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three split-applications each added 6.5% of the total Ca and P, but 25%

of the total K (as well as NO3 and NH4).

 It is also important to note that the placement of the ceramic

extraction cups and the suction used to withdraw the soil solution

influence the size and location of the extraction zone (van der Ploeg

and Beese, 1977). Due to the clayey nature of the soil's fine fraction

several procedural considerations are required to prevent migration of

clay into the cups and subsequent plugging of the cups' porous network.

The holes drilled into the columns were first lined with a thin layer of

fine sand before insertion of the extraction cup. This requires the

soil solution to first cross a thin sand bridge before reaching the

extraction cup. The suction used to extract the soil solution was

chosen so that sufficient soil water was available for extraction and so

that migration and lodging of clay in the cups was minimal (Hansen and

Harris, 1975; Talsma et al., 1979).

 The size of the extraction cups (28.6 mm long by 6.35 mm o.d.)

 preclude their installation into exclusively small or large pores.

 Since the previous chapter indicated the presence of both immobile-water

 regions and preferential flow in macropores at near saturated

 conditions, the soil solution was probably extracted predominantly from

 the larger pores.