Greenhouse gas emissions and global warming potential from biofuel cropping systems fertilized with mineral and organic nitrogen sources

Abstract Non-legume bioenergy crops can be fertilized with animal manures instead of mineral fertilizers, but the simultaneous application of carbon (C) and nitrogen (N) with manures can increase nitrous oxide (N2O) emissions. On the other hand, manure could increase soil organic C stocks and partly offset greenhouse gas (GHG) emissions and global warming potential (GWP) of crop systems. We performed a two-year study in a biofuel cropping system with sunflower and canola to examine the effects of manure fertilization on grain yields and N use efficiency of crops, and on GWP and GHG intensity (GHGI) in no-till soils under subtropical conditions. The GWP and GHGI were calculated from measured methane (CH4) and N2O emissions and soil organic C stock change, and from estimated carbon dioxide emissions associated with agricultural inputs and farm operations. The following treatments were tested: (i) mineral fertilizer (MF); (ii) poultry manure (PM); (iii) pig deep-litter (PDL); and (iv) no-N control. The application rate of each treatment was adjusted to provide 60 kg available N ha−1 to crops. Grain yield and N accumulated by sunflower and canola were greater in fertilized treatments than in the control, and did not differ among N sources. However, crop N use efficiency was on average 50% lower with manures than MF. CH4 emissions were not affected by N sources, but N2O emissions increased as follows: control (1.37)