Strategies for reducing the carbon footprint of field crops for semiarid areas. A review
The Earth’s climate is rapidly changing largely due to increasing anthropogenic greenhouse gas (GHG) emissions. Agricultural practices during crop production, food processing, and product marketing all generate GHG, contributing to the global climate change. The general public and farmers are urging the development and adoption of effective measures to reduce GHG emissions from all agricultural activities and sectors. However, quantitative information is not available in regard to what strategies and practices should be adopted to reduce emission from agriculture and how crop productivity would affect the intensity of GHG emission. To provide the potential solution, we estimated the carbon footprint [i.e., the total amount of GHG associated with the production and distribution of a given food product expressed in carbon dioxide equivalence (CO2e)] for some of the major field crops grown on the Canadian prairie and assessed the effect of crop sequences on the carbon footprint of durum wheat. Key strategies for reducing the carbon footprint of various field crops grown in semiarid areas were identified. Carbon footprints were estimated using emissions from (1) the decomposition of crop straw and roots; (2) the manufacture of N and P fertilizers and their rates of application; (3) the production of herbicides and fungicides; and (4) miscellaneous farm field operations. Production and application of N fertilizers accounted for 57% to 65% of the total footprint, those from crop residue decomposition 16% to 30%, and the remaining portion of the footprint included CO2e from the production of P fertilizer and pesticides, and from miscellaneous field operations. Crops grown in the Brown soil zone had the lowest carbon footprint, averaging 0.46 kg CO2e kg−1 of grain, whereas crops grown in the Black soil zone had a larger average carbon footprint of 0.83 kg CO2e kg−1 of grain. The average carbon footprint for crops grown in the Dark Brown soil zone was intermediate to the other two at 0.61 kg CO2e kg−1 of grain. One kilogram of grain product emitted 0.80 kg CO2e for canola (Brassica napus L.), 0.59 for mustard (Brassica juncea L.) and flaxseed (Linum usitatissimum L.), 0.46 for spring wheat (Triticum aestivum L.), and 0.20 to 0.33 kg CO2e for chickpea (Cicer arietinum L.), dry pea (Pisum sativum L.), and lentil (Lens culinaris Medik.). Durum wheat (T. aestivum L.) preceded by an N-fixing crop (i.e., pulses) emitted total greenhouse gases of 673 kg CO2e, 20% lower than when the crop was preceded by a cereal crop. Similarly, durum wheat preceded by an oilseed emitted 744 kg CO2e, 11% lower than when preceded by a cereal. The carbon footprint for durum grown after a pulse was 0.25 kg CO2e per kg of the grain and 0.28 kg CO2e per kg of the grain when grown after an oilseed: a reduction in the carbon footprint of 24% to 32% than when grown after a cereal. The average carbon footprint can be lowered by as much as 24% for crops grown in the Black, 28% in the Dark Brown, and 37% in the Brown soil zones, through improved agronomic practices, increased N use efficiency, use of diversified cropping systems, adoption of crop cultivars with high harvest index, and the use of soil bioresources such as P-solublizers and arbuscular mycorrhizal fungi in crop production.