World crop residues production and implications of its use as a biofuel

Reducing and off-setting anthropogenic emissions of CO2 and other greenhouse gases (GHGs) are important strategies of mitigating the greenhouse effect. Thus, the need for developing carbon (C) neutral and renewable sources of energy is more than ever before. Use of crop residue as a possible source of feedstock for bioenergy production must be critically and objectively assessed because of its positive impact on soil C sequestration, soil quality maintenance and ecosystem functions. The amount of crop residue produced in the US is estimated at 367×106 Mg/year for 9 cereal crops, 450×106 Mg/year for 14 cereals and legumes, and 488×106 Mg/year for 21 crops. The amount of crop residue produced in the world is estimated at 2802×106 Mg/year for cereal crops, 3107×106 Mg/year for 17 cereals and legumes, and 3758×106 Mg/year for 27 food crops. The fuel value of the total annual residue produced is estimated at 1.5×1015 kcal, about 1 billion barrels (bbl) of diesel equivalent, or about 8 quads for the US; and 11.3×1015 kcal, about 7.5 billion bbl of diesel or 60 quads for the world. However, even a partial removal (30-40%) of crop residue from land can exacerbate soil erosion hazard, deplete the SOC pool, accentuate emission of CO2 and other GHGs from soil to the atmosphere, and exacerbate the risks of global climate change. Therefore, establishing bioenergy plantations of site-specific species with potential of producing 10-15 Mg biomass/year is an option that needs to be considered. This option will require 40-60 million hectares of land in the US and about 250 million hectares worldwide to establish bioenergy plantations.