『Abstract
Equilibrium phosphorus concentration (EPC) is the aqueous phosphorus
(P) concentration at which no net adsorption or desorption occurs
when a soil is in contact with water; and are typically determined
experimentally by plotting the measured amount of sorption versus
initial concentration of P. In this study we evaluated the effect
experimental parameters such as equilibration time, soil:solution
ratio (SSR), and solution electrolyte may have on EPC values for
two distinctly different soil types, (i) organic muck soil, and
(ii) loamy mineral soil. Results indicate that there is a significant
difference in emerging EPC values with changing equilibrium time,
SSR, and electrolyte. For the muck soil, we observed up to 97%
decrease in EPC while increasing equilibration time from 1 to
8 h using 1:10 SSR. For the same soil the most profound effect
of SSR was observed for 1 h equilibration where EPC value decreased
from 0.19 mg L-1 using 1:2 SSR to 0.03 mg L-1
using 1:20 SSR, corresponding to an 84% change. The EPC of the
loamy soil decreased by 94% while increasing equilibration time
from 24 to 72 h using 1:20 SSR, whereas the same soil change in
SSR was highly variable. Overall there was a 38% increase in EPC
values using 0.01 M CaCl2 compared to KCl
as the solution electrolyte in the experiment. These results indicate
that experimental conditions can significantly affect EPC values
(besides other factors) and therefore need to be standardized
especially when used as a tool to assess P loading in natural
systems.
Keywords: Equilibrium; Phosphorus; Soil; Adsorption; Desorption;
Langmuir』
1. Introduction
2. Materials and methods
3. Results and discussion
3.1. Effect of soil:solution ratio on EPC
3.2. Effect of equilibration time on EPC
3.3. Effect of cation electrolyte on EPC
3.4. Role of pH and soil type in evaluating P mobilization
3.4.1. pH
3.4.2. Soil composition
4. Conclusions
Acknowledgments
References