Effects of agricultural management on sodosols in northern Tasmania

Abstract

Attributes of 25 Tasmanian sodosols were assessed using field and laboratory techniques to determine changes associated with 4 typical forms of agricultural management [long-term pasture, cropping with shallow tillage using discs and tines, cropping (including potatoes) with more rigorous and deeper tillage including deep ripping and powered implements, and cropping (including potatoes) where the potatoes were harvested when the soil was wet]. Soil organic carbon in the top 150 mm was 2.7% under long-term pasture compared 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 long-term pasture 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 tillage cropping compared with long-term pasture but decreased significantly in more rigorously tilled potato cropping paddocks. Aggregate stability in all cropped paddocks was nearly 50% less than in long-term pasture paddocks, with values in intensively tilled potato cropping paddocks approaching relatively low levels. Colwell extractable phosphorus (P) increased with all cropping, particularly after potatoes. Lower organic carbon and poorer physical properties were associated with paddocks which had grown potatoes, which adds weight to the view that cropping rotation and associated soil management practices are critical for sustainable management of Tasmanian sodosols. Farmers were surveyed about their views of the condition of their paddocks. They identified more healthy than unhealthy soil attributes under all management histories but reported more unhealthy soil attributes when potatoes were included in their rotation.

Influence of antecedent soil moisture on hydraulic conductivity in a series of texture‐contrast soils

“…For example, unpublished data by Cotching et al . () found the bulk density in the B21 of 27 Tasmanian Sodosols ranged from 1.02 g cm −3 to 1.72 g cm −3 . Greenwood et al .…”

“…Although Bruand and Gilkes (2002) reported subsoil bulk densities up to 1.91 g cm À3 in a cultivated Sodosol, values for clod density greater than 1.90 g cm À3 are generally higher than values of bulk density reported in the literature for the texture-contrast soils. For example, unpublished data by Cotching et al (2001) found the bulk density in the B21 of 27 Tasmanian Sodosols ranged from 1.02 g cm À3 to 1.72 g cm À3 . Greenwood et al (2006) reported bulk density of a Red Sodosol from northern Victoria ranged from 1.49 to 1.71 g cm À3 whilst clod density ranged from 1.58 to 1.65 at 30-40 cm depth.…”

Organic carbon in the silt + clay fraction of Tasmanian soils

“…The soils analysed in this study were pasture and cropped soils previously sampled from farm paddocks in northern Tasmania (latitude 41–42°S, longitude 146–148°E, mean annual temperature 11–12 °C, annual rainfall 600–1000 mm) (Sparrow et al. , 1999; Cotching et al. , 2001, 2004).…”

“…Further details of the sites, soil sampling and sample preparation are given in Sparrow et al. (1999) and Cotching et al. (2001, 2004.…”

Hydropedology and Preferential Flow in the Tasmanian Texture‐Contrast Soils

“…Estimates of the extent of texture‐contrast soils range from 17.0% (Isbell et al, 1997) to 20% of the Australian landmass (Northcote, 1979; Chittleborough, 1992), including around 80% of agricultural regions in southern Australia (Chittleborough et al, 1994) and approximately 60% of agricultural regions in southwestern Western Australia (Tennant et al, 1992). The texture‐contrast soils are associated with a range of management problems, including waterlogging, poor crop establishment, surface crusting, poor root penetration, desiccation, water repellence, wind erosion, tunnel erosion, salinity, poor nutritional status, hard setting, low infiltration, and poor water holding capacity (Edwards, 1992; Gardner et al, 1992; Tennant et al, 1992; Doyle and Habraken, 1993; Cotching et al, 2001; Hardie et al, 2007; Simeoni et al, 2009). Unlike other soil types, texture‐contrast soils contain an abrupt increase in clay content between the topsoil and the subsoil, which has been widely reported to result in the formation of seasonal perched water tables and subsurface lateral flows (Turner et al, 1987; Gregory et al, 1992; Naidu et al, 1993; Chittleborough et al, 1994; Cox and McFarlane, 1995; Fleming and Cox, 1998; Stevens et al, 1999; Eastham et al, 2000; Cox and Pitman, 2001; Cox et al, 2002; Ticehurst et al, 2003, 2007).…”