The effects of the use of organic wastes on soil aggregation and structural stability

Agronomic practices often can lead to a consistent reduction of the organic matter (OM) content of soil promoting soil erosion and therefore the loss of the productive layer. Modern society produces a large amount of organic waste. These opposite trends, now independent, could be coupled in a unique sustainable natural cycle. In Italy, for example, olive oil mills waste waters (2 10-6 t y-1) could be an important source of OM for soil amelioration. The aim of this work is to study the effects of addition of these waste waters to soil. To pursue this goal, we examined the behaviour of this amendment with the more active fraction of soils, the clay, therefore we added waste water to a reference kaolinite and Ca¬bentonite. Wet and dry sieving has been used to assess the effects of amending on particle aggregates formation and their structural stability. DRIFT-IR spectroscopy has been employed to characterize OM evolution during the treatment. To evaluate the role of organic substances on the studied aggregation properties, a controlled incremental removal of OM was performed by low temperature ashing (LTA). This technique allows the oxidation of organics by oxygen plasma at low temperature (below 100 °C) with minimal disturbance of the mineral constituents. Our preliminary results show that olive oil mills waste waters used as amendments on clay samples increase aggregation and improve the water structural stability.