Effects of optimized N fertilization on greenhouse gas emission and crop production in the North China Plain

Abstract

Improving nitrogen (N) efficiency and reducing greenhouse gas (GHG) emissions are dual challenges of the agricultural sector in the North China Plain (NCP). Most relevant studies conducted in the NCP lasted only 1–2 years without sufficiently addressing the temporal variations of weather conditions and farming practices over different seasons. Thus, a 4-year (2008–2012) field experiment was conducted for a wheat–maize cropping system in a typical intensive agricultural region of the NCP. The three N application rates were (a) control without N application (CK); (b) farmers’ conventional N fertilization (CON), i.e., 600kgNha−1yr−1; and (c) optimized N fertilization (OPT), i.e., 420kgNha−1yr−1. Emissions of nitrous oxide (N2O) and methane (CH4), N uptake and crop production were measured. Compared with CON, the annual cumulative N2O emissions from OPT decreased by 40.9%, 7.2%, and 22.3% during the 2008–2009, 2009–2010 and 2011–2012 rotation years, respectively. Basal N fertilization in the wheat season was the critical period for N2O mitigation, although the maize season contributed 51%–89% of the annual N2O emission. CH4 uptake (CO2-equivalent) via soil accounted for 60%–96% of N2O in CK treatment and 4%–48% in fertilization treatments, indicating that CH4 should be considered in the overall GHG emissions from crop production. Compared with CON, OPT significantly improved N efficiency by 46%–52% for wheat and maize and maintained a similar or higher crop yield. Improvements in N efficiency should focus on the maize season. Water saving practices exhibited high potential to reduce indirect GHG emissions for the entire life cycle of crop production. Compared with CON, OPT significantly reduced the GHG intensity, particularly in the wheat season. Future long-term field experiments are required to account for considerable variations in GHG emissions and crop production under field conditions in the NCP.