Citrus leaf sampling for nutrient analysis

Introduction

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 known 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.

Pictorial Guide

A pictorial guide on selecting the correct leaves to sample is given in figures 1 to 5 below.

Figure 1 Wrong leaf - This is a young expanding flush. Notice the light colour and glossy appearance of the leaves.

Figure 2 Wrong leaf - This is a summer flush.  Summer flushes emerge during warm to hot conditions where leaf expansion is rapid.  This results in a large oval/round shaped leaf.

Figure 3 Wrong leaf - This is a late spring/early summer flush.  These leaves are confusing because they are in the transitionary period between a spring and a summer flush.  These leaves are often confused for a spring flush because they seem to be the correct length, and if the leaf is slightly curled, it misleadingly appears to be narrow.

Figure 4 Correct leaf - This is typical of a spring flush.  Notice the medium sized leaf and the narrow and pointed appearance.  It is the narrow and pointed appearance that is the major determining factor in identifying spring flush shoots.  Leaves that emerge in spring grow under mild/cool conditions and thus the leaves do not grow as broad and as large as the summer flush leaves.

Figure 5 Correct leaf - The three leaves visible on the top left hand corner of the picture is spring flush.  It has been termed as ‘dogs’ ear’ in appearance.  The flush (three leaves) on the bottom right hand side of the picture seem to be more oval in shape and thus should be avoided.