Biochar combined with N fertilization and straw return in wheat-maize agroecosystem: Key practices to enhance crop yields and minimize carbon and nitrogen footprints

Straw incorporation is widely applied to improve crop productivity, and biochar amendment may be an effective countermeasure for mitigating greenhouse gas (GHG) emissions; however, the comprehensive evaluation of straw return and biochar amendment coupled with different N application rates on soil organic carbon (SOC) sequestration rate, GHG emissions, and reactive N losses have been inadequately recorded. Consequently, the field experiment had six treatments and three replications including two mineral N fertilization rates (conventional N fertilizer application (N1) and 30% reduced N fertilizer application (N0.7)) and three types of straw and biochar management variations (no straw incorporation (S0), straw incorporation (S), and straw incorporation with biochar amendment (SB)) and the results were based on three years of soil SOC and GHGs emission data in wheat-maize agroecosystem. Our finding revealed that N0.7 reduced the GHG emissions (CO2: 13.9%; N2O: 34.2%; CH4: 32.5%), greenhouse gas intensity (GHGI; 32.7%), carbon footprint (CF; 35.1%) and nitrogen footprint (NF; 24.5%), but had no significantly different crop yields compared with N1 (p > 0.05). Straw incorporation had no significant impact on CF and yield-scaled CF but increased NF (29.7%) because the stimulated GHG emissions would be offset by SOC sequestration. Under S, the wheat and maize yields increased by 9.7% and 5.4%, respectively, whereas the GHGI increased by 59.6% compared with S0. Biochar amendment reduced GHG emissions (CO2: 19.9%; N2O: 29.9%), GHGI (32.7%), CF (26.7%) and yield-scaled CF (29.2%), while improving crop yields (wheat: 5.8% (p < 0.05); maize: 1.5% (p > 0.05)) and SOC sequestration rate (74.5%) compared with that under S. Overall, N0.7SB exhibited enormous potential for enhancing wheat-maize agroecosystem productivity and drastically mitigating their CF and NF in the semi-arid conditions of the Guanzhong Plain.