106

 The adsorption of P to the ceramic cups was investigated using the

method of Nair et al. (1984). Duplicate extraction cups were placed,

one per 50-mL screw-top centrifuge tube, and allowed to equilibrate for

24 h in 25 mL of 0.01 M CaC12 solution with one of several

concentrations of KH2PO4. Solution P concentrations were determined by

the ascorbic acid/ammonium molybdate method (Olsen and Sommers, 1982).

 Results and Discussion


 Extraction Cups Test

 The concentrations of solutes in the passed and remaining

 solutions from each extraction-cup treatment are presented in Table 6-1.

 Analysis of variance and orthogonal contrasts were calculated to

 determine the effects of the treatments on the various solutions (Table

 6-2). Concentrations of both Ca and K in the passed solutions were

 higher than in the remaining solutions, after the first passage of the

 test solution. This indicated that some contaminating Ca and K remained

 in the cups after the initial washing process. However, the

 concentrations of Ca and K in the passed and remaining solutions for the

 next two increments were not different. The concentrations of NO3 in

 the passed and remaining solutions were not different for any of the

 three increments.

 The dilute spike solution was used to satisfy minor completing

 sites and, thereby, reduce the possible adsorption of solutes during

 later experimental use. After pre-soaking the cups in the spike

 solution, the concentration of Ca in the passed solution was

 significantly less than that in the remaining solution. This result was