THE STRUCTURE OF 2 ALLUVIAL SOILS IN ITALY AFTER 10 YEARS OF CONVENTIONAL AND MINIMUM TILLAGE

Micro and macroporosity, pore shape and size distribution, aggregate s tability, saturated hydraulic conductivity and crop yield were analyse d in alluvial silty loam (Fluventic Eutrochrept) and clay soils (Verti c Eutrochrept) following long-term minimum and conventional tillage. T he soil structure attributes were evaluated by characterizing porosity by means of image analysis of soil thin sections prepared from undist urbed soil samples. The interaggregate microporosity, measured by merc ury intrusion porosimetry, increased in the minimally tilled soils, wi th a particular increase in the storage pores (0.5-50 mu m). The amoun t of elongated transmission pores (50-500 mu m) also increased in the minimally tilled soils. The resulting soil structure was more open and more homogeneous, thus allowing better water movement, as confirmed b y the greater hydraulic conductivity of the minimally tilled soils. Th e aggregate stability was less in the conventionally tilled soils and this resulted in a greater tendency to form surface crusts and compact ed structure, compared with the minimally tilled soils. The latter til lage practice seemed to maintain, in the long-term, better soil struct ure conditions and, therefore, maintain favourable conditions for plan t growth, In the silt loam, the crop yield did not differ significantl y between the two tillage systems, while in the clay soil it decreased in the minimum tilled soil because of problems of seed bed preparatio n at the higher surface layer water content.