FIXATION AND IMMOBILIZATION OF RECENTLY ADDED IN SELECTED ONTARIO AND QUEBEC SOILS
Low recovery of recently added [Formula: see text] fertilizer as [Formula: see text] 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, [Formula: see text] fixation was believed to be responsible for the low recovery. Between 18 and 23% of added [Formula: see text] was fixed after 15 d in the Bainsville and Dalhousie soils whereas only 1–3% of added [Formula: see text] 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 [Formula: see text] 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 soils after 15 d. Key words: Ammonium fixation, immobilization, vermiculites, 15N gamma radiation, potassium, native N, ammonium exchange