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

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.