Effects of nitrogen fertilizer substitution by cow manure on yield, net GHG emissions, carbon and nitrogen footprints in sweet maize farmland in the Pearl River Delta in China

Long-term excessive nitrogen (N) application in sweet maize farmland in the Pearl River Delta in China has caused huge greenhouse gas (GHG) and reactive nitrogen (RN) emissions in the region. This study compared the effects of N fertilizer replaced by cow manure at 20.00% (CD20) and 50.00% (CD50) ratios on crop yield, on-field N2O, CH4 and CO2 emissions, soil organic carbon (SOC) concentration, GHG emission intensity and carbon footprint (CF) and nitrogen footprint (NF) based on field research carried out for four consecutive cropping seasons during 2020–2021. The results showed that, compared with conventional nitrogen application (CK), CD20 could reduce N2O emissions by 6.65% and increase the SOC concentration by 48.08% when ensuring yield, although GHG emissions and intensity were both increased by 36.13%–36.44%. The CD50 lowered the crop yield 8.77% as the GHG emissions and intensity increased by 74.32%–74.58% at the same time compared to the CK, although the SOC concentration in farmland was significantly improved by 295.82% due to the higher substitution ratio of N fertilizer. Moreover, the CFs based on the area and yield of CD20 and CD50 were 23.22%–135.52% lower than CK. The NF of CD20 based on area and yield was 10.81%–16.35% lower than that of CK, but the NF of CD50 based on area and yield was 4.82%–14.90% higher than that of CK. In conclusion, replacing 20% synthetic nitrogen with cow manure in sweet maize farmland in the Pearl River Delta could achieve the synergistic technical effects of maintaining crop yield, improving the soil carbon sink and decreasing GHG and RN emissions at the life cycle level. We suggest the application of this method as an alternative fertilization practice for realizing a sustainable sweet maize cultivation system in South China. This study provided a research basis for developing the sustainable sweet maize farming system in the Pearl River Delta in China. It would also provide valuable information for the development of clean agricultural production in typical subtropical area in East Asia.