2.2. Plant material, growth conditions and experimental setup
One-year-old L. decidua (European larch) seedlings were
purchased from a local nursery. On December 22, 2008 the soil
samples were placed in 7.5 l plastic pots, each one
filled with 6.7 kg
of the sampled soil (Fig. 1). During the
first 30 days the pots were
watered with distilled water three times per week to maintain a
constant weight (70% of
field capacity). SS was then applied to the
soil surface without incorporation into the soil. The rate of sludge
was equivalent to (30 t dry weight (DW) ha1: 30S) or twice (60 t
DW ha1: 60S) the maximum accumulated amount permitted
under French law (i.e., 30 t DW ha1 over a 10-year period). Pots
without sludge (0S) were used as the control. Each configuration
was replicated
five times. The plants were grown for 12 months in a
greenhouse with a 14 h photoperiod (200 mmol m2 s1), a
temperature regime of 25/14 C (day/night) and 60% relative
humidity.