Estimates Of Carbon Footprint Of Crop Production By Life Cycle Assessment (LCA) Method

Agriculture is an important greenhouse gas?GHG?emission source.Using the Life Cycle Assessment?LCA method?to evaluate GHG emissions from production and agricultural inputs and crop cultivation can identify and optimize mitigation options.This study used the LCA method to calculate the carbon footprints of major crops in different provinces of China in 2014 and in China and the United States from 2002 to 2014 based on the same system boundary.The differences in the carbon footprint of different regions in China,as well as between China and the United States and their causes were analyzed.Besides,the emission reduction potential of China's agricultural policies was also evaluated.The main conclusions are as follows:?1?There are geographical differences in the carbon footprint of China's three major food crops.The carbon footprint per yield and per area in different regions of China in 2014 were 0.37-1.40tCO₂eq·t^-1,1.18-4.32 tCO₂eq·hm^-2 for wheat;0.19-1.01 tCO₂eq·t^-1,1.38-4.79 tCO₂eq·hm^-22 for corn,and0.73-1.67 tCO₂eq·t^-1,5.58-10.46 tCO₂eq·hm^-22 for rice.The higher wheat and corn carbon footprints are generally from non-mainly cultivated areas of the crop.This is mainly due to the poor adaptability of the crops to the climatic conditions,high agricultural inputs while the output has not been significantly increased in the corresponding regions.?2?Carbon dioxide?CO₂?emissions from nitrogen fertilizer production and nitrous oxide?N₂O?emissions from farmland caused by nitrogen fertilizer application are the most important emission sources in the production of wheat and corn.CH₄ emissions in paddy fields are the most important emission source of rice production.In 2014,GHG emissions from nitrogen fertilizer production and application in 31 Provinces,municipalities,and autonomous regions accounted for41.8%-88.6%and 44.7%-84.6%of carbon footprint for wheat and corn production,repectively.CH₄emissions from rice paddies accounted for 55.5%-78.5%of carbon footprint for rice production.CO₂emissions from energy consumption of irrigation are also an important part of the crop's carbon footprint,especially in the northwest and North China.?3?The carbon footprint of wheat and corn in China is higher than that in the United States,and rice is lower than the United States.The average carbon footprint per unit of yield in China for wheat,corn,and rice production was 0.76,0.54,and 1.00 tCO₂eq·t^-1 from 2002 to 2014,while that in the United States was 0.35,0.24,and 1.24 tCO₂eq·t^-1,respectively.In China,the carbon footprint of wheat and corn production is 117.0%and 129.0%higher than that in the United States,respectively,and the carbon footprint of rice production is 20.0%lower than that in the United States.?4?Higher CO₂ emissions from nitrogen fertilizer production and N₂O emissions from nitrogen fertilizer application for wheat and corn production resulted in the higher carbon footprint in China than that in the United States.CO₂ emissions from electricity consumption for irrigation are the second contributor to the higher carbon footprints in China than that in the United State.CH₄ emissions are the main reason why the US rice carbon footprint is higher than that of China.The higher nitrogen application rate and higher energy consumptionfor fertilizer production cause large GHG emissions from nitrogen fertilizer production and application in China.China's backward irrigation technology,lower percentage of water-saving irrigation,lower irrigation water use efficiency,and less precipitation have caused China's irrigation power consumption to be much higher than in the United States.Flooded irrigation has resulted in higher methane emissions from rice paddies in the United States than in China.?5?During the period from 2002 to 2014,the GHG emissions from nitrogen fertilizer production and application for wheat and corn production in China reduced significantly?P<0.01?.CO₂ emissions from irrigation power consumption have been increasing year by year.Promotion of precision fertilization,improved fertilization techniques,and application of organic fertilizers in China induced the reduction of GHG emissions from the use of nitrogen fertilizers;Low irrigation water use efficiency,high multiple cropping index,and declining groundwater level in China have led to an increase in the annual CO₂ emissions from irrigation.?6?Carbon footprint can be further reduced through zero-growth series chemical fertilizer measures,reduction of energy consumption in fertilizer production processes,and water-saving irrigation.The carbon footprint of China's wheat,corn,and rice production in 2020 is expected to decrease by 23.0%,22.0%,and 10.0%,respectively,compared to 2014.It is estimated that the carbon footprints of wheat,corn and rice production will be reduced by 30.0%,28.0%and 12.0%respectively by 2030 compared with 2014.Identified mitigation options include:promoting soil testing formula fertilization,organic fertilizer application,no-tillage,promotion of water-saving irrigation technology andreduction of energy consumption for fertilizer production.