Analysis On Carbon Cycle And Net Global Warming Potential For Typical Recycling Agricultural Systems

There are large quantities and many kinds of agricultural wastes in China.Most of them not only uses with low efficiency,but also caused serious greenhouse gas(GHG)emissions.At present,the comprehensive effect and impact of returning organic wastes on GHG emissions of farmland system are not unified,as well as a lack of comparative studies of GHG emissions of different agricultural recycling systems(whether recycling chain is the longer,the better?And which scale is the appropriate size?).This paper aims to systematically evaluate the net greenhouse gas warming potential(NGWP)by returning typical agricultural wastes to cropland:crop straw(CS),pig manure(PM)and biogas residue(BR).According to the life cycle perspective,NGWP of recycling system and non-recycling system are compared.Furthermore,NGWP of typical agricultural recycling systems and crop production integrated with different pig scale systems are analyzed.The main results were as follows.(1)Organic materials returning significantly increased soil GHG emission,but also increased carbon sequestration,so performance of organic material returning to the field reduced NGWP of the cropland system compared with chemical fertilizer(CF)treatment.4 year consecutive data showed that GWP of different treatments is PM>CS>BR>CF.compared with CF,CS,BR and PM improved 7.35%,49.76%and 37.54%soil carbon storage and reduced 895.66 kg C02-eq/ha/yr,3967.19 kg CO2-eq/ha/y and 3103.71 kg CO2-eq/ha/yr NGWP,respectively.BR and PM were GHG pool and had better effect of GHG reduction.GHGI in CS,BR and PM reduced 0.05-0.21 kg CO2-eq/kg grain compared with CF.(2)Crop production-pig rearing-crop production(CPC)recycling system can reduce GHG emissions compared with the non-recycling system.CPC system reduced 21.58%systematic GHG emissions firstly because it reduced 13.90%emissions from composting compared with non-recycling system.Secondly,CPC system also improved 173.38%soil carbon sequestration compared with non-recycling system,which effectively counteracted GHG emissions from PM returning.Thirdly,compared with non-recycling system,CPC system reduced 43.48%emissions avoided from the use of chemical fertilizer.Furthermore,through transportation CPC system reduced GHG emissions achieve to 120.95kg C02-eq/yr.(3)Compared with CC(crop production-crop production)system,CPC and CPBC(crop production-pig rearing-biogas production-crop production)system had a lower NGWP,and with the extension of the recycling chain,the effect of emission reduction was better.CPC and CPBC system reduced 14.83%and 354.06%NGWP compared with CC system.On the one hand,the reason is that returning organic materials in CPC and CPBC system can increase 76.01%and 88.19%soil carbon pool.On the other hand,in the process of pig rearing,CPC system reduced 5.27%emissions by fertilizer utilization and CPBC system reduced 5.27%emissions by energy utilization.(4)With the expansion of pig rearing scale,the NGWP performance of crop production integrated with different pig scale systems are better.The NGWP order from different pig rearing modes was thousand>one hundred thousand>hundred>farmer’s scattered breeding.After the system formed a circulatory system,compared with non-integrated system,the emissions of farmer’s scattered breeding,hundred,thousand and one hundred thousand modes were reduced by 3.01%,4.97%,4.77%and 5.28%,respectively.In actual production system,NGWP of farmer’s scattered breeding,hundred,thousand and one hundred thousand modes decreased by 10.31%,5.84%,4.77%and 16.76%,respectively.In conclusion,Organic materials returning reduced NGWP of the cropland system compared with CF treatment.CPC system can reduce GHG emissions compared with the non-recycling system.With the extension of the recycling chain,the effect of GHG reduction in CC system,CPC system and CPBC system were better.With the expansion of pig rearing scale,the NGWP performance of crop production integrated with different pig scale systems are better.