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The Plant Laboratory at Cedara: Elemental analysis of plant tissues
Analysis of plant tissues
Plant tissue analysis has numerous practical applications, but the primary use of the plant analysis technique is to diagnose or confirm nutrient deficiencies, toxicities, or imbalances and to monitor nutrient supply and uptake.
Interpretation of plant analyses
The nutrient element concentration within the plant is related to the supply and availability of nutrients in the soil, so plant analysis can be used to detect nutrient disorders (shortages or toxic levels of particular elements). Plant analysis complements the use of soil testing because reliable soil tests are not available for all essential plant nutrients and soil tests are primarily designed to predict the possible occurrence of deficiencies or excesses in a crop that has not yet been planted. Plant analysis indicates directly what the nutritional status of the plant is at the time of sampling.
However, there are difficulties associated with the use of plant analyses:
- Plant analysis cannot identify the cause of nutrient uptake problems or nutritional disorders.
- It does not indicate the quantity of fertilizer that must be applied to the soil to correct a nutritional disorder.
- Analysis of plant tissue usually reveals only one nutrient deficiency at a time.
- Other factors affecting plant growth, such as drought, can affect the interpretation of plant analyses.
- Most nutrient deficiencies, unless extremely severe, tend to develop during the latter stages of growth. In the case of annual crops, therefore, it is usually too late to do anything about the problem in the current growing season. This is less of a problem in perennial plants such as fruit trees and permanent pastures.
Although plant analysis can identify nutrient uptake problems or nutritional disorders, the technique has limitations and it is thus not a substitute for routine soil analysis. Rather, soil fertility and plant nutritional problems are best identified and solved using plant analysis in conjunction with soil testing.
Sampling for plant analysis:
For diagnostic purposes, plant samples are usually collected from an area of poor growth and from an adjacent area of good growth in the same field. It is important that samples be collected as soon as poor growth is noticed.
The plant part chosen for analysis is usually the leaf since it is metabolically active and, therefore, its composition provides useful information on changes in the nutritional status of the plant. The plant analysis technique is not, however, restricted to using leaves and the choice of the plant part to analyse may, on occasion, involve the seed, fruit, plant sap or some other organ.
Reference nutrient concentrations are available for many crops. These can be compared to sample results to assess nutrient status with respect to deficiency, adequacy or toxicity. However, these reference concentrations refer to specific plant parts, position of the part on the plant and stage of growth. It is important, therefore, that samples submitted to the laboratory for analysis correspond with established sampling procedures. Failure to do so will lead to incorrect interpretation and recommendations.
Before taking a plant tissue sample, find out what norms are available for comparison purposes, and sample the appropriate plant part at the correct time (you need to be able to compare your results with established norms for the same part of the plant of the same age).
More information is available from Cedara (033 - 3559 455). There are also a number of useful text books which can be consulted:-
- an interpretive manual: D.J. Reuter and J.B. Robinson.
- Plant analysis
- Soil testing an plant analysis
: L.M. Walsh and J.D. Beaton
- Plant Analysis as a guide to the nutrient requirements of temperate and tropical crops
: P. Martin-Prevel, J. Gagnard and P. Gautier
Plant Laboratory
The Plant Laboratory is responsible for the elemental analysis of plant tissues (usually leaves), and other organic materials such as composts and manures. This service is used extensively by both farmers and researchers, thereby promoting the more efficient use of plant nutrients.
Analysis of plant material allows assessment of the nutritional status of crops (if samples are taken correctly) and can give an indication of the quantities of different nutrients used by a crop. Analyses of manures and composts give an indication of their ability to supply nutrients to crops.
Analyses undertaken are:
elemental analysis (minerals); total nitrogen, sulphur, phosphorus, potassium, calcium, magnesium, sodium, zinc, copper, manganese and boron
ash
pH of growing media
moisture
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Soil Fertility and Analytical Services
KwaZulu-Natal Department of Agriculture
Private Bag X9059
Pietermaritzburg
3200Contacts:
Suzie Riekert, Ruby Punwasi or Vino Naidoo
Telephone: (033) 3559455/6
Facsimile: (033) 3559454
