Effect of long-term fertilization on greenhouse gas emissions and carbon footprints in northwest China: A field scale investigation using wheat-maize-fallow rotation cycles

Improving agriculture intensity implies desirable crop productivity at a noteworthy environmental cost. A comprehensive comparative analysis of carbon footprint (CF) and greenhouse gases emissions (GHGs) of the two major and contrasting cropping systems is of paramount importance, which is rarely done. The life-cycle assessment (LCA) was performed to assess the alleviating potential, and differences in CF of wheat and maize crops within irrigated and rain-fed cropping systems. The two 25-year experiments included a winter wheat-summer maize cropping under irrigated conditions with five treatments: Control without fertilization (CK), combination of nitrogen and phosphorus (NP), NP plus potassium (NPK), NPK plus crop straw (S) (SNPK), and dairy manure (M) integrated with NPK (MNPK); and a winter wheat-summer fallow system under rain-fed conditions with four treatments as stated above except SNPK. Results showed that high N input increased total GHG emission and CF across cropping systems in question. The mean GHGs’ emissions ranged from 2000.9 to 7586.7 kg ha−1 for irrigated cropping system, and 192.5–1834.6 kg ha−1 for rain-fed cropping system. Over the 25 years, without considering SOC gain, the mean CF values for irrigated and rainfed cropping systems ranged from 0.51 to 0.62 and 0.16–0.50 kg CO2 kg−1 of grain, respectively. When SOC gains were involved in, the mean CF values for the two investigated cropping systems ranged from 0.22 to 0.42 and −0.26 to 0.29 kg CO2 kg−1 of grain, respectively (in exclusion of SNPK). SOC sequestration played an important part in reduction of CF. Our research may provide valuable information to promote the optimization of agricultural practices and guide the design/choice of future farming systems in the region and where with similar environmental conditions.