FIXATION AND IMMOBILIZATION OF RECENTLY ADDED IN SELECTED ONTARIO AND QUEBEC SOILS

Abstract

Low recovery of recently added NH4+ fertilizer as NH4 + NO3- was observed in a Bainsville (Orthic Humic Gleysol) and a Dalhousie (Gleyed Eutric Brunisol) soil, whereas a Brookston (Orthic Humic Gleysol) and a Conestogo (Gleyed Melanic Brunisol) soil had a high recovery. The former two soils had higher vermiculite contents than the latter two soils. Therefore, NH4+ fixation was believed to be responsible for the low recovery. Between 18 and 23% of added 15NH4+ was fixed after 15 d in the Bainsville and Dalhousie soils whereas only 1-3% of added 15NH4+ was fixed in the Brookston and Conestogo soils. Potassium pre-addition (with/without air drying) increased the apparent recovery in the Bainsville and Dalhousie soils but did not affect the actual recovery. Potassium pre-addition did not block subsequent 15NH4+ fixation, rather it resulted in a release of native 14N. Gamma irradiation was used to inhibit biological activity. Between 1 and 7% of added 15N was immobilized in these soil after 15 d.