Soil Structural Shifts Caused by Land Management Practices ^†

Abstract

Long-term agricultural practices have been shown to affect soil hydro-physical properties in multiple ways. They affect the stability and distribution of soil aggregates leading to changes in water retention, bulk density, hydraulic conductivity, and porosity. Aggregate stability is an indicator of the resilience of aggregates to external forces. Unstable aggregates can change rapidly under different land management practices and meteorological conditions. Μacro-aggregates (>250 μm) are formed more rapidly and are often more sensitive to management changes. Here, four different long-term experiments, run by the SoilCare Horizon 2020 Project partners, were sampled and analyzed, in order to evaluate the impact of different agricultural management practices in the water stability of soil aggregates and the fractions distribution. Different experiments selected, include control-conventional treatment and different treatments, which are considered soil improving. The treatments are about soil cultivation (conventional ploughing-control, zero tillage, minimum tillage, strip tillage, shallow tillage) and organic input (mineral fertilization-control, residue incorporation, farmyard manure) and are selected in areas with different climatic and soil conditions. Initial results indicate that treatments with less soil disturbance present more water stable aggregates (WSA) >250 μm and higher mean weight diameters (MWD), as well as the same trend following the treatments with increased organic input. According to Tukey’s Honest Significance test (p < 0.05), management practices are shown to have a significant impact on the WSA and MWD in most cases, but not all similar treatments in the different areas present the same results. The large macro-aggregates (>2 mm) seem to be greatly sensitive to soil cultivation, whereas the results for the small macro-aggregates (250 μm–2 mm) are controversial among the different tillage experiments. The different organic inputs seems to affect more the small macro-aggregates than the larger. The initial results indicate that the shifts in the soil structure cannot only be justified by the different management practices. The interrelationships and potential links with other soil properties like texture, bulk density, particulate organic matter and climate will be taken into account in further steps in order to understand the mechanisms behind the aggregation shifts.