25 Feb Sampling Leaves for Chemical Analyses
The aim of plant analysis (leaves, fruit etc.) is to relate the mineral content of the plant (or part thereof) with its physical appearance, growth rate and yield or quality of the harvested product, and also with the nutrient content of the soil. Precise sampling procedures with respect to the selected plant part and the growth phase (time of sampling) are required. The interpretation of results depends on the assumption that a significant biological relationship exists between the elemental content of the soil, the plant and its growth rate or production.
The purpose of plant analysis therefore is:
An aid to evaluate the supplying capacity of the soil for nutrients;
To evaluate the response of the plant to fertiliser applications;
Plants consist of complex structures of which the elemental composition is not homogenous. It is known that leaves, stems, shoots and fruit, as well as the position of the organ on the plant, differ in elemental composition. Mixing of different organs in a compound sample is therefore not recommended. The choice of the plant part to be sampled needs to be properly selected.
Refer to Table 1 to ensure that the correct plant part and number of leaves are sampled, during the most appropriate time.
Trees/plants at the edge of the block and at the end of rows should not be sampled – they may be coated with soil/dust particles and/or differ in their nutrient status and irrigation regime from the rest of the block. Do not sample diseased, insect damaged, or dead leaves. Leaves should not be sampled during the hottest part of the day since it can influence leaf composition.
Trees/plants in a problem spot, as well as adjacent healthy ones should be sampled separately. To identify seasonal trends in perennial crops, it is desirable that routine samples are always collected from the same trees – trees should be clearly marked for this purpose.
Collect samples in the morning, place the leaves in a clean plastic or paper bag and keep it cool until delivered to the laboratory. Do not freeze it under any circumstances.