Potassium Fertility and Terrain Attributes in a Fragiudalf Drainage Catena
2008
Winzeler, H Edwin | Owens, Phillip R. | Joern, Brad C. | Camberato, James J. | Lee, Brad D. | Anderson, David E. | Smith, Doug R.
Site-specific management of soil fertility has been based on soil sampling in grid patterns or within soil mapping units without taking full advantage of terrain–soil relationships. The goal of this study was to determine whether terrain attributes relate significantly to soil K availability. The topographic wetness index (TWI), a terrain attribute that comprises the upstream contributing area and the slope for a portion of land, relates to soil wetness. We evaluated Mehlich-3 K (M3K), plant-available nonexchangeable K (PANK) with a modified tetraphenylboron extraction, effective cation exchange capacity (ECEC), and other soil variables from soil samples taken at three depths, and terrain attributes in a 3.6-ha farmed site in the Cincinnati catena, a major toposequence in the Muscatatuck Uplands region of Indiana. The PANK and M3K were significantly (P < 0.0001 and P < 0.05, respectively) related to TWI and relative elevation in models with anisotropic spatial autocorrelation variance estimates in three dimensions (latitude, longitude, and soil depth). The PANK and M3K increased with decreasing TWI in the following drainage class order: poorly < somewhat poorly < moderately well drained. The M3K decreased with soil depth, while PANK increased. The PANK/M3K ratio was significantly higher in the poorly drained soils than in the moderately well-drained soils, implying greater mobility or weathering of K in wetter soils. The ECEC also related strongly to terrain attributes (P < 0.0001 for relative elevation, TWI, and interaction effects). Possible mechanisms include lateral downslope lessivage and K leaching. Terrain attributes can aid in soil K fertility evaluations on the Cincinnati catena because they relate well to soil K fertility measurements.
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