ARS | Publication request: SOIL ORGANIC CARBON POOL CHANGES UNDER LONG-TERM NO-TILL AND CROPPING INTENSITY REGIMES ACROSS AN EVAPOTRANSPIRATION GRADIENT IN EASTERN COLORADO, USA

Submitted to: International Soil Tillage Research Organization Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: July 13, 2006
Publication Date: September 2, 2006
Citation: Ma, L., Sherrod, L.A., Peterson, G., Hansen, N., Ahuja, L.R. 2006. Soil organic carbon pool changes under long-term no-till and cropping intensity regimes across an evapotranspiration gradient in Eastern Colorado, USA. International Soil Tillage Research Organization Proceedings. KIel, Germany. 8/28 - 9/3/2006. (Abstract)

Interpretive Summary: Increasing precipitation use efficiency and soil quality is essential for the sustainability of dryland agriculture. A long-term study was initiated in 1985 at Sterling, Stratton, and Walsh in Eastern Colorado with increasing potential evapotranspiration (PET) demand. Each location had a catena consisting of summit, sideslope, and toeslope soil positions and crop rotations of wheat-fallow (WF), wheat-maize (corn)-fallow (WCF), wheat-maize (corn)-prosomillet-fallow (WCMF), and continuous cropping (CC) without summer fallow. Soil organic carbon (SOC) and total soil nitrogen (TSN) in the 10 cm soil profile after 12 years of cultivation increased with increasing cropping intensity. Increases in SOC were greater under lower PET than under higher PET, and were higher at toeslope than at summit and sideslope soil positions. Increases in SOC occurred primarily because of increases in the slow C pools (particulate organic matter C, POMC). The active (mineralized C during a 3-day incubation) and the stable soil C-pool (mineral associated organic C, MAOC) decreased in most crop rotations during the 12-year experimental period. The observed changes in SOC pools are to compare with model-simulated changes and to be used as a basis for SOC modeling in agricultural system models.

Technical Abstract: Increasing precipitation use efficiency and soil quality is essential for the sustainability of dryland agriculture. A long-term study was initiated in 1985 at three sites in Eastern Colorado which represent a potential evapotranspiration (PET) gradient of 1000, 1400, and 1900 mm of open pan evaporation. Each location had a catena consisting of summit, sideslope, and toeslope soil positions and crop rotations of wheat-fallow (WF), wheat-maize(corn)-fallow (WCF), wheat-maize(corn)-prosomillet-fallow (WCMF), and continuous cropping (CC) without summer fallow. Soil organic carbon (SOC) and total soil nitrogen (TN) in the 10 cm soil profile increased with increasing cropping intensity. Increases in SOC were greater under lower PET than under higher PET, and were higher at toeslope than at summit and sideslope soil positions. Increases in SOC occurred primarily because of increases in the slow C pools (particulate organic matter C, POMC). The active (mineralized C during a 3-day incubation) and the stable soil C-pool (mineral associated organic C, MAOC) decreased in most crop rotations during the 12-year experimental period. The Root Zone Water Quality Model (RZWQM) will be used to simulate the effect of crop rotation and PET/soil on SOC dynamics. Emphasis will be placed on comparing simulated soil organic C pools to the measured active, slow, and stable C pools under different cropping systems.