108


different from that for the non-spiked set of cups, which had higher

concentrations of Ca and K in the passed solutions. The spike-soaked

set of cups showed no contamination and only minor adsorption of Ca

during the first passage. There were no differences between the passed

and remaining solution concentrations following the second increment

through the spike-soaked cups.

 Taken as a whole, the passed and the remaining solutions showed no

differences in solute concentration when compared to the original

control solution. Under no circumstances was the remaining solution-

solute concentration higher than for the control solution, thereby

ruling out the possibility of screening (restricted passage due to

steric or electrostatic effects). Even when differences existed between

passed and remaining solute concentrations, they were small and near the

detection limits of the analyzing instrument. Therefore, it may be

concluded that the cups had negligible adsorption, screening, or

contaminating effects when passing solutions of Ca, K, or NO,.

 The P-adsorption isotherm is presented in Fig. 6-2. The cups

 exhibited a strong affinity for P. Such behavior precludes using the

 cups for extraction and consequent determination of soil-solution P

 concentrations. Similar behavior has been previously reported (Bottcher

 et al., 1984).

 Nutrient Movement

 The soil solutions were stored for I1 to 30 wk before chemical

 analysis due to problems with instruments. Although the samples were

 acidified (pH < 2) and kept refrigerated, the time period exceeded

 generally-accepted standards for quantitative analysis of NO3 and NH4,