Timing of sampling
Only fully expanded undamaged leaves from the outside of the crown, exposed to full light, should be sampled, from late July to the end of August, when concentrations of the nutrients are steady.
Selection of samples
Leaves soiled by birds must be avoided but dust has little effect on the concentrations of major nutrients, so dusty leaves are usually acceptable.
Nutrient concentrations vary less with aspect and height than between healthy and deficient trees. In contrast, nutrient concentrations in basal suckers and pollard shoots may be high and misleading. Leaves should therefore be collected from a convenient position on the outside of the true crown.
Enough leaves to cover an A4 sheet of paper, but excluding the petioles, should be collected from large or well-established trees. Recently planted trees rarely have enough foliage for this size of sample, so a composite sample from 5-10 trees of each species should be taken.
Age of foliage
There is little point in sampling trees until at least two growing seasons after planting since before then they will not be in equilibrium with the site and nutrient concentrations may still reflect the nursery nutrient regimes.
If there is sufficient variation in vigour and current shoot growth to distinguish good and poor trees, separate samples should be made up from each category. If many trees are involved, replicate samples from each category will aid interpretation. Markedly different vegetation types should be sampled separately.
Dispatching samples for analysis
Leaf samples, fully labelled, should be packed in polythene bags and despatched as soon as possible to Environmental Research Laboratory, Alice Holt. If delay in despatch is likely, the packed samples should be stored in a cool place.