Soil biological activity analysis and ecotoxicological testing

2.2. Tree growth and nutrition monitoring
Tree height and diameter at breast height were measured annually for all plots from tree age 6 in 1997 to 19 years in 2010. Stocking, mean top height, basal area and stem volume were estimated for each subplot as described previously (Wang et al., 2006). To assess tree nutritional status, samples of current-year foliage were collected in autumn (March) annually from 1998 from AZD8931 top third of the crowns of randomly selected trees in each plot. Foliar samples were bulked across stocking density treatments within each main-plot before being analysed.
2.3. Soil chemical and physical property assessment
Soil chemical properties were assessed at three depths using samples taken from the forest-floor litter layer, topsoil (0–25 cm) and subsoil (25–50 cm) in May 2010. Samples were taken from all subplots within each biosolids treatment main-plot and bulked, resulting in four replicate samples per biosolids treatment. The foliage and litter samples were oven-dried (70 °C) and ground for chemical analysis. Soil samples were air-dried and ground to pass through a mutation rate 2-mm-mesh sieve for chemical analysis.