Agricultural management has a well-understood effect on total soil organic matter (OM) content. However, the spatial distribution of that OM within soil is not fully understood, and this is likely to control a range of vital soil and ecosystem functions including soil fertility, flood control and climate change mitigation. We aim to assess the effect of long-term agricultural management on the spatial distribution of OM in arable soil by developing a neutron tomography method to visualise the OM in three dimensions at the micro-scale, and then applying this to soil core samples taken from the famous long-term agricultural experiments at Rothamsted Research (UK). We will link farm practices that have altered the soil OM content, such as fertiliser and manure applications, to spatial patterns, and consequently to other soil properties and crop yield on these well-characterised experiments.