TRD: Institute for Plant Production: Laboratory Services: SOIL, WATER AND PLANT TISSUE LAB
Plant leaf sampling
General
Leaf analysis is a useful tool that can easily be used by growers to improve the management of nutrients. Leaf sampling for nutrient levels is a standard practice in the production of perennial crops.
Leaf sampling will aid in determining fertiliser needs and problem diagnosis. Regular leaf and soil sampling and the visual monitoring of plants will help determine the overall health of crops. A healthy stand has a high density of stems and bright, green leaves. Discoloured leaves may indicate a nutrient deficiency.
The appearance of apparent mineral deficiency symptoms may be the result of an actual deficiency, or could be caused by several other conditions or combinations of conditions including:
- Insufficient or poor soil moisture distribution, and/or topsoil erosion.
- Poor drainage and subsequent restriction of the root system.
- Insects, disease, fertiliser burn, weeds, or compaction of the soil - all of which weaken the root system.
- Periods of cool weather during the growing season.
- Injury from herbicides.
You should be sure that none of the above conditions exist before making additional fertiliser applications.
Sampling procedure
Introduction
Leaf analysis enables us to directly measure the nutritional status of the trees or vines. The results can then be compared with known standards to determine whether the tissues contain excessively high or low concentrations of critical macro and micro nutrient elements. The nutrient supply can then be adjusted to bring the levels of the mineral nutrients in the tissues back to within acceptable limits.
How should leaf samples be taken?
Leaf sampling should be carried out annually, and must be done correctly if reliable results are to be obtained. Since the levels of most elements in the leaves change during the course of the season, it is particularly important that leaf sampling should be carried out at the correct time.
Fruit orchards
- Pick the sample in the last week of January, or the first week in February, from non-bearing shoots produced in the current season.
- Sample mature leaves from the middle of the shoot, at shoulder height.
- Choose sufficient, evenly spaced trees to be representative of the whole orchard.
- Sample the full perimeter of the tree (not just one side or another).
- The total sample should consist of a minimum of 40 leaves.
- Different cultivars should be sampled separately.
Vineyards
- Sample at fruit set (usually the last week in November, but the timing may differ according to cultivar/region).
- Sample leaves from positions opposite to the developing bunches.
- It is usually sufficient to analyse the petiole only. The leaf blade must be separated from the petiole immediately after sampling in order to minimise translocation of nutrients.
- The ideal is to analyse both the blades and the petioles, but this will double the analytical cost.
- The total sample should consist of at least 40 petioles and/or leaves.
Each leaf should be picked by hand. Place the leaves in a clean, perforated plastic bag. If the samples must be stored, or transported over a large distance, they must be kept in cold storage and transported in an insulated container to keep them fresh. Circumstances under which the leaves are likely to become mouldy should be avoided. If unavoidable delays are likely to occur in getting the samples to the laboratory, it is permissible to dry the leaves thoroughly in the sun before transportation.
The following information must accompany the samples:- Owner’s name and surname.
- Farm name and postal address.
- Orchard/vineyard name or block number.
- Fruit kind and cultivar.
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