Progress 12/05/14 to 09/30/16
Outputs
Target Audience: Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?The undergratuate and graduate students have become familiar with soil carbon cycling. How have the results been disseminated to communities of interest?The results were shared with growers in Alabama and through the annual Certified Crop Advisors training. What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
Soil Carbon in Alabama Blackland Prairie Vertisols Acid and alkaline soils (mostly Vertisols) exist in close proximity in the Alabama Blackland Prairie region. Besides higher pH's in the upper portions of the solum, alkaline soils contain higher quantities of inorganic carbon. Upland soil disparities in this region are likely due to differences in weathering, changes in parent material and/or the presence of lithologic discontinuities, or both. Identifying soil parent materials is fundamental to pedogenic study, survey, and interpretation, and is a basis for understanding soil carbon sequestration in this region. The objective of the first part of this investigation was the evaluation of parent material uniformity for improved understanding of Alabama Blackland Prairie pedogenesis. Alkaline (Sumter- Rendollic Eutrudept and Okolona- Oxyaquic Hapludert) and acid (Vaiden- Aquic Dystrudert and Oktibbeha- Chromic Dystrudert) soils were sampled to chalk (eight pedons total). Particle size analysis and fractionation was utilized to isolate fractions for mineralogical and elemental analyses. Fractions were digested, and concentrations of Sr, Ti, Y, Zr were measured. Calcium carbonate (CaCO3) was quantified using thermogravimetric analyses (TGA), and clay separates were analyzed using X-ray diffraction (XRD). Uniformity values and the aggregate of data suggests that parent materials are relatively uniform in these alkaline soils, but vary with depth in acid soils, indicating a polygenetic formation pathway for these acid soils. Pedogenic inorganic carbonates are a critical part of the global carbon cycle. Pedogenic carbonates form mostly under drier climates, however, carbonates in Alabama Blackland Prairie region soils (mostly Vertisols) possess pedogenic morphology. The characterization of inorganic carbonates in these environments increase our understanding of soil C cycling. Inorganic carbonates (soft and cemented masses) from two soils of this region (Rendollic Eutrudept and Oxyaquic Hapludert) were characterized and quantified. Suspected pedogenic and lithogenic carbonate forms were characterized using several approaches. Calcium carbonate quantities ranged from 8 to 43% and 52 to 62% in the Hapludert and Eutrudept, respectively. Significant differences (p ≤ 0.05) in the mean isotopic C values of soft masses, nodules, and lithogenic (rock) carbonate forms existed. Differences were also found between light rare earth element concentrations of suspected pedogenic and lithogenic carbonate forms, although heavy rare earth elemental concentrations did not differ. Multiple lines of evidence indicate significant pedogenic carbonates exist in these Blackland Prairie soils.
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Progress 12/05/14 to 09/30/15
Outputs
Target Audience:My Target audience were other soil scientist. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?
Nothing Reported
How have the results been disseminated to communities of interest?
Nothing Reported
What do you plan to do during the next reporting period to accomplish the goals?Research in 2016 will explore carbon (C) cycling in Alabama Blackland Prairie soils. These clayey soils have unique soil formation pathways and contain both pedogenic and lithogenic inorganic carbonate forms, Soil carbonates in these soils are a significant terrestrial C pool that has received relatively little study. Thus, an objective of this project is to evaluate origins of inorganic carbonates in these soils to obtain a better understanding of C cycling in these humid, southeastern U.S. landscapes.
Impacts
What was accomplished under these goals?
Soil organic matter (SOM) is the key indicator of soil quality in highly weathered southeastern U.S. agronomic systems. The Old Rotation research site was established in 1896 on the campus of Auburn University, and is the oldest continuous cotton (Gossypium hirsutum) experiment in the world. The experiment includes 13 plots with differing crop rotation, fertility, and cover crop treatments. In 2003, irrigation was added as an additional treatment by splitting plots into irrigated and non-irrigated subplots. The Old Rotation was selected as a research site because of the unique opportunity to study long-term effects of crop rotations, cover crops and irrigation on SOM content. In 2015, two transects were placed through the experimental site; one through the irrigated and one through the non-irrigated section. Each transect covered all 13 plots with three measurements in each plot. Soil samples were collected from the top 15 cm, and SOM was measured by loss on ignition (LOI). Volumetric water content (θv) was measured using time domain reflectometry (TDR) on three different dates. TDR measurements were replicated at three locations to account for local-scale soil spatial variability. Both cover crops and irrigation significantly affected SOM content at the 0.01 and 0.05 levels, respectively. The SOM content in plots with and without cover crops was 4.4 ±0.8% and 3.3 ±1.5%, respectively. Thus, cover crops increased the SOM content relatively by 33%. The SOM content of irrigated and non-irrigated treatments was 4.2 ±1.1% and 3.7 ±1.3%, respectively. Thus, irrigation over the last 12 years increased SOM by 13%. The volumetric water content was measured on January 22, March 17, and April 27, 2015. Plots with cover crops had higher average volumetric water contents for each date (15.6, 15.6, 16.4% for measurements in January, March, and April, respectively) in comparison to plots without cover crops (11.9, 12.1, and 11.8% for January, March, and April, respectively). ANOVA was used to assess effects of cover crop, irrigation, and date on volumetric water content with cover crop and irrigation being significant at an alpha level of 0.01 but date having no significant effect on volumetric water content. Cover crop and irrigation increased the volumetric water content. Irrigated plots, however, were not actually irrigated during the time of study. Higher volumetric water content for the plot with cover crops and irrigation could be explained by less evaporation from the soil surface because of the cover crop layer. Higher amounts of soil organic matter also contribute to more water retention and therefore higher volumetric water contents.
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