Document: ING-3-59-81

Agriculture in the Great Plains: Net carbon consequences of dryland and irrigated cultivation.

BURKE, I.C.* ¹, W.K.LAUENROTH ¹, C.W.BENNETT ¹, J.BRADFORD ¹ and J.MORGAN ²

Colorado State University, Fort Collins, CO 80523 USA ¹
USDA, Fort Collins, CO 80523 USA ²

Abstract:
Historical cultivation management in the Great Plains is known to have resulted in relatively large net losses of carbon from soil organic matter. However, management practices have changed considerably over the past several decades, and it is difficult to sample changes in total soil organic matter over short time intervals. We installed Bowen Ratio towers to evaluate current annual net ecosystem production in fields representing two of the key agricultural practices of northeastern Colorado, dryland wheat-fallow and irrigated corn, in both 1998 and 1999 growing seasons. Seasonal dynamics differed strongly between the two systems, with maximum carbon capture occurring during peak leaf area index for each crop, during June for wheat and August for corn. Irrigated corn represented a relatively strong carbon sink, with a net ecosystem production of approximately 0.3 kg m^-2 per year for 1998. Dryland wheat fallow showed negative annual net ecosystem production for 1998 and 1999 at rates averaging -0.1 kg m^-2. Our data suggest that the balance of dryland and irrigated agriculture vs. native rangelands may have important consequences for regional carbon balance.

Keywords: net ecosystem production, agriculture, agroecosystem ecology, net carbon balance

This abstract is being presented at: 2:00 PM in session:
Oral Session #31: Agroecology.