The purpose of leaf analysis is:
- As an aid to evaluate the supplying capacity of the soil for nutritional elements;
- To evaluate the effect of treatments on the supplying capacity in the plant;
- To evaluate the relationship between the nutritional status of the plant and the plant reaction as an aid to estimation of fertilizer requirement;
- To diagnose deficiencies of nutritional elements; and
- To serve as a resource for evaluating new problems or to survey unknown areas.
Leaf and plant Analysis
The aim of leaf analysis (leaves, fruit etc.) is to relate the mineral content of the plant or part with its physical appearance, growth rate and yield or quality of the harvested product. This technique requires precise sampling procedures in respect of the selected plant part and the growth phase (time of sampling). The interpretation of results depends on the assumption that a significant biological relationship exists between the elemental content of the plant and its growth and/or production.
The way in which plants are sampled for analysis has a major effect on the results obtained. 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 to a large extent in respect of elemental composition and mixing of different organs in a compound sample is not recommended. The choice of the plant part to be sampled depends on two factors, viz. the best relationship between plant appearance or reaction with elemental composition and ease of identification and sampling. In the case of fruit trees, leaves located at the middles of shoots of the current season’s growth are sampled, while the youngest mature leaves of annual crops are sampled.
The best time to sample leaves of fruit trees is in the middle of the season and in South Africa samples are collected approximately on 31 January. If the sample is collected at a time which deviates greatly from the recommended time, corrections should be used. If it is necessary to collect samples earlier or later in order to determine causes of poor tree performance, trees in the problem spot as well as adjacent healthy trees should be sampled separately. Leaves should not be samples during the hottest part of the day since it can influence leaf composition. It is preferable to collect samples in the morning.
With annual crops the growth phase of the plant also affects the leaf composition. Consequently it is essential that the growth stage be indicated when samples are submitted to the laboratory.
With deciduous trees leaves are collected at shoulder height at the middle of the current season’s growth on both sides of the tree row. At least 50 leaves are collected per sample. In order to identify trends it is desirable that routine samples always be collected from the same trees, as already has been recommended for soil sampling. Trees should be clearly marked for this purpose. A poor spot in an orchard should be sampled separately.
For wine and table grapes the leaf opposite the bunch, or if removed, the leaf on a bearing shoot between nodes 3 and 5 are sampled. Thirty leaves without petioles are sufficient.
Samples are placed in a clean plastic or paper bag and should be kept cool until delivered to the laboratory. The samples must not be frozen under any circumstances.
World wide published data are available according to plant type and growth stage for interpretation of leaf analysis results.
For more information, please contact:
Bemlab: 021 853 1490