Soil carbon dynamics under different cropping and pasture management in temperate Australia: Results of three long-term experiments

Abstract

In addition to its important influence on soil quality and therefore crop productivity, soil organic carbon (SOC) has also been identified as a possible C sink for sequestering atmospheric carbon dioxide. Limited data are available on the impact of management practices on the rate of SOC change in agricultural soils in Australia. In this paper, results of three long-term trials (13-25 years) located near Wagga Wagga in temperate Australia were used to assess C dynamics under different tillage and stubble management practices, and under cropping intensities in pasture/crop rotations.Experimental results confirm the importance of management practices and pasture in determining first the steady-state SOC concentrations that are characteristic of given rotations and crop management systems, and second the rates of change of SOC concentrations as they approach steady-state concentrations in agricultural soils of this agro-ecological zone. A long-term crop/pasture experiment at a site with initial high SOC showed that the rate of SOC change in different treatments ranged from -278 to +257 kg C/ha.year over 0-0.3 m soil depth. Under continuous cropping, even under conservation agriculture practices of no-tillage, stubble retention, and crop rotation, the high initial SOC stock (0-0.3 m) present after a long-term pasture phase was, at best, maintained but tended to decrease with increased tillage or stubble burning practices. The effect of tillage was greater than that of stubble management. Increases in SOC were observed only in rotations incorporating a pasture phase.Our results suggest that improved soil nutrient and grazing management of permanent pasture can lead to an increase of 500-700 kg C/ha.year where the initial SOC concentrations are well below steady-state concentrations that could be expected after long periods of improved management. No difference was found between perennial pasture and annual pasture to the depth measured (0-0.3 m). Our results suggest that pasture holds the key to maintaining, and even increasing, SOC under crop/pasture in this environment.

Soil organic carbon concentrations and storage in irrigated cotton cropping systems sown on permanent beds in a Vertosol with restricted subsoil drainage

“…Hulugalle et al (2011) suggested that N fertiliser inputs, depth of soil disturbance, annual temperatures, and winter rainfall were more closely related to carbon gains and losses than was time. Although some authors have claimed carbon sequestration rates of~2 Mg C ha -1 year -1 or more in the surface 0.3 m of semi-arid irrigated Vertosols, our results do not support this view but concur with most of the studies conducted in irrigated and dryland row-cropped farming systems under semi-arid conditions (Hulugalle 2000;Luo et al 2010;Sanderman et al 2010;Chan et al 2011;Powlson et al 2011;White 2012).…”

“…Under semi-arid conditions, however, significant and sustained sequestration of carbon has been reported primarily for farming systems with perennial crops and pastures (Luo et al 2010;Sanderman et al 2010;Chan et al 2011;Powlson et al 2011). Although some benefits have been reported for conservation farming practices such as zero-tillage and crop rotation, carbon sequestration rates have generally been low and subject to variables such as water and nutrient availability, temperature, soil condition and type, and management (Luo et al 2010;Sanderman et al 2010;Chan et al 2011;Powlson et al 2011). Where relatively high values (~2 Mg C ha -1 year -1…”

A review of organic carbon accumulation in soils within the agricultural context of southern New South Wales, Australia

“…no carbonate C). The annualised net rates of organic C accumulation in southern NSW have previously been reported as being very slow and often negative (Chan et al, 2011). However there were sequences of seasons where gains and losses of soil organic C were very different to the average long term trend.…”

Consistent plant residue removal causes decrease in minimum soil water content in a Mediterranean environment

“…Soil disturbance and stubble removal can each result in a loss of soil carbon (Rasmussen & Collins 1991;Dalal & Chan 2001;Chan et al 2011;Roper et al 2010Roper et al , 2013. However, there is little research that quantifies the impacts of a switch away from crop residue retention and no-till on surface residue cover and soil water content.…”