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Fluid Journal : Fluid Journal 2005-2007
to additional K (Figure 1), confirming that K is an important factor contributing to the slow early season growth and lower grain yield from the reduced-till plots at the Ames, Iowa, research site. Bio-available K Measurements of bio-available K with resin sheets were successful. Higher concentrations of K were measured near the soil surface for all three of the K placements three weeks after application (Figure 2). Similar results were recorded six weeks after application (data not shown). The highest concentration of bioavailable K was found at a depth of one to two inches below the surface for the 0-0-30 dribble treatments; however, higher concentrations of K also were measured throughout the one- to two-inch soil layer after broadcast application of 0-0-30 (Figure 2). In contrast, only small increases in bio-available K concentrations were measured in plots in which 0-0-30 was applied in a subsurface band. The reason for this is unclear. Perhaps there was significant variation in measurable soil K in the direction of the application band, so that even with three replications, additional measurements may be necessary to identify areas with more bio-available K. Dr. Karlen is research soil scientist and Dr. Kovar is research soil scientist at the USDA-Agricultural Research Service in Ames, Iowa.
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