Effects of agricultural management on sodosols in northern Tasmania

Attributes of 25 Tasmanian sodosols were assessed using field and laborator y techniques to determine changes associated with 4 typical forms of agricu ltural management [long-term pasture, cropping with shallow tillage using d iscs and tines, cropping (including potatoes) with more rigorous and deeper tillage including deep ripping and powered implements, and cropping (inclu ding potatoes) where the potatoes were harvested when the soil was wet]. So il organic carbon in the top 150 mm was 2.7% under long-term pasture compar ed with 1.8% in rigorously tilled cropping paddocks, and microbial biomass C values were 194 and 129 mg/kg, respectively. Readily oxidisable organic C concentrations were 1.8 mg/g and 1.3 mg/g, respectively. Infiltration rate was greater in paddocks with shallow tillage cropping than longterm pastur e but was 43% less in paddocks which had grown potatoes and 70% less after a wet potato harvest. Dry aggregate-size showed no change under shallow til lage cropping compared with long-term pasture but decreased significantly i n more rigorously tilled potato cropping paddocks. Aggregate stability in a ll cropped paddocks was nearly 50% less than in long-term pasture paddocks, with values in intensively tilled potato cropping paddocks approaching rel atively low levels. Colwell extractable phosphorus (P) increased with all c ropping, particularly after potatoes. Lower organic carbon and poorer physi cal properties were associated with paddocks which had grown potatoes, whic h adds weight to the view that cropping rotation and associated soil manage ment practices are critical for sustainable management of Tasmanian sodosol s. Farmers were surveyed about their views of the condition of their paddoc ks. They identified more healthy than unhealthy soil attributes under all m anagement histories but reported more unhealthy soil attributes when potato es were included in their rotation.