Drought and cropping intensity impact on soil organic carbon and total N across a cantena sequence

Authors: Sherrod, Lucretia; Ahuja, Lajpat; HANSEN, NEIL - Colorado State University; PETERSON, GARY - Colorado State University; WESTFALL, DWAYNE - Colorado State University

Submitted to: ASA-CSSA-SSSA Annual Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 9/27/2010
Publication Date: 11/2/2010
Citation: Sherrod, L.A., Ahuja, L.R., Hansen, N., Peterson, G.A., Westfall, D. 2010. Drought and cropping intensity impact on soil organic carbon and total N across a cantena sequence. ASA-CSSA-SSSA Annual Meeting Abstracts. Paper No. 61344.

Interpretive Summary: The Central Great Plains in recent years has gone through a serious drought which can have a direct impact on soil organic matter. Cropping intensity or frequency of fallow has a direct impact on soil organic matter levels because the crop residues returned to the soil decompose into soil organic matter. This study compares the current levels of soil organic C and total N in intensified cropping systems and grass systems to a depth of 20 cm to what has been found in the traditional wheat-fallow (WF) system in dryland production across a range of ET at 3 locations in Eastern Colorado and 3 landscape positions within the locations. Cropping systems include wheat-corn-fallow (WCF), continuous cropping without summer fallow (OPP) that includes wheat, corn, and millet crops, and a conservation reserve program (CRP) of native grass mixture of warm and cool season species (G). These 3 no-till systems that have been in place for 21 years were compared to no-till WF that was ended 9 years previous. Comparisons to WF assume that we would continue to maintain similar yields obtained over the first 12 years of the study and that no significant erosion occurred. Although these systems have been through a 7 year drought period, cropping intensity provided increases in SOC in most of the site and slope positions relative to WF. Cropping intensification showed similar to markedly higher SOC levels in 70% of the site by slope by cropping system comparisons. Cropping intensification showed similar to markedly higher total N levels in 92% of the site by slope by cropping system comparisons. The toeslope soils showed the most dramatic differences in SOC and total N levels from the WF levels found in 1997. Total N showed more sensitivity to the effects of cropping intensity than did SOC.

Technical Abstract: Drought has negatively impacted dryland yields in the Central Great Plains in recent years, which has a direct impact on SOC levels. This study examines intensified cropping systems and their ability to maintain soil organic C (SOC) and total N in the 0-20 cm above what has been found in wheat-fallow systems across a gradient of climates (potential ET locations in Eastern Colorado) and across summit, side and toeslope landscape positions. Cropping systems include wheat-corn-fallow (WCF), continuous cropping without summer fallow (OPP) that includes wheat, corn, and millet crops, and a CRP grass mixture (G). These three no-till systems that have been in place for 21 years were compared to a no-till wheat-fallow (WF) system that was ended 9 years previous. Comparisons to WF assume that we would continue to maintain similar yields obtained over the first 12 years of above average precipitation and that no significant erosion occurred. If our yield assumptions of uniformity are incorrect then the SOC and TN results would be even more dramatic in favor of more intensive cropping systems. Although these systems have been through a 7 year drought period, cropping intensity provided increases in SOC in most of the site and slope positions relative to WF. The highest SOC levels were found in G in 7 out of the 9 soils. The trend was similar for Total N. These results show that reducing fallow frequency by increasing cropping intensity, SOC and TN levels can increase but not to the level achieved with the perennial grasses.