Download Changes over 13 years in carbon and soil fertility in Ferrosols in

FARMING SYSTEMS
Changes over 13 years in carbon and soil fertility in Ferrosols in Tasmania
L Sparrow 1, W Cotching 2, J Parry-Jones 3, G Oliver 3, E White 3 and R Doyle 3
TIA – Mt Pleasant Research Laboratories, 2TIAR – Cradle Coast Campus, 3TIAR – Sandy Bay
Campus
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Key Words: soil carbon change, cropping, Ferrosols
Take home messages
 Tasmanian farmers continue to increase the pH and phosphorus status of Ferrosols
 Increasing pressure to crop Ferrosols comes at the expense of organic carbon
 The data suggest a lower limit of about 2.5% organic carbon in Ferrosols under continuous
cropping on slopes less than 10%
Introduction
Ferrosols (red soils) are Tasmania’s prime agricultural soils and support a wide range of
enterprises including grazing, field crops and vegetables.
Objectives
To assess changes in organic carbon (OC), extractable phosphorus (P) and soil pH in 24 Ferrosols
used for agriculture in northern Tasmania.
Methods
Soil at each site was sampled in 1997, 2005 and 2010 at 2 depths: 0-150 mm and 150-300 mm.
Samples were analysed for Walkley-Black OC, Colwell P and pH 1:5 H2O. Histories of cultivation for
each site from 1973-2010 inclusive (38 years) were collected by interviewing farmers. Sites were
classified as continuously cropped (CC), intermittently cropped (IC) or pasture (P).
Results and outcomes
In 2010, CC sites had the lowest OC, and highest extractable P and pH at both depths. From 1997
to 2010, OC decreased and extractable P and pH increased at both depths. OC at both depths
decreased exponentially with increasing years of cultivation. Soils with the most OC in 1997 lost the
most OC in the next 13 years. At equivalent starting OC concentrations, CC soils lost more OC than
IC soils. Starting topsoil OC concentrations associated with zero change between 1997 and 2010
were 3.1% for IC sites and 2.5% for CC sites.
Funding and project duration
State and Federal governments, and TIA.
- 1997 - 2010
Technology transfer and publications
th
- Poster and associated paper presented to the 12 International Symposium on Soil and Plant
Analysis
Additional collaborators
- Participating farmers
Head down and tail up, Bill Cotching
samples with Garth Oliver.
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