An SC900 recording penetrometer (Spectrum Technologies Inc)
was used to measure soil penetration resistance (kPa) at 2.5 cm
intervals to a maximum depth of 45 cm. Six soil profiles were taken
around each measured seedling, and averaged to obtain a mean
penetration resistance profile for that seedling. These values were
then averaged to obtain means for each treatment (30–120 profiles
per treatment). Soil strength measurements were combined into
four depth classes for analysis (0–10 cm, 10–20 cm, 20–30 cm
and 30–40 cm).