FIXED AMMONIUM AND POTASSIUM AS AFFECTED BY ADDED NITROGEN AND POTASSIUM IN 3 QUEBEC SOILS

Fixation of NH4+ 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 NH4+ 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.