CARBON LIFE CYCLE ASSESSMENT FOR PRAIRIE AS A CROP IN RECLAIMED MINE LAND

A life cycle assessment with carbon (C) as the reference unit was used to balance the benefits of land preparation practices of establishing tall-grass prairies as a crop for reclaimed mine land with reduced environmental damage. Land preparation and management practices included disking with sub-soiling (DK-S), disking only (DK), no tillage (NT), and no tillage with grazing (NT-G). To evaluate the C balance and energy use of each of the land preparations, an index of sustainability (I-s=C-O/C-I, Where: CO is the sum of all outputs and C-I is the sum of all inputs) was used to assess temporal changes in C. Of the four land preparation and management practices, DK had the highest I-s at 8.53. This was due to it having the least degradation of soil organic carbon (SOC) during land-use change (-730 kg ha(-1) y(-1)) and second highest aboveground biomass production (9,881 kg ha(-1)). The highest aboveground biomass production occurred with NT (11,130 kg ha(-1)), although SOC losses were similar to DK-S, which on average was 2,899 kg ha(-1) y(-1). The I-s values for NT and DK-S were 2.50 and 1.44, respectively. Grazing from bison reduced the aboveground biomass to 8,971 kg ha(-1) compared with NT with no grazing, although stocking density was low enough that I-s was still 1.94. This study has shown that converting from cool-season forage grasses to tall-grass prairie results in a significant net sink for atmospheric CO2 3 years after establishment in reclaimed mine land, because of high biomass yields compensating for SOC losses from land-use change. Copyright (C) 2014 John Wiley & Sons, Ltd.