Fjölrit RALA - 15.06.2004, Page 124

Phosphate sorption of European volcanic soils
Gy. Fúleky
Szent István University Gödöllo Hungary
Hypothesis: The P adsorption isoterms give more information about the soils developed on
volcanic material than the phosphate retention percent.
Method:
1 g soil was equilibrated with 0; 50; 100; 500; 1000; 3000; 5000 and 10 000 mgkg"1
respectively, for 24 hours.
Data analysis: P isotherms
t . . „ . Pads k-c
Langmun1 equation Pads -------------------
1 + k-c
The P ads max, the maximum amount of phosphate could be sorbed, can be used as a soil
characteristic in further statistical calculations.
Soils:19 European volcanic soil profiles and other Hungarian, Rumanian and Slovakian
volcanic soils (n = 126).
Fig.l. demonstrates the shape of soil phosphate adsorption isoterms of low and high
phosphate adsorption capacity. Some soils of high phosphate fixing capacity can adsorb much
more phosphate than 5000 mgkg'1, the applied concentration at Pret% determination. At the
same time k value, which is in correlation with the bonding energy, could explain the
uncovered relationships. That is the soils of No5; 6; 10 and 15 which bond the phosphate
more strongly.
Pads m„ mgkg'1
Figure 1 P adsorption isotherms of some European volcanic soils
Table 1. Linear relationship between some soil characteristics and P adsorption maxima
Soii characteristic R2 Soil characteristic R2 Soil characteristic R2
Alp/Alo No Bases 0,1543 Fe0 % 0,651
Feo/Fed No CEC 0,3998 Ald % 0,711
Base saturation % No P retention % 0,449 Al0 % 0,724
PHh20 No Fed% 0,479 Al0% + >/2 Fe0 % 0,724
Exchangeable Ca No Allophane (Parfitt) 0,633 Al0 % + Alp % 0,732
Total organic C% 0,139
100