Sorry to say, but since many years ago it is well known that foliar analysis give different results every time a sample is taken if not done in July, preferably during its first half. That's why only during July is it possible to ascertain the nutritional status of the trees. The samples should consist in 100 leaves (four of each representative tree in the plot) taken from the middle part of the current shoots, the first leaves of the year arriving to full size.