Bio-mitigation of carbon following afforestation of abandoned salinized farmland

As the global demand for food continues to increase, the displacement of food production by using agricultural land for carbon mitigation, via either carbon sequestration, bioenergy or biofuel is a concern. An alternative approach is to target abandoned salinized farmland for mitigation purposes. Australia, for example, has 17 million ha of farmland that is already or could become saline. At a representative, salinized, low rainfall (350mmyr-1) site at Wickepin, Western Australia, we demonstrate that afforestation can mitigate carbon emissions through either providing a feedstock for bioenergy or second generation biofuel production and produce salt-tolerant fodder for livestock. A range of factors markedly affect this mitigation. These include hydrological conditions such as salinity, site factors such as slope position and soil properties and a range of silvicultural factors such as species, planting density and age of the planting. High density (2000stemsha-1) plantings of Eucalyptus occidentalis Endl. produced a mean total biomass of 4.6tha-1yr-1 (8.5t CO2-e ha-1yr-1) averaged over 8years. Atriplex nummularia Lindl. produced a mean total biomass of 3.8tha-1yr-1 (6.9t CO2-e ha-1yr-1) averaged over 4years and approximately 1.9tha-1yr-1 of edible dry matter annually to 8years of age. With differences in salt tolerance between E. occidentalis and A. nummularia, we propose an integrated approach to treating salinized sites that takes salinity gradients into account, replicates natural wetland ecosystems and produces both fodder and biomass. Continued mitigation is expected as the stands mature, assuming that growth is not affected by the accumulation of salt in the soil profile. Such carbon mitigation could potentially be applied to salinized farmland globally, and this could thus represent a major contribution to global carbon mitigation without competing with food production.