Structure evolution in arable soil after gypsum, structure lime and fibre sludge amendment

Soil conditioning aims at improving the physical, chemical and biological properties of soils and thereby serves as one measure to enhance crop productivity and to reduce water quality impacts of arable fields. In this study, we consider the effects of three soil amendments (gypsum, structure lime, and pulp and paper mill sludges) on soil structure development. The positive impacts of these amendments on erosion reduction have been observed in previous studies but detection of their effects on soil pore structure has turned out to be challenging. Here we studied the structural development of packed and sieved soil samples imitating topsoil after seedbed preparation using a ‘semifield’ approach. Arable topsoil (clay and OC contents were 38% and 2.4%, respectively) was mixed with the soil amendment, packed to perforated PVC cylinders (diameter 46 mm and height 70 mm) and buried in a field plot. The samples were removed from the field at certain times to quantify their structure with X-ray tomography and re-buried after the X-ray scanning. Our results show differences in the structure evolution during the first growing season for the considered treatments. The inorganic amendments (gypsum and structure lime) did not differ from the unamended control whereas fibre sludge had a clear impact on the structure evolution. Fibre amendment increased the porosity in the largest macropores (pore diameter > 1.2 mm) whereas the effects were opposite in smaller pore size classes (pore diameter < 0.6 mm). Our results indicate that soil amendments can influence the soil structure dynamics and thus soil functioning, but the effect depends on the amendment used.