Carbon balance of an intensively grazed temperate pasture in two climatically contrasting years

► The carbon balance of an intensively grazed pasture was measured for 2 years. ► There was a severe drought during the 1st year, and the 2nd year was very cold. ► During the drought period there was a large loss of CO 2 to the atmosphere. ► Despite the climatic extremes the site was a small C sink...

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Published in:Agriculture, ecosystems & environment ecosystems & environment, 2011-11, Vol.144 (1), p.271-280
Main Authors: Mudge, P.L., Wallace, D.F., Rutledge, S., Campbell, D.I., Schipper, L.A., Hosking, C.L.
Format: Article
Language:English
Subjects:
Agronomy. Soil science and plant productions
Animal productions
atmosphere
Autumn
Biological and medical sciences
biomass
Carbon
Carbon budget
Carbon dioxide
carbon sequestration
carbon sinks
dairies
Dairy farm
drought
Droughts
Ecosystems
Eddy covariance
farms
feeds
Fundamental and applied biological sciences. Psychology
General agroecology
General agroecology. Agricultural and farming systems. Agricultural development. Rural area planning. Landscaping
General agronomy. Plant production
Generalities. Agricultural and farming systems. Agricultural development
Grassland
grasslands
ice
Imports
International trade
land use
leaching
methane
milk
mineral soils
net ecosystem exchange
pastures
rain
Soil carbon
soil water
Soils
spring
summer
temperature
Terrestrial animal productions
Vertebrates
winter
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Summary:► The carbon balance of an intensively grazed pasture was measured for 2 years. ► There was a severe drought during the 1st year, and the 2nd year was very cold. ► During the drought period there was a large loss of CO 2 to the atmosphere. ► Despite the climatic extremes the site was a small C sink in both years. ► The net ecosystem carbon balance was 590 kg ha −1 in 2008 and 900 kg ha −1 in 2009. Grazed grasslands occupy 26% of the earth's ice free land surface and are therefore an important component of the global C balance. In New Zealand, pastoral agriculture is the dominant land use and recent research has shown that soils under intensive dairy pastures have lost large amounts of carbon (∼1000 kg C ha −1 y −1) during the past few decades. The objective of this research was to determine the net ecosystem carbon balance (NECB) of an intensively grazed dairy pasture in New Zealand. Net ecosystem CO 2 exchange (NEE) was measured using an eddy covariance (EC) system from 1 January 2008 to 31 December 2009. Other C imports (feed) and exports (milk, methane, leaching, and harvested biomass) were calculated from farm production data and literature values. During 2008 there was a one in 100 year drought during summer/autumn, which was followed by a very wet winter. There were no prolonged periods of above or below average rainfall or soil moisture in 2009, but temperatures were consistently lower than 2008. The severe summer/autumn drought during 2008 caused a loss of CO 2 to the atmosphere, but annual NEE remained negative (a CO 2 sink, −1610 ± 500 kg C ha −1), because CO 2 lost during the drought was regained during the winter and spring. The site was also a net CO 2 sink during 2009 despite the colder than usual conditions (−2290 ± 500 kg C ha −1). Including C imports and exports in addition to CO 2 exchange revealed that the site was a C sink in both years, with a NECB of 590 ± 560 kg C ha −1 in 2008, and 900 ± 560 kg C ha −1 in 2009. The C sequestration found in this study is in agreement with most other Northern Hemisphere EC studies of grazed pastures on mineral soils, but is not consistent with the large C losses reported for soils under dairy pastures throughout New Zealand. In the current study (like many other EC studies) the influence of climatic conditions and management practices on the annual C balance was only semi-quantitatively assessed. An extended period of EC measurements combined with modelling is required to more accurately quantify the
ISSN:0167-8809
1873-2305
DOI:10.1016/j.agee.2011.09.003