ABSTRACT
Nitrogen (N) is the major nutrient determining tree growth, and this has been demonstrated
abundantly in the Boreal Shield with fertilization trials or net N mineralization studies (e.g.,
Attiwil and Adams 1993; Reich et al. 1997). However, Ingestad (1979a,b) also showed that
any other nutrient (but particularly phosphorus (P) and potassium (K)) could be limiting if
supplied at a rate lower than tree demand, even if N was in excess. For example,
fertilization trials with N alone or in combination with P, K, or both stimulated the growth
of black spruce (Picea mariana (Mill.) BSP) (e.g., Wells 1994; Paquin et al. 1998) and jack pine (Pinus banksiana Lamb.) (e.g., Morrison and Foster 1995; Weetman et al. 1995). A much lower number of studies have showed the benefits of increased calcium (Ca) and
magnesium (Mg) availability on tree nutrition and yields in Canadian forests (Hamilton
and Krause 1985; Bernier and Brazeau 1988; Thiffault et al. 2006). A review by Binkley and
Ho¨gberg (1997) suggested that fertilization trials with Ca and Mg have only occasionally
favored the growth of northern tree species. The benefits of Ca and Mg fertilization may
actually be related to an indirect effect of liming on N availability (Nohrstedt 2001;
Sikstro¨m 2002). The lack of scientific evidence about the role of soil nutrients (other
than N) on improved tree nutrition and growth may be due to the fact that permanent site
variables such as climate, drainage, and soil physical properties have a stronger influence
on trees (Post and Curtis 1970).
