves (BTCs) are then measured by recording the tracer concentrations in the outflow system.
The physically based MACRO-model will be used in model scenarios for pesticide leaching based on the results from the experimental study to assess pesticide leaching risks for the different farming practices. Model parameters describing the macropore system in the topsoil will be obtained from X-ray images, calibration against column tracer breakthrough data and water flow data from the field experiment.