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Title: MANAGEMENT EFFECTS ON CLAY DISPERSIBILITY OF A RHODIC PALEUDULT IN THE TENNESSEE VALLEY REGION, ALABAMA

Author
item SHAW, J - AUBURN UNIVERSITY
item Reeves, Donald
item Truman, Clinton
item MITCHELL, P - AUBURN UNIVERSITY

Submitted to: Southern Conservation Tillage for Sustainable Agriculture Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 6/24/2002
Publication Date: 6/24/2002
Citation: Shaw, J.N., Reeves, D.W., Truman, C.C., Mitchell, P.A. 2002. Management effects on clay dispersibility of a rhodic paleudult in the tennessee valley region, alabama. In: Van Santen, E., editor. Proceedings of the 25th Annual Southern Conservation Tillage Conference for Sustainable Agriculture - Making Conservation tillage Conventional: Building a Future on 25 Years of Research. Special Report no. 1, Alabama Agricultural Experiment Station and Auburn University, June 24-26, Auburn, Alabama. p. 201-206.

Interpretive Summary: Historically, conventional tillage coupled with cotton monoculture has resulted in soil degradation in the Tennessee Valley Region but conservation tillage systems that improve soil quality are increasingly being used by producers. The surface soil layers in the region have appreciable amounts of silt and clay. These fine particles can disperse under rainfall, reducing soil tilth and degrading soil physical properties. We evaluated the clay dispersibility of these soils cropped to cotton in: 1) a no-till system without a cover crop, 2) a no-till system with a rye cover crop, 3) a no-till system with a rye cover crop and fall paratilling, and 4) a conventional tillage system. Increased soil carbon under conservation tillage systems increased water dispersible clay quantities. Chemicals called iron oxides were more important to reducing clay dispersibility and improving physical properties in the surface of this silt loam soil than soil carbon or organic matter. This information can be used by scientists and NRCS specialists to refine conservation systems for the region that further increase infiltration and improve cotton yields, while improving soil quality.

Technical Abstract: Conventional tillage coupled with monoculture cotton (Gossypium hirsutum L.) production has resulted in declining soil quality in the Tennessee Valley Region. However, conservation tillage systems that have been shown to increase soil quality are increasingly more common. Surface horizons in the region have appreciable silt and clay, which are mostly composed of quartz, kaolinite, hydroxy-interlayered vermiculite, and Fe oxides. Similar clay mineralogical suites have been shown to be dispersive under certain conditions, which can degrade soil physical properties. We evaluated the clay dispersibility of these soils cropped to cotton in: 1) a no-till system without a cover crop (NT), 2) a no-till system with a rye (Secale cereale L.) cover crop (NTC), 3) a no-till system with a rye cover crop and fall paratilling (NTCP), and 4) a conventional tillage system (CT). Soils consisted of fine, kaolinitic, thermic Rhodic Paleudults. Water dispersible clay (WDC), extractable Fe forms, and soil organic carbon (SOC) were evaluated for surface samples. Particle size distribution (PSD) and mineralogy of in situ soil, runoff sediment, and WDC were also evaluated. Increased clay amounts were recovered when samples had dithionite extractable Fe removed (Fed) compared to soil organic matter removal. The WDC quantities were positively correlated with SOC (%), which was higher under reduced versus conventional management, and negatively correlated with Fed (%) and water stable aggregates (%). The aggregate of data suggests Fe oxides play a more vital role in clay aggregation than SOC in these soil systems. Particle size and mineralogy of runoff sediment collected under simulated rainfall was similar to in situ soil, suggesting models depicting erosion and nutrient runoff can be developed using in situ soil as a surrogate for sediment characterization.