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Rapid internal drainage rates in Ferrosols

Bell, M.J. and Bridge, B.J. and Harch, G.R. and Orange, D.N. (2005) Rapid internal drainage rates in Ferrosols. Australian Journal of Soil Research, 43 (4). pp. 443-455.

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Article Link(s): http://dx.doi.org/10.1071/SR04063

Publisher URL: http://www.publish.csiro.au/

Abstract

Adoption of conservation tillage practices on Red Ferrosol soils in the inland Burnett area of south-east Queensland has been shown to reduce runoff and subsequent soil erosion. However, improved infiltration resulting from these measures has not improved crop performance and there are suggestions of increased loss of soil water via deep drainage. This paper reports data monitoring soil water under real and artificial rainfall events in commercial fields and long-term tillage experiments, and uses the data to explore the rate and mechanisms of deep drainage in this soil type.

Soils were characterised by large drainable porosities (≥0.10 m3/m3) in all parts of the profile to depths of 1.50 m, with drainable porosity similar to available water content (AWC) at 0.25 and 0.75 m, but >60% higher than AWC at 1.50 m. Hydraulic conductivity immediately below the tilled layer in both continuously cropped soils and those after a ley pasture phase was shown to decline with increasing soil moisture content, although the rate of decline was much greater in continuously cropped soil. At moisture contents approaching the drained upper limit (pore water pressure = -100cm H2O), estimates of saturated hydraulic conductivity after a ley pasture were 3-5 times greater than in continuously cropped soil, suggesting much greater rates of deep drainage in the former when soils are moist.

Hydraulic tensiometers and fringe capacitance sensors monitored during real and artificial rainfall events showed evidence of soils approaching saturation in the surface layers (top 0.30-0.40 m), but there was no evidence of soil moistures exceeding the drained upper limit (i.e. pore water pressures ≤ -100 cm H2O) in deeper layers. Recovery of applied soil water within the top 1.00-1.20 m of the profile during or immediately after rainfall events declined as the starting profile moisture content increased. These effects were consistent with very rapid rates of internal drainage. Sensors deeper in the profile were unable to detect this drainage due to either non-uniformity of conducting macropores (i.e. bypass flow) or unsaturated conductivities in deeper layers that far exceed the saturated hydraulic conductivity of the infiltration throttle at the bottom of the cultivated layer. Large increases in unsaturated hydraulic conductivities are likely with only small increases in water content above the drained upper limit. Further studies with drainage lysimeters and large banks of hydraulic tensiometers are planned to quantify drainage risk in these soil types.

Item Type:Article
Corporate Creators:Department of Employment, Economic Development and Innovation (DEEDI), Agri-Science, Plant Science, Crop and Food Science
Business groups:Agri-Science, Crop and Food Science
Additional Information:Reproduced with permission from © CSIRO Publishing. Access to published version may be available via Publisher’s website.
Keywords:Macropores; runoff; salinity; water balance; infiltration; salinity measurement; soil conservation; water pollution; moisture contents; soils; drainage; soil water.
Subjects:Agriculture > Agriculture (General) > Soil conservation and protection
Agriculture > Agriculture (General) > Soils. Soil science
Deposited On:02 Mar 2009 00:16
Last Modified:10 Oct 2011 06:35

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