Picking the correct leaf to conduct a leaf analysis is important. Testing incorrect leaves can result in incorrect leaf readings that will not provide a proper indication of the orchards nutritional status.
Leaf analysis interpretation charts were developed in USA in the early 1960's. The interpretation chart was developed sampling thousands of orchards of know health and cropping performance. Results from the higher productive orchards were used to develop the optimum leaf nutrient standards currently used in leaf analysis interpretation charts.
The leaves picked to develop this standard were 4 to 7 month old leaves from non fruiting terminals, the 3rd and 4th leaves of these shoots are sampled. These leaves were picked in the Australian equivalent of mid February to mid March. Leaf analysis guides from USA continue to advise leaf samples to be taken in this period. Four to seven month old leaves would have emerged from spring flush in the August to October period.
It is important to note that leaf analysis is not the only source of information to help determine whether your trees are recieving sufficent nutrition. Others include field observation of tree health and vigour, fruit quality and yield, soil chemistry and type, and irrigation method.