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Changes in organic carbon and selected soil fertility parameters in agricultural soils in Tasmania, Australia


Sparrow, L and Cotching, B and Parry-Jones, J and Oliver, G and White, E and Doyle, R, Changes in organic carbon and selected soil fertility parameters in agricultural soils in Tasmania, Australia, Communications in Soil Science and Plant Analysis, 44, (1-4) pp. 166-177. ISSN 0010-3624 (2013) [Refereed Article]

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Copyright 2013 Taylor and Francis

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DOI: doi:10.1080/00103624.2013.736258


Twenty-four sites in northern Tasmania on Ferrosols formed on Tertiary basalt were sampled in 1997, 2005, and 2010. The farming systems at the sites during this period were either (a) continuous pasture, (b) continuous cropping of vegetable, cereal, and other cash crops in rotation, or (c) a mix of pasture and cropping (intermittent cropping). Average organic carbon (OC) concentrations across all sites and both sample depths (0150 mm and 150300 mm) decreased from 4.0% in 1997 to 3.5% in 2005 and 3.3% in 2010 (P < 0.001). Average OC was greater at 0150 mm (4.1%) than at 150300 mm (3.1%) (P < 0.001). Average total soil nitrogen (N) in 2010 (0.42%) at 0150 mm was not significantly different (P = 0.07) from the average in 1997 (0.38%). Soil pH in water (pHw) showed the opposite trend to OC, increasing with time from 6.0 in 1997 to 6.2 in 2010. This reflects the consistent use of calcite and dolomite in Tasmanian farming because the natural pHw of these soils is less than 5.5. Exchangeable calcium and magnesium were also greater in 2010 compared with 1997. Bicarbonate-extractable phosphorus (P) averaged across both depths increased (P < 0.001) steadily from 77 mg kg−1 in 1997 to 95 mg kg−1 in 2005 to 126 mg kg−1 in 2010. At the five sites that remained under continuous cropping throughout the study, average 2010 OC in the topsoil was 3.2%, a decrease of 0.5% since 1997; pHw was unchanged at 6.4; and bicarbonate-extractable P increased by an average of 73 mg kg−1 to 211 mg kg−1. For the three sites that remained in pasture the corresponding topsoil changes were 0.3% less OC to an average of 4.8%; pHw 0.4 units greater at 6.0; and 41 mg kg−1 more bicarbonate-extractable P to an average of 99 mg kg−1. At the six sites converted from continuous pasture to intermittent cropping the average 2010 topsoil OC was 4.5%, a loss of 1.3%; pHw increased by 0.5 units to 6.1; and bicarbonate-extractable P increased by 35 mg kg−1 to 97 mg kg−1. There was a highly significant (R2 = 0.82) exponential relationship between topsoil OC in 2010 and the number of years each site had been cropped during the 38 years 19722010, for which reliable records were available (OC = 4.933e−0.018years), which suggested an equilibrium topsoil OC concentration of about 2.5% under continuous cropping on these soils. These results indicate that Tasmanian farmers on Ferrosols continue to increase the pHw and P fertility of their soils and that increasing cropping intensity on these soils comes at the expense of soil carbon.

Item Details

Item Type:Refereed Article
Keywords:carbon, cropping frequency, equilibrium, nitrogen, oxisols, pH, phosphorus
Research Division:Environmental Sciences
Research Group:Soil sciences
Research Field:Soil sciences not elsewhere classified
Objective Division:Environmental Management
Objective Group:Terrestrial systems and management
Objective Field:Terrestrial systems and management not elsewhere classified
UTAS Author:Sparrow, L (Dr Leigh Sparrow)
UTAS Author:Cotching, B (Dr Bill Cotching)
UTAS Author:Parry-Jones, J (Ms Jocelyn Parry-Jones)
UTAS Author:Oliver, G (Mr Garth Oliver)
UTAS Author:White, E (Ms Eve White)
UTAS Author:Doyle, R (Associate Professor Richard Doyle)
ID Code:79769
Year Published:2013
Web of Science® Times Cited:4
Deposited By:Tasmanian Institute of Agriculture
Deposited On:2012-10-02
Last Modified:2017-10-31

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