Pingluo County farmland ecosystem of Ningxia in the northwest arid areas and the
Yellow River Irrigation District was selected as the research object in this study. Choose
typical sample area farmland, field investigation, sampling and laboratory analysis.
Chemical method was adapted to soil organic carbon and vegetation organic carbon. The
carbon footprint of Pingluo County was calculated based on the IPCC method and the
parameters of carbon emission. The dynamic variation and its impact factors of carbon
source and sink of Pingluo County farmland ecosystem were analyzed. The relation
between straw returning and soil organic carbon was analyzed based on the situation of
straw returning and the variation of soil organic carbon in the period from 1981 to 2010.
The main achievements of this study are listed as follows:
1. The carbon footprint of three main crops in Pingluo County was calculated based
on the investigated data of farmland production in the county by using basic theories and
research approaches of carbon footprint. The carbon footprints of corn, rice and wheat
were 931.03±142.90, 1487.56±164.59 and 809.75±144.99 kg Ce/hm 2 ·a, the carbon costs
were 0.08±0.02, 0.17±0.05 and 0.12±0.03 kg Ce/kg, respectively. The carbon footprint the
main crops in Pingluo County was exceeding the research result domestic and overseas.
Therefore, the potential of emission reduction in Pingluo County farmland ecosystem was
2. In the composition of carbon footprint of rice, corn and wheat, chemical fertilizer
carbon footprint of them were 677.94±142.09, 594.37±107.56 and 537.95±144.99 kg
Ce/hm 2 ·a, occupied 75%、40% and 66% in total carbon footprint, respectively. N fertilizer
carbon footprint of crops occupied more than 96% in chemical fertilizer carbon footprint.
Therefore, increase the use ratio of chemical fertilizer was the key to reduce the farmland
carbon footprint. 3. The carbon fixed ability of difficult crops was different. In the all kinds of crops,
the yield proportion and the carbon fixed ability of grain crops was more than economic
crops and fruits-vegetables crops. The carbon fixed ability of corn was notable especially
in grain crops. The carbon efficiency of corn (12.07±0.02 kg/kg Ce) was larger than rice
(8.49±0.03 kg/kg Ce) and wheat (5.94±0.05 kg/kg Ce), mean that the yields of corn was
the largest under the same carbon emission. So the significant way to increase the carbon
sinks of Pingluo County farmland ecosystem was appropriately expanding sown area of
4. The dynamic variation of carbon source and sink of Pingluo County farmland
ecosystem was divided into three stages during the last 10 years. The first stage was from
1991 to 1995, the amounts of carbon absorption and emission were increased. The former
was larger than the latter, so the amounts of carbon sink was increased in this stage. The
second stage was from 1996 to 2003, the amount of carbon emission was stable relatively.
The amount of carbon absorption was reduced as the reason of crop failure, so the amounts
of carbon sink was reduced slowly. The third stage was from 2004 to 2010, the amount of
carbon absorption was increased due to the cultivation of fine crops. The amount of carbon
emission was reduced slowly owing to the use of advanced agro-technology. So the
amount of carbon sink was increased substantially. The result indicated that, Pingluo
County farmland ecosystem has carbon sink function, and the ability of carbon sink was
5. The amount of crop straw land-returning of Pingluo County farmland ecosystem
was increased by degrees from 1981 to 2010. The amount of crop straw land-returning was
136.01 t/ha accumulative total, the average amount of carbon land-returning was 66.46 t/ha.
The average increased rage of soil organic carbon was 37.41%, and the increment of soil
carbon density was 6.18 t/ha. The ratio of the increment of soil carbon density and the
average amount of carbon land-returning was 9.29%. It considered that crop straw
land-returning gave the important play to carbon sink function Pingluo County farmland
Key Words: Pingluo County, farmland ecosystem, carbon footprint, crop straw