114

 The concentration of soil-solution Ca, K, and Mg with depth during

the water-application periods for the five column treatments are shown

in Figs. 6-4, 6-5, and 6-6, respectively. The intercepts (I) and

coefficients (xi) of the response surface equations including quadratic

and crossproduct effects:

Solute (ug/mL) = I + x,(Depth) + x2(Day) + X3(Depth*Day) +

 x4(Depth2) + xs(Day2) [6-1]

for each nutrient and treatment are presented in Table 6-5. The

concentrations of Ca, K, and Mg in the soil solution for all treatment

exhibited an initial peak in the soil surface (0 to 10 cm) and a near

absence of the nutrient in the subsoil (50 to 70 cm). As the season

progressed, the surface concentrations decreased greatly and the subsoil

concentrations increased slightly, as the solutes moved convectively

down with flowing water and moved diffusively into immobile soil water

regions.

 The magnitudes of the initial peaks were dependent on the

fertilizer treatment. The highest fertilizer application rate

demonstrated the highest soil-solution concentration, while the non-

fertilized control typically had the lowest initial solution

concentration. For Ca and K, this may be explained by their presence in

the fertilizer; however, for Mg the increased soil solution

concentrations with increased fertilizer application, was due to the

competitive selectivity the fertilizer ions have for the soil surface

and the ability of the newly added ions to displace Mg from the surface

phase to the solution phase.