Concentrations of nutrients in soil solution may by important indicators of
nutrient availability for forest plantations, but we were unaware of the e
xtent to which these concentrations varied temporally and were affected by
fertilizer treatments at various sites, The effect of fertilizing eucalypt
plantations on the concentrations of NH4, NO3, and inorganic phosphate (Pi)
, and on electrical conductivity (EC) and pH in paste extracts was assessed
at three sites in Tasmania, Australia, Nitrogen and P fertilizers were bro
adcast at elemental rates in the range 0 to 600 kg ha(-1) as (NH4)(2)SO4 an
d triple super-phosphate within 2 mo of planting, and again at 26 mo at two
of the sites. Nutrient concentrations in undiluted soil solution were infe
rred by adjusting for the effects of dilution and buffering. Both fertiliza
tion events decreased pH by up to one-half a unit, and increased conductivi
ty and the concentrations of NF4 and P-i by up to 10-fold in the 0- to 60 c
m depth at all sites. Even at the highest rate of application, values of al
l parameters generally returned to unfertilized values before the second ap
plication of fertilizer, Rates of decrease in concentrations of NH4 and P-i
after fertilization were unaffected by the age of the crop. When broadcast
, applications of fertilizers may be needed at 2- to 4-yr intervals to main
tain high nutrient availability. A single application of (NH4)(2)SO4 to the
se soils at a typical rate of 200 kg N ha(-1) will have minimal effect on p
H, but multiple applications could decrease pH and adversely affect Ca, K,
and Mg availability.