Drought and Cropping Intensity Impact On Soil Organic Carbon and Total N Across A Catena Sequence.

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.