Effect of wetting and drying of soils on phosphate adsorption and resin extraction of soil phosphate

Sixteen topsoils from Denmark and the UK were subjected to two wetting and drying treatments: (i) moist incubation (wet), (ii) eleven wetting and drying cycles (W/D). The W/D treatment resulted in larger P adsorption and resin extraction of soil P than the wet treatment. The differences in P adsorption at the final concentration of 800 μM P were mainly above 20 per cent, whereas the differences in amount of resin-extracted P were mainly less than 20 per cent. The effects were positively correlated with the cation exchange capacity of inorganic components. Furthermore, the increase in rapidly released P was positively correlated with pH. It is suggested that wetting and drying effects on P adsorption and desorption are associated with changes in soil structure caused by rewetting of dry samples.