Assessment Of Carbon,Nitrogen Footprints And Economic Benefits On Different Cultivation

As a light and simplified planting method,ratooning rice has been widely advocated,but the best cultivation mode has not been unified yet.In recent years,researchers have mostly studied the changes of physiological morphology and yield of ratooning rice from the perspective of monoculture,but have not integrated an optimal model to comprehensively analyze its economic benefits and impact on the environment.Therefore,field experiments were carried out in Lanjie Village,Huaqiao Town,Hubei Province in 2020-2021.Two conventional cultivation modes were set up:CK1（winter fallow+artificial seedling transplanting+balanced fertilization+conventional irrigation+20 cm stubble+straw returning in the first season）and CK2（winter fallow+mechanical seedling transplanting+balanced fertilization+conventional irrigation+20 cm stubble+straw returning in the first season）,and three optimal cultivation modes were as follows:OM1（winter fallow+mechanized seedling transplanting+one-time slow release fertilizer application+dry-wet alternation+20 cm stubble+first season straw return）,OM2（green fertilizer+mechanized seedling transplanting+balanced fertilization+40 cm stubble+first season straw return）,OM3（green fertilizer+mechanized seedling transplanting+balanced fertilization+base fertilizer deep application+dry-wet alternation+40 cm stubble+return of first season straw plus decomposing agent）.The effects of different cultivation modes on greenhouse gas emissions,yield and economic benefits of ratooning rice were studied,and carbon and nitrogen footprints of different cultivation modes were evaluated.The results are as follows:（1）Cultivation patterns significantly affected methane（CH₄）emissions.CH₄ emission in rice season was higher than that in winter,and in the first season was higher than that in regeneration season.CH₄ emission occurred at tiller stage of the first season,heading stage and heading stage of the regeneration season.Compared with OM2,OM1,CK2 and CK1,THE cumulative emissions of OM3 in the first quarter were 21.3%,42.4%,44.8%and 52.6%,respectively.Compared with OM2,OM1,CK2 and CK1,the cumulative annual emissions of OM3 decreased by 13.0%,26.3%,38.3%and 43.5%,respectively.Nitrous oxide（N₂O）emissions showed a peak after each fertilization.The cumulative N₂O emissions of OM2 and OM3N₂O in winter were significantly higher than those of OM1 and CK2,increasing by 39.7%-52.9%and 65.0%-78.9%,respectively.（2）Cultivation patterns significantly affect economic benefit and net ecosystem economic benefit（NEEB）.OM3 had the highest economic efficiency(21046 CNY ha^-1),which was 1.05,1.27,1.28,1.36 times of OM2,OM1,CK2 and CK1.The NEEB of OM3 and OM2 was significantly higher than that of OM1,CK2 and CK1,and OM1 was the highest(20768 CNY ha^-1),which was 1.05,1.28,1.26 and 1.38 times of OM2,OM1,CK2 and CK1.（3）Cultivation patterns significantly affect carbon footprint.The annual carbon emission of each model is 9246～11329 kg ha^-1.In terms of the composition of total carbon emissions,CH₄ emissions accounted for 56.7%-76.1%of the total emissions.The second was agricultural inputs（indirect emissions）,accounting for 14.3-26.1%of total emissions.Fertilizer was the largest contributor to indirect emissions,accounting for 52.4%-60.2%of indirect emissions.N₂O emission is the lowest,accounting for 7.5%-15.2%of the total emissions.The mean carbon footprints of CK1,CK2,OM1,OM2 and OM3 were 0.95,0.89,0.75,0.64 and 0.57 kg CO₂-eq kg^-1 year^-1,respectively.The carbon footprints of OM3 and OM2 were significantly lower than those of other models.（4）Cultivation pattern significantly affected nitrogen footprint.The active nitrogen loss of each mode ranged from 36398.1 to 43784.7 g N-eq ha^-1.Ammonia（NH₃）volatilization is the main source of reactive nitrogen loss,accounting for about 82%.The annual total NH3volatilization of CK1,CK2,OM1,OM2 and OM3 were 29.94,30.87,31.22,33.85 and 35.49kg ha^-1,respectively,and the NH₃ volatilization of OM3 was significantly higher than that of OM1,CK2 and CK1.The nitrogen footprints of CK1,CK2,OM1,OM2 and OM3 ranged from2.82 to 3.12 g N-eq kg^-1 year^-1,among which OM1 had the smallest nitrogen footprint and CK1had the largest nitrogen footprint.（5）The cultivation pattern significantly affected the yield of first rice and ratooning rice.The yield in the first season,the regeneration season and the whole growth period was higher in the optimized cultivation mode than in the conventional cultivation mode.For the first season,the yield of OM1,OM2 and OM3 was significantly higher than that of CK1 and CK2,increasing by 7.66%to 15.2%.For regenerating season,the yield of OM2 and OM3 was significantly higher than CK1,CK2 and OM1,increasing by 28.1%-44.2%.For the whole growth period,the yield of OM2 and OM3 was significantly higher than that of CK1,CK2 and OM1,with an increase range of 12.5%-25.9%.In conclusion,compared with other modes,OM3 reduces CH₄ emissions and carbon footprint,improves the yield and NEEB of ratooning rice,and maintains a low nitrogen footprint.Therefore,it is a cultivation mode of ratooning rice with low emission,high yield and high economic benefits,which is expected to be widely implemented.