Fixed ammonium and potassium release from two soils

Abstract Release of native and added K+ and NH+ 4 from two soils was monitored during a 166 day incubation/leaching experiment. One soil (Brookston) represented a major soil series In Ontario whereas the other (Harriston) was suspected having a relatively large fixation capacity. Treatments were imposed involving addition of 50 μM g‐1 soil of K+(KCl) or NH+ 4 (NH4Cl) only or one added after the other on successive days. The addition of either K+ or NH+ 4 on day 2 tended to inhibit the release of the other added on day I. Also the addition of either K+ or NH+ 4 on day 1 tended to inhibit the sorption or fixation of the other on day 2. The release rate of K+ during the 10 to 166 day period was almost constant and not affected by the addition of NH+ 4. Alternatively, the addition of K+ on day 2 slowed the release rate of NH+ 4 measured by NO− 3 appearance from day 10 to 40 but had no effect thereafter. At the end of the experiment considerably more K+ than NH+ 4 was retained suggesting that K+ was more firmly fixed. However, the continuing nitrification of NH+ 4 must be contrasted with periodic removal of K+ by leaching with 0.01 M CaCl2 solution since the equilibrium between exchangeable and fixed ions was affected. There were no notable differences between the two soils inspite of a considerable difference in clay content.