Carbon footprint of spring wheat in response to fallow frequency and soil carbon changes over 25 years on the semiarid Canadian prairie

Growing interest in environmental quality has provided a strong incentive to examine how farming practices affect agricultural products' carbon footprints (CF), an environmental quality indicator. This study determined (i) the CF of spring wheat (Triticurn aestivum L.) grown in different cropping systems over 25 years, and (ii) the effect of soil organic carbon (SOC) changes over years on wheat CF. Wheat was grown in four cropping systems: (a) fallow-wheat (FW), (b) fallow-wheat-wheat (FWW), (c) fallow-wheat-wheat-wheat-wheat-wheat (FWWWWW), and (d) continuous wheat (ContW), in replicated field plots in Saskatchewan, Canada. Wheat CF was calculated at a system level with measured variables coupled with modeling approaches. Over the 25-year period, the soil under the ContW system gained organic C of 1340 kg CO2 eq ha(-1) annually, or 38%. 55%, and 127% more than those gained in the FWWWWW, FWW, and FW systems, respectively. The SOC gain more than offset the greenhouse gas (GHG) emissions occurred during wheat production, leading to negative emission values at -742 kg CO2 eq ha(-1) annually for ContW, and -459, -404, and -191 kg CO2 eq ha(-1) for FWWWWW, FWW, and FW systems, respectively. Wheat in the ContW system produced the highest grain yield and gained highest SOC over the years, leading to the smallest (more negative) CF value at -0.441 kg CO2 eq kg(-1) of grain, significantly lower than the CF values from the three other systems (-0.102 to -0.116 kg CO2 eq kg(-1) of grain). Without considering the SOC gain in the calculation, wheat CF averaged 0.343 kg CO2 eq kg(-1) of grain and which did not differ among cropping systems. Wheat is the largest agricultural commodity in Saskatchewan, and the way the crop is produced has significant impacts on environmental quality, reflected by its carbon footprint. Cropping systems with decreased fallow frequency was shown to significantly enhance soil carbon gains over the years, increase annualized crop yields, and effectively lower the carbon footprint of this important commodity. Crown Copyright (c) 2012 Published by Elsevier B.V. All rights reserved.