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Title: Cropping Intensity Impacts on Soil Aggregation and Carbon Sequestration in the Central Great Plains

item Mikha, Maysoon
item Benjamin, Joseph
item Vigil, Merle
item Nielsen, David

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/26/2010
Publication Date: 9/1/2010
Citation: Mikha, M.M., Benjamin, J.G., Vigil, M.F., Nielsen, D.C. 2010. Cropping Intensity Impacts on Soil Aggregation and Carbon Sequestration in the Central Great Plains. Soil Science Society of America Journal. 74(5):1712-1719. doi:10.2136/sssaj2009.0335.

Interpretive Summary: The predominant cropping system in the Central Great Plains, winter wheat-summer fallow (WF) is economically and environmentally unsustainable. This is because soil managed under WF promotes a declines in soil organic matter, is highly susceptible to wind erosion and the system has generally produced poor economic returns. Here we investigated how the quality of agricultural soil will change after 15 years of alternative cropping system management. Soil managed in a conventionally tilled WF rotation was compared to several intensive no-till (NT) rotations that varied in cropping intensity (CI) and fallow frequency. Soil parameters measured included: soil organic carbon (SOC) and total C sequestered, particulate organic matter (POM), and soil aggregate-size distribution. The crop rotation study initiated in 1990 at the USDA-ARS Central Great Plains Research Station (Akron, CO) was sampled in 2005. Soil samples were collected at 0-5 cm (surface 2 inches) and at the 5-15-cm (2-6 inches) depth from permanent grass, native prairie, and from the various crop rotations. Crops and management included in the study are winter wheat, corn, proso millet, dry pea, and summer-fallow. Rotations with no fallow and NT had greater SOC, POM and greater formation of water stable aggregates than those that had fallow and or tillage. The most intensive crop rotation (wheat-corn millet) where a crop was grown every year, increased C sequestration by 16% compared with other rotations that included fallow. Aggregate size distribution, was significantly improved by greater CI and NT. Greater amounts of macroaggregates (aggregates bigger than 0.25 mm) were associated with prairie, grass, and intensive cropping, with a corresponding shift in the proportion of micro-aggregates (aggregates smaller than 0.25 mm). Tillage elimination in the NT wheat-fallow plots improved soil POM by 24% at 0-5-cm and by 14% at 5-15-cm compared with conventional tilled wheat-fallow. Overall, a positive effect of continuous cropping and NT on soil quality as measured by macro-aggregate formation, and SOC and POM content was documented.

Technical Abstract: The predominant cropping system in the Central Great Plains is conventional tillage (CT) winter wheat–summer fallow. We investigated the effect 15 yrs of variable cropping intensity, fallow frequency, and tillage (CT and no-till [NT]) had on soil organic C (SOC) sequestration, particulate organic matter (POM), and wet aggregate-size distribution. A crop rotation study was initiated in 1990 at Akron, CO on a silt loam. In 2005, soil samples were collected from the 0- to 5- and 5- to 15-cm depths in permanent grass, native prairie, and various cropping intensities (CI) that include winter wheat (Tritucum aestivum L.), corn (Zea mays L.), proso millet (Panicum miliaceum L.), dry pea (Pisum sativum L.), and summer fallow. The native prairie provided a reference point for changes in soil parameters. The most intensive crop rotation significantly increased C sequestration compared with the other CIs where fallow occurred once every 2 or 3 yr. Legume presence in the rotation did not improve SOC sequestration relative to summer-fallow. Significant amounts of macroaggregates were associated with grass and intensive cropping compared with the rotations that included fallow. Reduced fallow frequency and continuous cropping significantly increased soil POM at 0- to 5-cm compared with NT wheat–fallow. Macroaggregates exhibited a significant positive relationship with SOC and POM. A significant negative correlation was observed between microaggregates and POM, especially at 0- to 5-cm depth. Overall, a positive effect of continuous cropping and NT was observed on macroaggregate formation and stabilization as well as SOC and POM. [GRACEnet Publication].