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Source: F.Robinson (DEPI), August 2012 Executive Summary As part of the Soil Carbon Research Program (SCaRP), the objective of this study was to measure soil carbon stocks and composition in pasture and cropping systems of Victoria (dairy, beef, sheep and cereal production) and determine the influence of management in regions with varying climate and soil type. Soil carbon stocks were measured, using the standardised SCaRP methodology, at 861 sites; 602 from farms and 259 from established field trials. The farm sites were selected according to region, soil type, and management system, with approximately 25 representations of each region x soil x management combination. Average annual rainfall in the regions ranged from <300 mm to >1000 mm. The field trials included cropping systems comparing cultivation, stubble management and rotation treatments, and livestock systems comparing pasture type, fertiliser and grazing management treatments. The trials had been established for periods of between 5 and 94 years. The dataset is as yet incomplete and this report presents provisional results. Soil organic C stocks in the 0.3 m depth varied widely across the pasture and cropping systems of Victoria. Average total organic C stocks (0-0.3 m depth) in the regions were in the order: Mallee (15 Mg C/ha) < Northern Wimmera (29 Mg C/ha) < Southern Wimmera (33 Mg C/ha) < Northern and Southern Slopes (40 Mg C/ha) < Victorian Volcanic Plains (65 Mg C/ha) < Eastern Plains (80 Mg C/ha) < Strzelecki Ranges (90 Mg C/ha) < Otways (165 Mg C/ha). Soil organic C stocks were strongly related to annual rainfall and to EVI (Enhanced Vegetation Index). Total organic C stocks varied with soil type in the order: Tenosol (8 Mg C/ha) < Calcarosol (26 Mg C/ha) < Sodosol (41 Mg C/ha) < Vertosol (48 Mg C/ha) < Chromosol (53 Mg C/ha) < Dermosol (106 Mg C/ha). Soil total organic C stocks varied with management in the order: continuous cropping (34 Mg C/ha) < crop-pasture rotation (45 Mg C/ha) < sheep/beef pasture (63 Mg C/ha) < dairy pasture (120 Mg C/ha). Results from the field trials showed that management practices such as fertiliser application, cultivation, stubble retention, crop rotations and grazing management had relatively small or no effects on soil organic C stocks. Carbon stocks were always greater in the 0-0.1 m depth than in the 0.1-0.2 and 0.2-0.3 m depths. The compositon of the soil organic C stocks varied considerably, but averaged 24% particulate C, 54% humic C and 29% resistant C. The wide variation in soil organic C stocks in Victoria reflects inter-relationships between climate, management and soil properties. As such, baseline soil organic C stocks cannot be inferred from management, regional or soil classes alone. |
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Page Updated: September 2013 |
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