Track 2-05: Carbon Sequestration and Cycling

Description

The natural spatial variability in soil organic carbon (SOC) found under perennial pasture systems can make it difficult to determine differences between contrasting agricultural management practices. Pasture composition in large, extensively grazed paddocks can give an indication of pasture growth, utilisation and fertility that influence SOC and are a result of management over the longer-term. This paper examines SOC stocks on the central and southern tablelands of NSW, Australia (average rainfall from 615 to 915 mm and average annual temperature from 10.6 to 15.6°C) at three scales (regional, between similar sites and within site) to determine the influence of management, pasture composition, herbage mass and root mass. After allowing for variability due to climate, landscape and soil properties there were no differences in management comparisons, e.g. high v low fertiliser input, introduced v native pastures and rotational grazing v set stocking. The total herbage mass measured at the time of sampling had a significant relationship with SOC between and within sites and the presence of some species was associated with lower SOC. Root mass measured at an intensively monitored site showed a significant relationship with SOC. These results reflect the complexity of grazing/pasture systems, with natural variability explaining most of the variability in SOC stock; and pasture productivity leading to higher root production explaining differences in SOC levels rather than grazing management.

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The Effects of Management and Vegetation on Soil Carbon Stocks in Temperate Australian Grazing Systems

The natural spatial variability in soil organic carbon (SOC) found under perennial pasture systems can make it difficult to determine differences between contrasting agricultural management practices. Pasture composition in large, extensively grazed paddocks can give an indication of pasture growth, utilisation and fertility that influence SOC and are a result of management over the longer-term. This paper examines SOC stocks on the central and southern tablelands of NSW, Australia (average rainfall from 615 to 915 mm and average annual temperature from 10.6 to 15.6°C) at three scales (regional, between similar sites and within site) to determine the influence of management, pasture composition, herbage mass and root mass. After allowing for variability due to climate, landscape and soil properties there were no differences in management comparisons, e.g. high v low fertiliser input, introduced v native pastures and rotational grazing v set stocking. The total herbage mass measured at the time of sampling had a significant relationship with SOC between and within sites and the presence of some species was associated with lower SOC. Root mass measured at an intensively monitored site showed a significant relationship with SOC. These results reflect the complexity of grazing/pasture systems, with natural variability explaining most of the variability in SOC stock; and pasture productivity leading to higher root production explaining differences in SOC levels rather than grazing management.