Fixed ammonium and potassium as affected by added nitrogen and potassium in three Quebec soils

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Abstract
Fixation of NIL4 + and K+ by soil clays affects N and K availability to plants, and fixation may be a result of N source or method of application. An incubation study with urea, NH4Cl and KCl was conducted to evaluate NH4 + and K+ fixation in three southern Quebec soils. Soils contained significant amounts of native‐fixed NIL4 + and K+ and showed relatively high NH4 + and K+ fixing capacities. NH4 + fixation was increased with increased N rates and was reduced with increased K rates with urea. With NH4Cl, an increase of fixed NH4 + was noted with increased K rates. By contrast, K+ fixation was enhanced consistently with increased K rates and was decreased with increased N rates. The soils fixed a lower proportion of added N but a higher proportion of added K when urea was the N source in comparison with NH4Cl. A delayed NH4 + appearance due to urea hydrolysis enhanced K+ fixation.