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Title: No-till cropping system effects on soil profile organic carbon and total N after seven years of drought

Author
item Sherrod, Lucretia
item Ahuja, Lajpat
item HANSEN, NEIL - Colorado State University

Submitted to: Proceedings of Great Plains Soil Fertility Conference
Publication Type: Proceedings
Publication Acceptance Date: 1/15/2010
Publication Date: 3/2/2010
Citation: Sherrod, L.A., Ahuja, L.R., Hansen, N.R. 2010. No-till cropping system effects on soil profile organic carbon and total N after seven years of drought. Proceedings of Great Plains Soil Fertility Conference. p. 156-162.

Interpretive Summary: Drought has negatively impacted dryland yields in the Central Great Plains in recent years, which has a direct impact on SOC and TN levels. This study examines intensified cropping systems and their ability to maintain soil organic C (SOC) and total N (TN) levels in both surface (8 inches) and deeper soil profiles (24 inches above what has been found in wheat-fallow systems across a gradient of climates (Sterling, Stratton, and Walsh potential ET locations in Eastern Colorado averaged over soil slope position. Cropping systems included 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 systems that have been in place for 21 years were compared to a wheat-fallow (WF) system that was ended after 12 years. Comparisons to WF assume that we would continue to maintain the yields obtained over the first 12 years and that no significant erosion occurred. Although these systems have been through a 7 year drought period, cropping intensity provided increases in SOC. The trend was similar for Total N with the exception of WCF having the lowest levels in both surface and profile soils. Total N showed more sensitivity to the effects of cropping intensity than did SOC. Increased cropping intensity showed the stepwise increase for surface SOC but showed that in both profile and surface soils TN levels were significantly lower in the systems that included summer fallow (WCF and WF). In addition, WCF was found to have lower levels of TN than WF. This would suggest that the WCF system is nitrogen limited in comparison. Residue quality with the high frequency of corn in this system might also contribute to the limited N.

Technical Abstract: Intensified no-till cropping systems have been shown to increase soil organic carbon (SOC) and total N (TN) in surface soils (0-20 cm). Changes in SOC and TN are coupled to crop inputs and decomposition rates. Drought has negatively impacted dryland yields in the Central Great Plains in recent years, which has a direct impact on SOC and TN levels. This study examines intensified cropping systems and their ability to maintain SOC and TN levels in both surface (20 cm) and deeper soil profiles (60 cm) above what has been found in wheat-fallow systems across a gradient of climates and averaged over soil slope position. Cropping systems were evaluated by averaging across soils from a catenary sequence of summit, sideslope, and toeslope positions at three locations within a 420 mm precipitation zone. Sites located near Sterling, Stratton, and Walsh Colorado represents an evaporation gradient with Sterling having the lowest evaporation, and Walsh the highest. Cropping systems included wheat (Triticum sestivum)-corn (Zea mays)-fallow (WCF), continuous cropping without summer fallow (OPP) that includes wheat, corn, and millet (Panicum miliaceum) crops and a CRP grass mixture (G). These three systems that have been in place for 21 years were compared to a wheat-fallow (WF) system that was ended after 12 years. Therefore, comparisons to WF assume that we would continue to maintain the yields obtained over the 12 year period and that no significant erosion occurred. Both surface soils (0-20 cm) and profile soils (0-60 cm) were compared by ET location and across all locations for both SOC and TN. Surface soils (20 cm) showed that all systems had similar to greater SOC than WF with Stratton having the highest levels and Walsh having the lowest. Surface soil TN showed significantly higher levels in both G and OPP than what was found in both WCF and WF across all locations. Profile SOC showed that G and OPP had higher levels than WCF at Sterling but WF had higher levels than WCF. Stratton had no differences in SOC profile levels expect with G. The Walsh location had no difference in profile SOC with cropping systems including G. However this was not found when looking at profile TN values as G and OPP were significantly higher than both WF and WCF at Sterling and Stratton sites. Walsh also had a significantly higher level of profile TN in G but no difference between WF and WCF. It is of interest that at all sites the lowest level of profile TN was observed in the WCF system. Averaging across all sites, profile SOC showed no difference between cropping systems expect in G whereas in the surface soil WCF and CC had higher values than WF with G having higher levels than the annual crop systems. Profile TN averaged across sites showed even more separation by cropping systems than SOC with TN separating into 4 pools based on each cropping system (G > OPP > WF > WCF) that was observed for both surface and profile soils. This observation was not expected as we assumed that the more intensive cropping system would have similar if not higher TN values as what was found with SOC levels. In general, despite a 7 year drought period, SOC and TN levels were found to be higher in G and OPP cropping in both surface and profile soils with surface SOC showing the typical cropping intensification gradient.