Capacity for increasing soil organic carbon stocks in dryland agricultural systems

Abstract

Abstract. Assessment of the potential for soil carbon sequestration based on soil type, land use, and climate scenarios is crucial for determining which agricultural regions can be used to help mitigate increasing atmospheric CO 2 concentrations. In semi-arid and Mediterranean-type environments, soil organic carbon (SOC) storage capacity is rarely achieved under dryland agricultural systems. We aimed to assess both actual (measured) and attainable (modelled) SOC stock values for the dryland agricultural production zone of Western Australia. We measured actual SOC storage (0-0.3 m) and known constraints to plant growth for a range of soils types (3-27% clay) and land uses (continuous cropping, mixed cropping, annual and perennial pastures) on the Albany sand plain in Western Australia (n = 261 sites), spanning a rainfall gradient of 421-747 mm. Average actual SOC stocks for land use-soil type combinations ranged from 33 to 128 t C/ha (0-0.3 m). Up to 89% of the variability in actual SOC stock was explained by soil depth, rainfall, land use, and soil type. The scenarios modelled with Roth-C predicted that attainable SOC values of 59-140 t C/ha (0-0.3 m) could be achieved within 100 years. This indicated an additional storage capacity of 5-45% (7-27 t C/ha) depending on the specific land use-soil type combination. However, actual SOC in the surface 0-0.1 m was 95 to >100% of modelled attainable SOC values, suggesting this soil depth was 'saturated'. Our findings highlight that additional SOC storage capacity in this region is limited to the subsoil below 0.1 m. This has implications for management strategies to increase SOC sequestration in dryland agricultural systems, as current practices tend to concentrate organic matter near the soil surface.

Soil carbon debt of 12,000 years of human land use

“…The rate and extent of decline in SOC stocks should vary greatly across the globe, due to differences in soil properties, climate, type of land-use conversion, and, importantly, the specific management implementation of a given form of land use. Loss of SOC under agricultural land use is not universal; modest gains are seen when soil of naturally low fertility is improved and the previous constraint (e.g., moisture, fertility, and hardpan) on plant growth is alleviated (17)(18)(19). However, for the vast majority of land, SOC loss is more common.…”

Addressing the yield gap in rainfed crops: a review

“…In higher rainfall areas (>500 mm annual rainfall) and where perennial pastures are part of the dominant farming system, soil organic matter tends to accumulate more across a range of soil types than where continuous cropping is practised (Hoyle et al 2014). In any case organic matter largely accumulates in the top 10 cm of soil in a zero tillage system such that, even if the topsoil is saturated with respect to the soil organic carbon level, the content below that depth may still below.…”

Carbon management in dryland agricultural systems. A review

“…Deep rooting can contribute to the enhancement of soil C stock in depth (Hoyle et al 2013;Jobbagy and Jackson 2000). In rainfed agriculture, the development of practices for efficient use of the whole soil profile, such as the use of species and cultivars with deeper and improved root systems, must be considered, as it is highlighted in section 2.2.…”

“…Plant biodiversity represented by polycultures, crop rotations, cover crops, and agroforestry with perennial vegetation can provide important ecosystem services (Perfecto and Vandermeer 2008. In agricultural systems, the use of that diversity in combination with other agricultural practices such as vegetative mulches, fertilization, irrigation, and the reduction of tillage intensity affects soil C pools, increasing net productivity (Hoyle et al 2013;Stockmann et al 2013).…”